refactor(git): rename stage_hunk to toggle_stage

init.lua

@@ -30,7 +30,6 @@ require("pack").setup({
     "https://github.com/owallb/mason-auto-install.nvim",
     "https://github.com/mfussenegger/nvim-dap",
     "https://github.com/numToStr/Comment.nvim",
-    "https://github.com/lewis6991/gitsigns.nvim",
     "https://github.com/MagicDuck/grug-far.nvim",
     "https://github.com/nvim-tree/nvim-tree.lua",
     "https://github.com/stevearc/oil.nvim",

lua/core/autocommands.lua

@@ -66,6 +66,18 @@ vim.api.nvim_create_autocmd({ "BufReadPost" }, {
     command = 'silent! normal! g`"zv',
 })
 
+vim.api.nvim_create_autocmd("BufWinEnter", {
+    desc = "Reset foldlevel to 0 when entering a diff window."
+        .. " Vim's partial diff-state restoration on buffer re-entry"
+        .. " (e.g. via <C-o>) doesn't re-apply foldlevel=0, so"
+        .. " foldlevelstart leaks through and folds appear open.",
+    callback = function()
+        if vim.wo.diff then
+            vim.wo.foldlevel = 0
+        end
+    end,
+})
+
 vim.api.nvim_create_autocmd("FileType", {
     pattern = { "c" },
     callback = function()

lua/core/keymap.lua

@@ -226,11 +226,18 @@ vim.keymap.set("n", "<leader>fD", vim.diagnostic.setqflist)
 vim.keymap.set("n", "grt", vim.lsp.buf.type_definition)
 vim.keymap.set("n", "gd", vim.lsp.buf.definition)
 
-vim.keymap.set("n", "<leader>gd", "<Plug>(git-diff-vertical)")
+vim.keymap.set("n", "<leader>gd", "<Plug>(git-diffsplit-vertical)")
-vim.keymap.set("n", "<leader>gD", "<Plug>(git-diff-vertical-head)")
+vim.keymap.set("n", "<leader>gD", "<Plug>(git-diffsplit-vertical-head)")
-vim.keymap.set("n", "<leader>gh", "<Plug>(git-diff-horizontal)")
+vim.keymap.set("n", "<leader>gh", "<Plug>(git-diffsplit-horizontal)")
-vim.keymap.set("n", "<leader>gH", "<Plug>(git-diff-horizontal-head)")
+vim.keymap.set("n", "<leader>gH", "<Plug>(git-diffsplit-horizontal-head)")
 vim.keymap.set("n", "<leader>gg", "<Plug>(git-status-toggle)")
 vim.keymap.set("n", "<leader>gc", "<Plug>(git-commit)")
 vim.keymap.set("n", "<leader>ga", "<Plug>(git-commit-amend)")
 vim.keymap.set("n", "<leader>gl", "<Plug>(git-log)")
+vim.keymap.set("n", "<leader>gv", "<Plug>(git-hunk-select)")
+vim.keymap.set("n", "<leader>gs", "<Plug>(git-hunk-stage-toggle)")
+vim.keymap.set("n", "<leader>gr", "<Plug>(git-hunk-reset)")
+vim.keymap.set("n", "<C-w>g", "<Plug>(git-hunk-preview)")
+vim.keymap.set("n", "<leader>go", "<Plug>(git-overlay-toggle)")
+vim.keymap.set({ "n", "x" }, "]g", "<Plug>(git-hunk-next)")
+vim.keymap.set({ "n", "x" }, "[g", "<Plug>(git-hunk-prev)")

lua/git/core/repo.lua

@@ -123,6 +123,16 @@ local function affects_resolve(relpath)
         or relpath == "FETCH_HEAD"
 end
 
+---@private
+---@param prefix string
+function Repo:_clear_cache_prefix(prefix)
+    for key in pairs(self._cache) do
+        if vim.startswith(key, prefix) then
+            self._cache[key] = nil
+        end
+    end
+end
+
 ---@private
 ---@param relpath string
 function Repo:_invalidate(relpath)
@@ -132,11 +142,11 @@ function Repo:_invalidate(relpath)
         end
     end
     if affects_resolve(relpath) then
-        for key in pairs(self._cache) do
+        self:_clear_cache_prefix("resolve:")
-            if vim.startswith(key, "resolve:") then
+        self:_clear_cache_prefix("head_blob:")
-                self._cache[key] = nil
-            end
     end
+    if relpath == "index" then
+        self:_clear_cache_prefix("index:")
     end
 end
 
@@ -587,6 +597,24 @@ function Repo:rev_parse(rev, short)
     return trimmed ~= "" and trimmed or nil
 end
 
+---@param rel string  worktree-relative path
+---@return string?
+function Repo:index_sha(rel)
+    local sha = self:get_cached("index:" .. rel, function(self)
+        return self:rev_parse(":" .. rel, false) or false
+    end)
+    return sha or nil
+end
+
+---@param rel string  worktree-relative path
+---@return string?
+function Repo:head_sha(rel)
+    local sha = self:get_cached("head_blob:" .. rel, function(self)
+        return self:rev_parse("HEAD:" .. rel, false) or false
+    end)
+    return sha or nil
+end
+
 ---@alias ow.Git.Repo.ResolveStatus "ok"|"ambiguous"|"missing"
 
 ---@param abbrev string
@@ -819,7 +847,7 @@ end
 
 ---@param buf integer
 ---@return boolean
-local function is_worktree_buf(buf)
+function M.is_worktree_buf(buf)
     if not vim.api.nvim_buf_is_valid(buf) or vim.bo[buf].buftype ~= "" then
         return false
     end
@@ -830,7 +858,7 @@ end
 ---@param buf? integer
 function M.track(buf)
     buf = expand_buf(buf)
-    if not is_worktree_buf(buf) then
+    if not M.is_worktree_buf(buf) then
         return
     end
     local r = M.resolve(buf)

lua/git/core/util.lua

@@ -194,6 +194,65 @@ function M.debounce(fn, delay)
         }
 end
 
+---@class ow.Git.Util.KeyedDebounceHandle<K>
+---@field cancel fun(key: K)
+---@field flush fun(key: K)
+---@field pending fun(key: K): boolean
+---@field close fun()
+
+---@generic K, F: fun(key: K, ...)
+---@param fn F
+---@param delay integer
+---@return F, ow.Git.Util.KeyedDebounceHandle<K>
+function M.keyed_debounce(fn, delay)
+    ---@type table<any, { call: fun(...), handle: ow.Git.Util.DebounceHandle }>
+    local slots = {}
+
+    local function call(key, ...)
+        local t = type(key)
+        assert(
+            t == "string" or t == "number" or t == "boolean",
+            "key must be a primitive (string, number, boolean)"
+        )
+        local slot = slots[key]
+        if not slot then
+            local c, h = M.debounce(function(...)
+                fn(key, ...)
+            end, delay)
+            slot = { call = c, handle = h }
+            slots[key] = slot
+        end
+        slot.call(...)
+    end
+
+    return call,
+        {
+            cancel = function(key)
+                local slot = slots[key]
+                if slot then
+                    slot.handle.close()
+                    slots[key] = nil
+                end
+            end,
+            flush = function(key)
+                local slot = slots[key]
+                if slot then
+                    slot.handle.flush()
+                end
+            end,
+            pending = function(key)
+                local slot = slots[key]
+                return slot ~= nil and slot.handle.pending()
+            end,
+            close = function()
+                for _, slot in pairs(slots) do
+                    slot.handle.close()
+                end
+                slots = {}
+            end,
+        }
+end
+
 ---@class ow.Git.Util.ExecOpts
 ---@field cwd string?
 ---@field stdin string?

lua/git/diffsplit.lua

@@ -5,7 +5,7 @@ local util = require("git.core.util")
 
 local M = {}
 
----@class ow.Git.Diff.SplitOpts
+---@class ow.Git.Diffsplit.OpenOpts
 ---@field target string?
 ---@field mods vim.api.keyset.cmd.mods?
 
@@ -107,8 +107,8 @@ local function default_split(cur_buf, target)
     return nil
 end
 
----@param opts? ow.Git.Diff.SplitOpts
+---@param opts? ow.Git.Diffsplit.OpenOpts
-function M.split(opts)
+function M.open(opts)
     opts = opts or {}
     local cur_buf = vim.api.nvim_get_current_buf()
     local target, err

lua/git/hunks.lua

@@ -0,0 +1,970 @@
+local repo = require("git.core.repo")
+local util = require("git.core.util")
+
+local M = {}
+
+local NS_SIGNS = vim.api.nvim_create_namespace("ow.git.hunks")
+local NS_OVERLAY = vim.api.nvim_create_namespace("ow.git.hunks.overlay")
+
+---@alias ow.Git.Hunks.HunkType "add"|"change"|"delete"
+
+---@class ow.Git.Hunks.Hunk
+---@field old_start integer  1-indexed first old line
+---@field old_count integer
+---@field new_start integer  1-indexed first new line
+---@field new_count integer
+---@field type ow.Git.Hunks.HunkType
+---@field old_lines string[]
+---@field new_lines string[]
+
+---@class ow.Git.Hunks.BufState
+---@field repo ow.Git.Repo
+---@field rel string
+---@field index string[]?
+---@field index_sha string?
+---@field head string[]?
+---@field head_sha string?
+---@field index_hl { src: string[], lines: table[][]? }?
+---@field hunks ow.Git.Hunks.Hunk[]
+---@field staged ow.Git.Hunks.Hunk[]
+---@field overlay boolean
+---@field autocmds integer[]
+
+---@type table<integer, ow.Git.Hunks.BufState>
+local states = {}
+
+---@param buf integer
+---@return ow.Git.Hunks.BufState?
+function M.state(buf)
+    return states[buf]
+end
+
+---@param buf integer?
+---@return integer
+local function resolve_buf(buf)
+    return buf and buf ~= 0 and buf or vim.api.nvim_get_current_buf()
+end
+
+---Mirror the hunk-affecting parts of the user's 'diffopt' so the gutter
+---lines up with what `:diffsplit` shows.
+---@return table
+local function diff_opts()
+    local opts = { result_type = "indices", algorithm = "myers" }
+    for _, item in ipairs(vim.split(vim.o.diffopt, ",", { plain = true })) do
+        if item == "indent-heuristic" then
+            opts.indent_heuristic = true
+        else
+            local algorithm = item:match("^algorithm:(.+)$")
+            if algorithm then
+                opts.algorithm = algorithm
+            end
+            local linematch = item:match("^linematch:(%d+)$")
+            if linematch then
+                opts.linematch = tonumber(linematch)
+            end
+        end
+    end
+    return opts
+end
+
+---@param old_lines string[]
+---@param new_lines string[]
+---@return ow.Git.Hunks.Hunk[]
+local function compute_hunks(old_lines, new_lines)
+    local raw = vim.text.diff(
+        table.concat(old_lines, "\n"),
+        table.concat(new_lines, "\n"),
+        diff_opts()
+    )
+    ---@type ow.Git.Hunks.Hunk[]
+    local hunks = {}
+    if type(raw) ~= "table" then
+        return hunks
+    end
+    for _, h in ipairs(raw) do
+        local os_ = h[1] --[[@as integer]]
+        local oc = h[2] --[[@as integer]]
+        local ns_ = h[3] --[[@as integer]]
+        local nc = h[4] --[[@as integer]]
+        local typ ---@type ow.Git.Hunks.HunkType
+        if oc == 0 then
+            typ = "add"
+        elseif nc == 0 then
+            typ = "delete"
+        else
+            typ = "change"
+        end
+        local old = {}
+        if typ ~= "add" then
+            for i = os_, os_ + oc - 1 do
+                table.insert(old, old_lines[i] or "")
+            end
+        end
+        local new = {}
+        if typ ~= "delete" then
+            for i = ns_, ns_ + nc - 1 do
+                table.insert(new, new_lines[i] or "")
+            end
+        end
+        table.insert(hunks, {
+            old_start = os_,
+            old_count = oc,
+            new_start = ns_,
+            new_count = nc,
+            type = typ,
+            old_lines = old,
+            new_lines = new,
+        })
+    end
+    return hunks
+end
+
+---@type table<ow.Git.Hunks.HunkType, string>
+local DEFAULT_SIGNS = { add = "┃", change = "┃", delete = "▁" }
+
+---@return table<ow.Git.Hunks.HunkType, string>
+local function resolve_signs()
+    local cfg = vim.g.git_hunk_signs
+    if type(cfg) ~= "table" then
+        return DEFAULT_SIGNS
+    end
+    return vim.tbl_extend("force", DEFAULT_SIGNS, cfg)
+end
+
+---@type table<ow.Git.Hunks.HunkType, string>
+local SIGN_HL = {
+    add = "GitHunkAdded",
+    change = "GitHunkChanged",
+    delete = "GitHunkRemoved",
+}
+
+---@type table<ow.Git.Hunks.HunkType, string>
+local STAGED_SIGN_HL = {
+    add = "GitHunkStagedAdded",
+    change = "GitHunkStagedChanged",
+    delete = "GitHunkStagedRemoved",
+}
+
+---@param h ow.Git.Hunks.Hunk
+---@param line_count integer
+---@return integer[]  0-indexed buffer rows for the hunk
+local function hunk_rows(h, line_count)
+    if h.type == "delete" then
+        local row = math.max(h.new_start, 1) - 1
+        if row >= line_count then
+            row = math.max(line_count - 1, 0)
+        end
+        return { row }
+    end
+    local rows = {}
+    for r = h.new_start, h.new_start + h.new_count - 1 do
+        local row = r - 1
+        if row >= 0 and row < line_count then
+            table.insert(rows, row)
+        end
+    end
+    return rows
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@return integer  1-indexed last index line the hunk occupies
+local function index_end(h)
+    if h.old_count == 0 then
+        return h.old_start
+    end
+    return h.old_start + h.old_count - 1
+end
+
+---@param unstaged ow.Git.Hunks.Hunk[]
+---@param iline integer  1-indexed index line
+---@return integer?  1-indexed buffer line
+local function index_to_buffer(unstaged, iline)
+    local delta = 0
+    for _, h in ipairs(unstaged) do
+        if
+            h.old_count > 0
+            and iline >= h.old_start
+            and iline <= index_end(h)
+        then
+            return nil
+        end
+        if iline > index_end(h) then
+            delta = delta + h.new_count - h.old_count
+        end
+    end
+    return iline + delta
+end
+
+---@param state ow.Git.Hunks.BufState
+---@param line_count integer
+---@return { row: integer, hunk: ow.Git.Hunks.Hunk }[]  row is a 0-indexed buffer row
+local function staged_signs(state, line_count)
+    local out = {}
+    for _, h in ipairs(state.staged) do
+        local index_lines = {}
+        if h.type == "delete" then
+            table.insert(index_lines, math.max(h.new_start, 1))
+        else
+            for i = h.new_start, h.new_start + h.new_count - 1 do
+                table.insert(index_lines, i)
+            end
+        end
+        for _, iline in ipairs(index_lines) do
+            local bline = index_to_buffer(state.hunks, iline)
+            if bline then
+                local row = math.min(math.max(bline - 1, 0), line_count - 1)
+                table.insert(out, { row = row, hunk = h })
+            end
+        end
+    end
+    return out
+end
+
+---@param buf integer
+local function render_signs(buf)
+    if not vim.api.nvim_buf_is_valid(buf) then
+        return
+    end
+    vim.api.nvim_buf_clear_namespace(buf, NS_SIGNS, 0, -1)
+    local state = states[buf]
+    if not state or state.overlay then
+        return
+    end
+    local signs = resolve_signs()
+    local line_count = vim.api.nvim_buf_line_count(buf)
+    local signed = {}
+    for _, h in ipairs(state.hunks) do
+        for _, row in ipairs(hunk_rows(h, line_count)) do
+            signed[row] = true
+            pcall(vim.api.nvim_buf_set_extmark, buf, NS_SIGNS, row, 0, {
+                sign_text = signs[h.type],
+                sign_hl_group = SIGN_HL[h.type],
+                priority = 100,
+            })
+        end
+    end
+    for _, s in ipairs(staged_signs(state, line_count)) do
+        if not signed[s.row] then
+            pcall(vim.api.nvim_buf_set_extmark, buf, NS_SIGNS, s.row, 0, {
+                sign_text = signs[s.hunk.type],
+                sign_hl_group = STAGED_SIGN_HL[s.hunk.type],
+                priority = 100,
+            })
+        end
+    end
+end
+
+local SKIP_CAPTURES = { spell = true, nospell = true, conceal = true }
+
+---@param buf integer
+---@param lines string[]
+---@return table[][]?
+local function highlight_index(buf, lines)
+    if not vim.treesitter.highlighter.active[buf] then
+        return nil
+    end
+    local got, parser = pcall(vim.treesitter.get_parser, buf)
+    if not got or not parser then
+        return nil
+    end
+    local lang = parser:lang()
+    local query = vim.treesitter.query.get(lang, "highlights")
+    if not query then
+        return nil
+    end
+    local source = table.concat(lines, "\n")
+    local got_root, root = pcall(function()
+        local trees = vim.treesitter.get_string_parser(source, lang):parse()
+        local tree = trees and trees[1]
+        return tree and tree:root()
+    end)
+    if not got_root or not root then
+        return nil
+    end
+    ---@type table<integer, table<integer, string>>
+    local groups = {}
+    for id, node in query:iter_captures(root, source) do
+        local name = query.captures[id]
+        if name and name:sub(1, 1) ~= "_" and not SKIP_CAPTURES[name] then
+            local sr, sc, er, ec = node:range()
+            for row = sr, math.min(er, #lines - 1) do
+                local row_groups = groups[row] or {}
+                groups[row] = row_groups
+                local from = row == sr and sc or 0
+                local to = row == er and ec or #(lines[row + 1] or "")
+                for col = from, to - 1 do
+                    row_groups[col] = name
+                end
+            end
+        end
+    end
+    local out = {}
+    for row = 0, #lines - 1 do
+        local line = lines[row + 1] or ""
+        local row_groups = groups[row] or {}
+        local chunks = {}
+        local col = 0
+        while col < #line do
+            local name = row_groups[col]
+            local stop = col + 1
+            while stop < #line and row_groups[stop] == name do
+                stop = stop + 1
+            end
+            local hl ---@type string|string[]
+            if name then
+                hl = { "GitHunkDeleteLine", "@" .. name }
+            else
+                hl = "GitHunkDeleteLine"
+            end
+            table.insert(chunks, { line:sub(col + 1, stop), hl })
+            col = stop
+        end
+        out[row + 1] = chunks
+    end
+    return out
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@param hl_lines table[][]?  per-index-line syntax chunks, or nil
+---@return table[]
+local function delete_virt_lines(h, hl_lines)
+    local width = vim.o.columns
+    local virt = {}
+    for i, line in ipairs(h.old_lines) do
+        local pad = math.max(width - vim.api.nvim_strwidth(line), 0)
+        local cached = hl_lines and hl_lines[h.old_start + i - 1]
+        if cached then
+            local chunks = vim.list_extend({}, cached)
+            table.insert(chunks, {
+                string.rep(" ", pad),
+                "GitHunkDeleteLine",
+            })
+            table.insert(virt, chunks)
+        else
+            table.insert(virt, {
+                { line .. string.rep(" ", pad), "GitHunkDeleteLine" },
+            })
+        end
+    end
+    return virt
+end
+
+---@param state ow.Git.Hunks.BufState
+---@param buf integer
+---@return table[][]?
+local function index_spans(state, buf)
+    if not state.index then
+        return nil
+    end
+    local cache = state.index_hl
+    if cache and cache.src == state.index then
+        return cache.lines
+    end
+    local lines = highlight_index(buf, state.index)
+    state.index_hl = { src = state.index, lines = lines }
+    return lines
+end
+
+---@param buf integer
+local function render_overlay(buf)
+    if not vim.api.nvim_buf_is_valid(buf) then
+        return
+    end
+    vim.api.nvim_buf_clear_namespace(buf, NS_OVERLAY, 0, -1)
+    local state = states[buf]
+    if not state or not state.overlay then
+        return
+    end
+    local line_count = vim.api.nvim_buf_line_count(buf)
+    local hl_lines = index_spans(state, buf)
+    for _, h in ipairs(state.hunks) do
+        if h.type ~= "delete" then
+            for r = h.new_start, h.new_start + h.new_count - 1 do
+                local row = r - 1
+                if row >= 0 and row < line_count then
+                    pcall(
+                        vim.api.nvim_buf_set_extmark,
+                        buf,
+                        NS_OVERLAY,
+                        row,
+                        0,
+                        {
+                            line_hl_group = "GitHunkAddLine",
+                            priority = 100,
+                        }
+                    )
+                end
+            end
+        end
+        if h.type ~= "add" then
+            local row, above
+            if h.type == "delete" then
+                if h.new_start <= 0 then
+                    row, above = 0, true
+                elseif h.new_start >= line_count then
+                    row, above = math.max(line_count - 1, 0), false
+                else
+                    row, above = h.new_start, true
+                end
+            else
+                row, above = math.max(h.new_start - 1, 0), true
+            end
+            pcall(vim.api.nvim_buf_set_extmark, buf, NS_OVERLAY, row, 0, {
+                virt_lines = delete_virt_lines(h, hl_lines),
+                virt_lines_above = above,
+                right_gravity = false,
+                invalidate = true,
+            })
+        end
+    end
+end
+
+---@param buf integer
+local function render(buf)
+    render_signs(buf)
+    render_overlay(buf)
+end
+
+---@param state ow.Git.Hunks.BufState
+---@param buf integer
+---@param rev string
+---@param want string?  the wanted blob sha
+---@param have string?  the currently-loaded blob sha
+---@param apply fun(lines: string[]?, sha: string?)
+---@param after fun()
+local function ensure_content(state, buf, rev, want, have, apply, after)
+    if not want then
+        apply(nil, nil)
+        return after()
+    end
+    if want == have then
+        return after()
+    end
+    util.git({ "cat-file", "-p", rev }, {
+        cwd = state.repo.worktree,
+        silent = true,
+        on_exit = function(res)
+            if states[buf] ~= state or not vim.api.nvim_buf_is_valid(buf) then
+                return
+            end
+            if res.code == 0 then
+                apply(util.split_lines(res.stdout or ""), want)
+            else
+                apply(nil, nil)
+            end
+            after()
+        end,
+    })
+end
+
+---@param buf integer
+local function recompute(buf)
+    if not vim.api.nvim_buf_is_valid(buf) then
+        return
+    end
+    local state = states[buf]
+    if not state then
+        return
+    end
+    local r = state.repo
+    ensure_content(
+        state,
+        buf,
+        ":0:" .. state.rel,
+        r:index_sha(state.rel),
+        state.index_sha,
+        function(lines, sha)
+            state.index = lines
+            state.index_sha = sha
+        end,
+        function()
+            ensure_content(
+                state,
+                buf,
+                "HEAD:" .. state.rel,
+                r:head_sha(state.rel),
+                state.head_sha,
+                function(lines, sha)
+                    state.head = lines
+                    state.head_sha = sha
+                end,
+                function()
+                    local new =
+                        vim.api.nvim_buf_get_lines(buf, 0, -1, false)
+                    state.hunks = state.index
+                            and compute_hunks(state.index, new)
+                        or {}
+                    state.staged = state.head
+                            and state.index
+                            and compute_hunks(state.head, state.index)
+                        or {}
+                    render(buf)
+                end
+            )
+        end
+    )
+end
+
+local schedule, sched_handle = util.keyed_debounce(recompute, 100)
+
+---@param buf integer
+function M._flush(buf)
+    sched_handle.flush(buf)
+end
+
+---@param buf integer
+function M.attach(buf)
+    if states[buf] then
+        return
+    end
+    if not repo.is_worktree_buf(buf) then
+        return
+    end
+    local r = repo.find(buf)
+    if not r then
+        return
+    end
+    local rel = vim.fs.relpath(r.worktree, vim.fn.resolve(vim.api.nvim_buf_get_name(buf)))
+    if not rel then
+        return
+    end
+    ---@type ow.Git.Hunks.BufState
+    local state = {
+        repo = r,
+        rel = rel,
+        index = nil,
+        index_sha = nil,
+        head = nil,
+        head_sha = nil,
+        hunks = {},
+        staged = {},
+        overlay = vim.g.git_hunk_overlay_default == true,
+        autocmds = {},
+    }
+    states[buf] = state
+
+    local group =
+        vim.api.nvim_create_augroup("ow.git.hunks." .. buf, { clear = true })
+    table.insert(
+        state.autocmds,
+        vim.api.nvim_create_autocmd({ "TextChanged", "TextChangedI" }, {
+            group = group,
+            buffer = buf,
+            callback = function()
+                schedule(buf)
+            end,
+        })
+    )
+    table.insert(
+        state.autocmds,
+        vim.api.nvim_create_autocmd("BufWritePost", {
+            group = group,
+            buffer = buf,
+            callback = function()
+                schedule(buf)
+            end,
+        })
+    )
+
+    schedule(buf)
+end
+
+---@param buf integer
+function M.detach(buf)
+    local state = states[buf]
+    if not state then
+        return
+    end
+    if vim.api.nvim_buf_is_valid(buf) then
+        vim.api.nvim_buf_clear_namespace(buf, NS_SIGNS, 0, -1)
+        vim.api.nvim_buf_clear_namespace(buf, NS_OVERLAY, 0, -1)
+    end
+    for _, id in ipairs(state.autocmds) do
+        pcall(vim.api.nvim_del_autocmd, id)
+    end
+    pcall(vim.api.nvim_del_augroup_by_name, "ow.git.hunks." .. buf)
+    sched_handle.cancel(buf)
+    states[buf] = nil
+end
+
+---@param buf integer?
+function M.toggle_overlay(buf)
+    buf = resolve_buf(buf)
+    local state = states[buf]
+    if not state then
+        util.warning("git hunks: buffer not attached")
+        return
+    end
+    state.overlay = not state.overlay
+    render(buf)
+end
+
+---@param hunks ow.Git.Hunks.Hunk[]
+---@param row integer 1-indexed cursor line
+---@return ow.Git.Hunks.Hunk?
+local function hunk_at(hunks, row)
+    for _, h in ipairs(hunks) do
+        if h.type == "delete" then
+            if math.max(h.new_start, 1) == row then
+                return h
+            end
+        elseif row >= h.new_start and row <= h.new_start + h.new_count - 1 then
+            return h
+        end
+    end
+    return nil
+end
+
+---@param state ow.Git.Hunks.BufState
+---@param buf integer
+---@param row integer 1-indexed cursor line
+---@return ow.Git.Hunks.Hunk?
+local function staged_hunk_at(state, buf, row)
+    local line_count = vim.api.nvim_buf_line_count(buf)
+    for _, s in ipairs(staged_signs(state, line_count)) do
+        if s.row == row - 1 then
+            return s.hunk
+        end
+    end
+    return nil
+end
+
+---@param buf integer?
+---@return integer buf
+---@return ow.Git.Hunks.BufState? state
+---@return ow.Git.Hunks.Hunk? hunk
+local function cursor_hunk(buf)
+    buf = resolve_buf(buf)
+    local state = states[buf]
+    if not state then
+        return buf, nil, nil
+    end
+    return buf, state, hunk_at(state.hunks, vim.api.nvim_win_get_cursor(0)[1])
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@return integer  1-indexed buffer line to anchor the cursor on
+local function anchor_line(h)
+    if h.type == "delete" then
+        return math.max(h.new_start, 1)
+    end
+    return h.new_start
+end
+
+---@param direction "next"|"prev"
+function M.nav(direction)
+    local buf = vim.api.nvim_get_current_buf()
+    local state = states[buf]
+    if not state or #state.hunks == 0 then
+        return
+    end
+    local cur = vim.api.nvim_win_get_cursor(0)[1]
+    local hunks = state.hunks
+    local target = direction == "next" and hunks[1] or hunks[#hunks]
+    if direction == "next" then
+        for _, h in ipairs(hunks) do
+            if anchor_line(h) > cur then
+                target = h
+                break
+            end
+        end
+    else
+        for i = #hunks, 1, -1 do
+            if anchor_line(hunks[i]) < cur then
+                target = hunks[i]
+                break
+            end
+        end
+    end
+    if not target then
+        return
+    end
+    vim.api.nvim_win_set_cursor(0, { anchor_line(target), 0 })
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@return string[]
+local function hunk_body(h)
+    local lines = {
+        string.format(
+            "@@ -%d,%d +%d,%d @@",
+            h.old_start,
+            h.old_count,
+            h.new_start,
+            h.new_count
+        ),
+    }
+    for _, l in ipairs(h.old_lines) do
+        table.insert(lines, "-" .. l)
+    end
+    for _, l in ipairs(h.new_lines) do
+        table.insert(lines, "+" .. l)
+    end
+    return lines
+end
+
+local PATCH_CONTEXT = 3
+
+---@param h ow.Git.Hunks.Hunk
+---@return integer old_before  count of old lines before the hunk's changed content
+---@return integer new_before  count of new lines before the hunk's changed content
+local function hunk_offsets(h)
+    if h.type == "add" then
+        return h.old_start, h.new_start - 1
+    elseif h.type == "delete" then
+        return h.old_start - 1, h.new_start
+    end
+    return h.old_start - 1, h.new_start - 1
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@return ow.Git.Hunks.Hunk
+local function invert(h)
+    local typ ---@type ow.Git.Hunks.HunkType
+    if h.type == "add" then
+        typ = "delete"
+    elseif h.type == "delete" then
+        typ = "add"
+    else
+        typ = "change"
+    end
+    return {
+        old_start = h.new_start,
+        old_count = h.new_count,
+        new_start = h.old_start,
+        new_count = h.old_count,
+        type = typ,
+        old_lines = h.new_lines,
+        new_lines = h.old_lines,
+    }
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@param old_lines string[]
+---@param rel string
+---@return string patch
+---@return boolean zero_context
+local function build_patch(h, old_lines, rel)
+    local old_before, new_before = hunk_offsets(h)
+    local pre = {}
+    for i = math.max(old_before - PATCH_CONTEXT + 1, 1), old_before do
+        pre[#pre + 1] = old_lines[i] or ""
+    end
+    local post = {}
+    local after = old_before + h.old_count
+    for i = after + 1, math.min(after + PATCH_CONTEXT, #old_lines) do
+        post[#post + 1] = old_lines[i] or ""
+    end
+    local old_n = #pre + h.old_count + #post
+    local new_n = #pre + h.new_count + #post
+    local old_start = old_n > 0 and old_before - #pre + 1 or old_before
+    local new_start = new_n > 0 and new_before - #pre + 1 or new_before
+    local body = {
+        string.format(
+            "@@ -%d,%d +%d,%d @@",
+            old_start,
+            old_n,
+            new_start,
+            new_n
+        ),
+    }
+    for _, l in ipairs(pre) do
+        body[#body + 1] = " " .. l
+    end
+    for _, l in ipairs(h.old_lines) do
+        body[#body + 1] = "-" .. l
+    end
+    for _, l in ipairs(h.new_lines) do
+        body[#body + 1] = "+" .. l
+    end
+    for _, l in ipairs(post) do
+        body[#body + 1] = " " .. l
+    end
+    local lines = { "--- a/" .. rel, "+++ b/" .. rel }
+    vim.list_extend(lines, body)
+    return table.concat(lines, "\n") .. "\n", #pre == 0 and #post == 0
+end
+
+---@param state ow.Git.Hunks.BufState
+---@param buf integer
+---@param patch string
+---@param zero_context boolean
+local function apply_patch(state, buf, patch, zero_context)
+    local args = { "apply", "--cached" }
+    if zero_context then
+        table.insert(args, "--unidiff-zero")
+    end
+    table.insert(args, "-")
+    util.git(args, {
+        cwd = state.repo.worktree,
+        stdin = patch,
+        on_exit = function(res)
+            if res.code ~= 0 then
+                util.error("git apply failed: %s", vim.trim(res.stderr or ""))
+                return
+            end
+            local s = states[buf]
+            if s then
+                s.index_sha = nil
+                schedule(buf)
+            end
+        end,
+    })
+end
+
+---@param buf? integer
+function M.toggle_stage(buf)
+    buf = resolve_buf(buf)
+    local state = states[buf]
+    if not state then
+        return
+    end
+    local row = vim.api.nvim_win_get_cursor(0)[1]
+    local unstaged = hunk_at(state.hunks, row)
+    if unstaged and state.index then
+        local patch, zero = build_patch(unstaged, state.index, state.rel)
+        apply_patch(state, buf, patch, zero)
+        return
+    end
+    local staged = staged_hunk_at(state, buf, row)
+    if staged and state.index then
+        local patch, zero = build_patch(invert(staged), state.index, state.rel)
+        apply_patch(state, buf, patch, zero)
+        return
+    end
+    util.warning("git hunks: no hunk at cursor")
+end
+
+---@param buf? integer
+function M.reset_hunk(buf)
+    local target, state, h = cursor_hunk(buf)
+    if not state then
+        return
+    end
+    if not h then
+        util.warning("git hunks: no hunk at cursor")
+        return
+    end
+    if h.type == "add" then
+        vim.api.nvim_buf_set_lines(
+            target,
+            h.new_start - 1,
+            h.new_start - 1 + h.new_count,
+            false,
+            {}
+        )
+    elseif h.type == "delete" then
+        vim.api.nvim_buf_set_lines(
+            target,
+            h.new_start,
+            h.new_start,
+            false,
+            h.old_lines
+        )
+    else
+        vim.api.nvim_buf_set_lines(
+            target,
+            h.new_start - 1,
+            h.new_start - 1 + h.new_count,
+            false,
+            h.old_lines
+        )
+    end
+end
+
+---@param buf? integer
+function M.select_hunk(buf)
+    local _, _, h = cursor_hunk(buf)
+    if not h or h.type == "delete" then
+        return
+    end
+    local first = h.new_start
+    local last = h.new_start + math.max(h.new_count, 1) - 1
+    vim.api.nvim_win_set_cursor(0, { first, 0 })
+    vim.cmd("normal! V")
+    vim.api.nvim_win_set_cursor(0, { last, 0 })
+end
+
+local preview_win ---@type integer?
+
+---@param buf? integer
+function M.preview_hunk(buf)
+    if preview_win and vim.api.nvim_win_is_valid(preview_win) then
+        vim.api.nvim_set_current_win(preview_win)
+        return
+    end
+    local target, state, h = cursor_hunk(buf)
+    if not state then
+        return
+    end
+    if not h then
+        return
+    end
+    local lines = hunk_body(h)
+    local pbuf = vim.api.nvim_create_buf(false, true)
+    vim.api.nvim_buf_set_lines(pbuf, 0, -1, false, lines)
+    vim.bo[pbuf].filetype = "diff"
+    vim.bo[pbuf].bufhidden = "wipe"
+    local width = 0
+    for _, l in ipairs(lines) do
+        if #l > width then
+            width = #l
+        end
+    end
+    width = math.min(math.max(width + 2, 40), vim.o.columns - 4)
+    local height = math.min(#lines, math.floor(vim.o.lines / 2))
+    local win = vim.api.nvim_open_win(pbuf, false, {
+        relative = "cursor",
+        row = 1,
+        col = 0,
+        width = width,
+        height = height,
+        style = "minimal",
+    })
+    preview_win = win
+
+    local function close()
+        if vim.api.nvim_win_is_valid(win) then
+            vim.api.nvim_win_close(win, true)
+        end
+    end
+    local group =
+        vim.api.nvim_create_augroup("ow.git.hunks.preview", { clear = true })
+    vim.api.nvim_create_autocmd(
+        { "CursorMoved", "CursorMovedI", "InsertEnter" },
+        { group = group, buffer = target, callback = close }
+    )
+    vim.api.nvim_create_autocmd("WinLeave", {
+        group = group,
+        buffer = pbuf,
+        callback = close,
+    })
+    vim.api.nvim_create_autocmd("WinClosed", {
+        group = group,
+        pattern = tostring(win),
+        callback = function()
+            preview_win = nil
+            pcall(vim.api.nvim_del_augroup_by_name, "ow.git.hunks.preview")
+        end,
+    })
+    vim.keymap.set("n", "q", close, { buffer = pbuf, nowait = true })
+end
+
+repo.on("change", function(r, change)
+    for buf, state in pairs(states) do
+        if
+            state.repo == r
+            and (change.paths[state.rel] or change.branch_changed)
+        then
+            schedule(buf)
+        end
+    end
+end)
+
+for _, buf in ipairs(vim.api.nvim_list_bufs()) do
+    if vim.api.nvim_buf_is_loaded(buf) then
+        M.attach(buf)
+    end
+end
+
+return M

lua/git/log_view.lua

@@ -3,29 +3,36 @@ local util = require("git.core.util")
 
 local M = {}
 
-M.URI_PREFIX = "gitlog://"
-
 local LOG_FORMAT = "%h %ad {%an}%d %s"
 
 local cr = vim.api.nvim_replace_termcodes("<CR>", true, false, true)
 
 ---@param buf integer
-local function attach_dispatch(buf)
+---@return boolean opened
-    vim.keymap.set("n", "<CR>", function()
+local function open_under_cursor(buf)
     local r = repo.resolve(buf)
     -- Anchor past the leading graph chars (matches the leading sha column,
     -- not any hex word that happens to appear later in the subject).
     local sha = r
-            and vim.api
+        and vim.api.nvim_get_current_line():match("^[*|/\\_ ]*(%x%x%x%x%x%x%x+)")
-                .nvim_get_current_line()
+    if not sha then
-                :match("^[*|/\\_ ]*(%x%x%x%x%x%x%x+)")
+        return false
-        if sha then
+    end
     ---@cast r -nil
     require("git.object").open(r, sha, { split = false })
-        else
+    return true
+end
+
+---@param buf integer
+local function attach_dispatch(buf)
+    vim.keymap.set("n", "<CR>", function()
+        if not open_under_cursor(buf) then
             vim.api.nvim_feedkeys(cr, "n", false)
         end
     end, { buffer = buf, silent = true, desc = "Open commit" })
+    vim.keymap.set("n", "gd", function()
+        open_under_cursor(buf)
+    end, { buffer = buf, silent = true, desc = "Open commit" })
 end
 
 ---@param worktree string
@@ -56,50 +63,7 @@ local function populate(buf, r)
     if not stdout then
         return
     end
-    local new_lines = util.split_lines(stdout)
+    util.set_buf_lines(buf, 0, -1, util.split_lines(stdout))
-    local old_str = table.concat(
-        vim.api.nvim_buf_get_lines(buf, 0, -1, false),
-        "\n"
-    ) .. "\n"
-    local new_str = table.concat(new_lines, "\n") .. "\n"
-    local hunks = vim.text.diff(old_str, new_str, {
-        result_type = "indices",
-        algorithm = "histogram",
-    })
-    ---@cast hunks [integer, integer, integer, integer][]
-    if #hunks == 0 then
-        return
-    end
-    for i = #hunks, 1, -1 do
-        local sa, ca, sb, cb = unpack(hunks[i])
-        local start = ca == 0 and sa or sa - 1
-        util.set_buf_lines(
-            buf,
-            start,
-            start + ca,
-            vim.list_slice(new_lines, sb, sb + cb - 1)
-        )
-    end
-end
-
----@param buf integer
-function M.read_uri(buf)
-    local name = vim.api.nvim_buf_get_name(buf)
-    local worktree = name:sub(#M.URI_PREFIX + 1)
-    if worktree == "" then
-        return
-    end
-    local r = repo.resolve(worktree)
-    if not r then
-        return
-    end
-    repo.bind(buf, r)
-
-    util.setup_scratch(buf, { bufhidden = "hide" })
-    vim.bo[buf].filetype = "gitlog"
-
-    attach_dispatch(buf)
-    populate(buf, r)
 end
 
 ---@class ow.Git.Log.OpenOpts
@@ -120,19 +84,25 @@ function M.open(opts)
     end
 
     max_counts[r.worktree] = opts.max_count
-    local buf = vim.fn.bufadd(M.URI_PREFIX .. r.worktree)
+    local buf = vim.fn.bufadd(r.worktree .. "/GitLog")
-    local was_loaded = vim.api.nvim_buf_is_loaded(buf)
 
-    local win = vim.fn.bufwinid(buf)
+    local visible = vim.fn.bufwinid(buf)
-    if win == -1 then
+    if visible ~= -1 then
-        util.place_buf(buf, nil)
+        vim.api.nvim_set_current_win(visible)
-    else
-        vim.api.nvim_set_current_win(win)
-    end
-
-    if was_loaded then
         populate(buf, r)
+        vim.api.nvim_win_set_cursor(visible, { 1, 0 })
+        return
     end
+
+    vim.fn.bufload(buf)
+    repo.bind(buf, r)
+    util.setup_scratch(buf, { bufhidden = "hide" })
+    vim.bo[buf].filetype = "gitlog"
+    attach_dispatch(buf)
+
+    local win = util.place_buf(buf, nil)
+    vim.api.nvim_win_set_cursor(win, { 1, 0 })
+    populate(buf, r)
 end
 
 ---@param cmd_opts table
@@ -170,6 +140,4 @@ function M.complete_glog(arg_lead)
     return matches
 end
 
-repo.on_uri_change(M.URI_PREFIX, populate)
-
 return M

lua/git/object.lua

@@ -150,6 +150,9 @@ function M.attach_dispatch(buf)
             vim.api.nvim_feedkeys(cr, "n", false)
         end
     end, { buffer = buf, silent = true, desc = "Open file at commit" })
+    vim.keymap.set("n", "gd", function()
+        M.open_under_cursor()
+    end, { buffer = buf, silent = true, desc = "Open file at commit" })
 end
 
 ---@param r ow.Git.Repo
@@ -181,8 +184,7 @@ local function populate(buf, r, rev, state, rev_sha)
             local patch = util.git({
                 "diff-tree",
                 "-p",
-                "-m",
+                "--diff-merges=first-parent",
-                "--first-parent",
                 "--root",
                 "--no-commit-id",
                 commit_sha,
@@ -336,7 +338,7 @@ local function open_section(r, section)
     if left and right then
         vim.cmd.normal({ "m'", bang = true })
         vim.api.nvim_set_current_buf(right)
-        require("git.diff").split({
+        require("git.diffsplit").open({
             target = vim.api.nvim_buf_get_name(left),
             mods = { vertical = true },
         })

lua/git/status_view.lua

@@ -1,5 +1,5 @@
 local Revision = require("git.core.revision")
-local diff = require("git.diff")
+local diffsplit = require("git.diffsplit")
 local object = require("git.object")
 local repo = require("git.core.repo")
 local status = require("git.core.status")
@@ -7,8 +7,6 @@ local util = require("git.core.util")
 
 local M = {}
 
-M.URI_PREFIX = "gitstatus://"
-
 ---@type ow.Git.StatusView.Placement[]
 M.PLACEMENTS = { "sidebar", "split", "current" }
 
@@ -16,14 +14,10 @@ M.PLACEMENTS = { "sidebar", "split", "current" }
 local SECTIONS = { "untracked", "unstaged", "staged", "unmerged" }
 local WINDOW_WIDTH = 50
 
----@param name string
+---@param r ow.Git.Repo
----@return integer? bufnr
+---@return string
-local function find_buf(name)
+local function buf_name_for(r)
-    for _, b in ipairs(vim.api.nvim_list_bufs()) do
+    return r.worktree .. "/GitStatus"
-        if vim.api.nvim_buf_get_name(b) == name then
-            return b
-        end
-    end
 end
 
 ---@alias ow.Git.StatusView.Placement "sidebar"|"split"|"current"
@@ -405,12 +399,15 @@ local function view_row(s, row, focus_left)
     local older = left.name or vim.api.nvim_buf_get_name(left.buf)
     local left_win
     vim.api.nvim_win_call(target, function()
-        diff.split({
+        diffsplit.open({
             target = older,
             mods = { vertical = true },
         })
         left_win = vim.api.nvim_get_current_win()
+        vim.api.nvim_win_set_cursor(left_win, { 1, 0 })
+        vim.api.nvim_win_set_cursor(target, { 1, 0 })
     end)
+    ---@cast left_win -nil
     vim.api.nvim_set_current_win(focus_left and left_win or status_win)
 end
 
@@ -697,8 +694,9 @@ function M.open(opts)
         util.error("not in a git repository")
         return
     end
+
     local previous_win = vim.api.nvim_get_current_win()
-    local buf = vim.fn.bufadd(M.URI_PREFIX .. r.worktree)
+    local buf = vim.fn.bufadd(buf_name_for(r))
 
     local visible = vim.fn.bufwinid(buf)
     if visible ~= -1 then
@@ -707,78 +705,24 @@ function M.open(opts)
         return
     end
 
-    local was_loaded = vim.api.nvim_buf_is_loaded(buf)
+    if not state[buf] then
-    local win = place(buf, placement)
+        vim.fn.bufload(buf)
-
+        repo.bind(buf, r)
-    vim.bo[buf].bufhidden = placement == "sidebar" and "wipe" or "hide"
+        util.setup_scratch(buf, {})
-    local s = state[buf]
+        vim.bo[buf].filetype = "gitstatus"
-    if s then
+        setup_buffer(buf, r, placement)
-        s.win = win
-        s.placement = placement
     end
+    vim.bo[buf].bufhidden = placement == "sidebar" and "wipe" or "hide"
+
+    local win = place(buf, placement)
+    state[buf].win = win
+    state[buf].placement = placement
     set_keymaps(buf, placement)
 
     if placement == "sidebar" then
         vim.api.nvim_set_current_win(previous_win)
     end
 
-    if was_loaded then
-        refresh(buf)
-    end
-    r:refresh()
-end
-
----@param buf integer
-function M.read_uri(buf)
-    local name = vim.api.nvim_buf_get_name(buf)
-    local raw = name:sub(#M.URI_PREFIX + 1)
-    if raw == "" then
-        return
-    end
-    local worktree = vim.fs.abspath(raw)
-    local r = repo.resolve(worktree)
-    if not r then
-        util.error("not a git worktree: %s", raw)
-        return
-    end
-    if r.worktree ~= worktree then
-        util.warning("%s is not a worktree root, using %s", raw, r.worktree)
-    end
-    local canonical = M.URI_PREFIX .. r.worktree
-    if name ~= canonical then
-        local existing = find_buf(canonical)
-        if existing and existing ~= buf then
-            local win = vim.api.nvim_get_current_win()
-            if vim.api.nvim_win_get_buf(win) == buf then
-                vim.api.nvim_win_set_buf(win, existing)
-            end
-            vim.api.nvim_buf_delete(buf, { force = true })
-            local s = state[existing]
-            if s then
-                s.win = win
-                s.placement = "current"
-            end
-            refresh(existing)
-            r:refresh()
-            return
-        end
-        pcall(vim.api.nvim_buf_set_name, buf, canonical)
-    end
-    repo.bind(buf, r)
-
-    util.setup_scratch(buf, { bufhidden = "hide" })
-    vim.bo[buf].filetype = "gitstatus"
-
-    ---@type integer?
-    local win = vim.fn.bufwinid(buf)
-    if win == -1 then
-        win = nil
-    end
-    if not state[buf] then
-        setup_buffer(buf, r, "current", win)
-    else
-        state[buf].win = win
-    end
     refresh(buf)
     r:refresh()
 end

nvim-pack-lock.json

@@ -134,6 +134,10 @@
       "rev": "ae5199db47757f785e43a14b332118a5474de1a2",
       "src": "https://github.com/tree-sitter-grammars/tree-sitter-svelte"
     },
+    "tree-sitter-tumblr": {
+      "rev": "45938c25e96351adf4140dce42795e61e944904e",
+      "src": "https://git.owall.dev/warg/tree-sitter-tumblr.git"
+    },
     "tree-sitter-typescript": {
       "rev": "75b3874edb2dc714fb1fd77a32013d0f8699989f",
       "src": "https://github.com/tree-sitter/tree-sitter-typescript"
@@ -149,6 +153,14 @@
     "tree-sitter-zsh": {
       "rev": "86b37f8d515a529722411bc7bf3c9e993a4743bf",
       "src": "https://github.com/georgeharker/tree-sitter-zsh"
+    },
+    "vim-flog": {
+      "rev": "665b16ac8915f746bc43c9572b4581a5e9047216",
+      "src": "https://github.com/rbong/vim-flog"
+    },
+    "vim-fugitive": {
+      "rev": "3b753cf8c6a4dcde6edee8827d464ba9b8c4a6f0",
+      "src": "https://github.com/tpope/vim-fugitive"
     }
   }
 }

plugin/git.lua

@@ -34,17 +34,59 @@ local DEFAULT_HIGHLIGHTS = {
     GitUnmergedBothModified = "GitUnmerged",
     GitUnmergedDeletedByThem = "GitUnmerged",
     GitUnmergedDeletedByUs = "GitUnmerged",
+
+    GitHunkAdded = "Added",
+    GitHunkChanged = "Changed",
+    GitHunkRemoved = "Removed",
+    GitHunkAddLine = "DiffAdd",
+    GitHunkDeleteLine = "DiffDelete",
 }
+local STAGED_HUNK_HL = {
+    GitHunkStagedAdded = "GitHunkAdded",
+    GitHunkStagedChanged = "GitHunkChanged",
+    GitHunkStagedRemoved = "GitHunkRemoved",
+}
+
+local function blend(a, b, t)
+    local function mix(shift)
+        local x = bit.band(bit.rshift(a, shift), 0xff)
+        local y = bit.band(bit.rshift(b, shift), 0xff)
+        return bit.lshift(math.floor(x + (y - x) * t + 0.5), shift)
+    end
+    return mix(16) + mix(8) + mix(0)
+end
+
+local function apply_highlights()
     for name, link in pairs(DEFAULT_HIGHLIGHTS) do
         vim.api.nvim_set_hl(0, name, { link = link, default = true })
     end
+    local bg = vim.api.nvim_get_hl(0, { name = "Normal" }).bg or 0x000000
+    for name, base in pairs(STAGED_HUNK_HL) do
+        local src = vim.api.nvim_get_hl(0, { name = base, link = false })
+        local hl = {}
+        if src.fg then
+            hl.fg = blend(src.fg, bg, 0.45)
+        end
+        if src.bg then
+            hl.bg = blend(src.bg, bg, 0.45)
+        end
+        vim.api.nvim_set_hl(0, name, hl)
+    end
+end
+apply_highlights()
 
 local group = vim.api.nvim_create_augroup("ow.git", { clear = true })
 
+vim.api.nvim_create_autocmd("ColorScheme", {
+    group = group,
+    callback = apply_highlights,
+})
+
 vim.api.nvim_create_autocmd({ "BufReadPost", "BufNewFile" }, {
     group = group,
     callback = function(args)
         require("git.core.repo").track(args.buf)
+        require("git.hunks").attach(args.buf)
     end,
 })
 vim.api.nvim_create_autocmd({ "BufWritePost", "FileChangedShellPost" }, {
@@ -64,6 +106,7 @@ vim.api.nvim_create_autocmd({ "ShellCmdPost", "TermLeave", "FocusGained" }, {
 vim.api.nvim_create_autocmd({ "BufDelete", "BufWipeout" }, {
     group = group,
     callback = function(args)
+        require("git.hunks").detach(args.buf)
         require("git.core.repo").unbind(args.buf)
     end,
 })
@@ -96,21 +139,6 @@ vim.api.nvim_create_autocmd("BufReadCmd", {
         require("git.object").read_uri(args.buf)
     end,
 })
-vim.api.nvim_create_autocmd("BufReadCmd", {
-    pattern = "gitlog://*",
-    group = group,
-    callback = function(args)
-        require("git.log_view").read_uri(args.buf)
-    end,
-})
-vim.api.nvim_create_autocmd("BufReadCmd", {
-    pattern = "gitstatus://*",
-    group = group,
-    callback = function(args)
-        require("git.status_view").read_uri(args.buf)
-    end,
-})
-
 vim.api.nvim_create_user_command("G", function(opts)
     local cmd = require("git.cmd")
     cmd.run(cmd.parse_args(opts.args), { bang = opts.bang })
@@ -153,7 +181,7 @@ vim.api.nvim_create_user_command("Gdiffsplit", function(opts)
         mods = { vertical = false }
         rev_idx = 2
     end
-    require("git.diff").split({ target = fargs[rev_idx], mods = mods })
+    require("git.diffsplit").open({ target = fargs[rev_idx], mods = mods })
 end, {
     nargs = "*",
     complete = function(arg_lead, cmd_line, _)
@@ -214,25 +242,28 @@ vim.keymap.set("n", "<Plug>(git-edit)", function()
     })
 end, { silent = true, desc = "Edit a git object" })
 
-vim.keymap.set("n", "<Plug>(git-diff-vertical)", function()
+vim.keymap.set("n", "<Plug>(git-diffsplit-vertical)", function()
-    require("git.diff").split({ mods = { vertical = true } })
+    require("git.diffsplit").open({ mods = { vertical = true } })
-end, { silent = true, desc = "Diff against index (vertical)" })
+end, { silent = true, desc = "Open a diff split against index (vertical)" })
-vim.keymap.set("n", "<Plug>(git-diff-horizontal)", function()
+vim.keymap.set("n", "<Plug>(git-diffsplit-horizontal)", function()
-    require("git.diff").split({ mods = { vertical = false } })
+    require("git.diffsplit").open({ mods = { vertical = false } })
-end, { silent = true, desc = "Diff against index (horizontal)" })
+end, { silent = true, desc = "Open a diff split against index (horizontal)" })
-vim.keymap.set("n", "<Plug>(git-diff-vertical-head)", function()
+vim.keymap.set("n", "<Plug>(git-diffsplit-vertical-head)", function()
-    require("git.diff").split({
+    require("git.diffsplit").open({
         target = "HEAD",
         mods = { vertical = true },
     })
-end, { silent = true, desc = "Diff against HEAD (vertical)" })
+end, { silent = true, desc = "Open a diff split against HEAD (vertical)" })
-vim.keymap.set("n", "<Plug>(git-diff-horizontal-head)", function()
+vim.keymap.set("n", "<Plug>(git-diffsplit-horizontal-head)", function()
-    require("git.diff").split({
+    require("git.diffsplit").open({
         target = "HEAD",
         mods = { vertical = false },
     })
-end, { silent = true, desc = "Diff against HEAD (horizontal)" })
+end, { silent = true, desc = "Open a diff split against HEAD (horizontal)" })
 
+vim.keymap.set("n", "<Plug>(git-status-open)", function()
+    require("git.status_view").open()
+end, { silent = true, desc = "Open git status sidebar" })
 vim.keymap.set("n", "<Plug>(git-status-toggle)", function()
     require("git.status_view").toggle()
 end, { silent = true, desc = "Toggle git status sidebar" })
@@ -257,3 +288,29 @@ if vim.g.git_statusline ~= false then
         end,
     })
 end
+
+vim.keymap.set({ "n", "x" }, "<Plug>(git-hunk-next)", function()
+    require("git.hunks").nav("next")
+end, { silent = true, desc = "Jump to next git hunk" })
+vim.keymap.set({ "n", "x" }, "<Plug>(git-hunk-prev)", function()
+    require("git.hunks").nav("prev")
+end, { silent = true, desc = "Jump to previous git hunk" })
+vim.keymap.set("n", "<Plug>(git-hunk-stage-toggle)", function()
+    require("git.hunks").toggle_stage()
+end, { silent = true, desc = "Stage or unstage the hunk under cursor" })
+vim.keymap.set("n", "<Plug>(git-hunk-reset)", function()
+    require("git.hunks").reset_hunk()
+end, { silent = true, desc = "Reset hunk under cursor" })
+vim.keymap.set("n", "<Plug>(git-hunk-preview)", function()
+    require("git.hunks").preview_hunk()
+end, { silent = true, desc = "Preview hunk under cursor" })
+vim.keymap.set("n", "<Plug>(git-hunk-select)", function()
+    require("git.hunks").select_hunk()
+end, { silent = true, desc = "Select hunk under cursor" })
+vim.keymap.set("n", "<Plug>(git-overlay-toggle)", function()
+    require("git.hunks").toggle_overlay()
+end, { silent = true, desc = "Toggle the git diff overlay" })
+
+vim.api.nvim_create_user_command("GitDiffOverlay", function()
+    require("git.hunks").toggle_overlay()
+end, { desc = "Toggle the git diff overlay in the current buffer" })

plugins/gitsigns.lua

@@ -1,48 +0,0 @@
-require("gitsigns").setup({
-    preview_config = {
-        border = "single",
-    },
-    on_attach = function(bufnr)
-        local gs = require("gitsigns")
-        vim.keymap.set("n", "<leader>gv", gs.select_hunk, { buffer = bufnr })
-        vim.keymap.set("n", "<leader>gs", gs.stage_hunk, { buffer = bufnr })
-        vim.keymap.set("x", "<leader>gs", function()
-            gs.stage_hunk({ vim.fn.line("."), vim.fn.line("v") })
-        end, { buffer = bufnr })
-        vim.keymap.set("n", "<leader>gr", gs.reset_hunk, { buffer = bufnr })
-        vim.keymap.set(
-            "x",
-            "<leader>gr",
-            ":Gitsigns reset_hunk<CR>",
-            { buffer = bufnr }
-        )
-        vim.keymap.set("n", "<leader>g?", gs.preview_hunk, { buffer = bufnr })
-        vim.keymap.set("n", "<leader>gb", function()
-            gs.blame_line({ full = true, ignore_whitespace = true })
-        end, { buffer = bufnr })
-        vim.keymap.set({ "n", "x" }, "]g", function()
-            gs.nav_hunk("next", {
-                wrap = true,
-                foldopen = true,
-                navigation_message = true,
-                greedy = true,
-                preview = true,
-                count = 1,
-                target = "all",
-            })
-        end)
-        vim.keymap.set({ "n", "x" }, "[g", function()
-            gs.nav_hunk("prev", {
-                wrap = true,
-                foldopen = true,
-                navigation_message = true,
-                greedy = true,
-                preview = true,
-                count = 1,
-                target = "all",
-            })
-        end)
-    end,
-    attach_to_untracked = false,
-    sign_priority = 100,
-})

plugins/onedark.lua

@@ -45,10 +45,8 @@ local highlights = {
     TabLineFill = { bg = c.bg1 },
     EndOfBuffer = { fg = "NONE", bg = "NONE" },
     DiffAdd = { bg = "#1a2f22" },
-    DiffChange = { bg = "#15304a" },
-    DiffDelete = { bg = "#311c1e" },
-    Changed = { fg = c.yellow },
     NvimTreeIndentMarker = { fg = c.bg3 },
+    GitUnstaged = { fg = c.yellow },
 }
 for kind, color in pairs(completion_kind_colors) do
     highlights["LspKind" .. kind] = { fg = color }

test/git/cmd_test.lua

@@ -338,10 +338,10 @@ t.test("<leader>gl log buffer refills after jumping back", function()
     h.git(dir, "commit", "-q", "-m", "second")
 
     require("git.log_view").open({ max_count = 1000 })
-    wait_buf_populated("^gitlog://")
+    wait_buf_populated("/GitLog$")
     local log_buf = vim.api.nvim_get_current_buf()
     local log_win = vim.api.nvim_get_current_win()
-    t.truthy(vim.api.nvim_buf_get_name(log_buf):match("^gitlog://"))
+    t.truthy(vim.api.nvim_buf_get_name(log_buf):match("/GitLog$"))
     local initial_lines = #vim.api.nvim_buf_get_lines(log_buf, 0, -1, false)
     t.truthy(initial_lines >= 2)
 

test/git/hunks_test.lua

@@ -0,0 +1,634 @@
+local h = require("test.git.helpers")
+local hunks = require("git.hunks")
+local t = require("test")
+
+---@param committed string
+---@param worktree string
+---@param file string?
+---@return string dir
+---@return integer buf
+---@return ow.Git.Hunks.BufState state
+local function setup(committed, worktree, file)
+    file = file or "a.txt"
+    local dir = h.make_repo({ [file] = committed })
+    t.write(dir, file, worktree)
+    vim.cmd.edit(dir .. "/" .. file)
+    local buf = vim.api.nvim_get_current_buf()
+    hunks.attach(buf)
+    hunks._flush(buf)
+    t.wait_for(function()
+        local s = hunks.state(buf)
+        return s ~= nil and s.index ~= nil and s.head ~= nil
+    end, "hunks to load the index and HEAD snapshots")
+    local state = assert(hunks.state(buf), "buffer state should exist")
+    return dir, buf, state
+end
+
+---@param buf integer
+---@return { row: integer, sign: string, hl: string }[]
+local function sign_marks(buf)
+    local ns = vim.api.nvim_get_namespaces()["ow.git.hunks"]
+    local out = {}
+    for _, m in ipairs(vim.api.nvim_buf_get_extmarks(buf, ns, 0, -1, {
+        details = true,
+    })) do
+        local d = assert(m[4])
+        table.insert(out, {
+            row = m[2],
+            sign = vim.trim(d.sign_text or ""),
+            hl = d.sign_hl_group,
+        })
+    end
+    table.sort(out, function(a, b)
+        return a.row < b.row
+    end)
+    return out
+end
+
+---@param buf integer
+---@param ns_name string
+---@return vim.api.keyset.get_extmark_item[]
+local function detailed_marks(buf, ns_name)
+    local ns = vim.api.nvim_get_namespaces()[ns_name]
+    return vim.api.nvim_buf_get_extmarks(buf, ns, 0, -1, { details = true })
+end
+
+---@return integer?
+local function find_float()
+    for _, w in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
+        if vim.api.nvim_win_get_config(w).relative ~= "" then
+            return w
+        end
+    end
+end
+
+t.test("pure add: hunk shape and add signs", function()
+    local _, buf, state = setup("a\nd\n", "a\nb\nc\nd\n")
+    t.eq(#state.hunks, 1, "one hunk for a pure addition")
+    local hk = assert(state.hunks[1])
+    t.eq(hk.type, "add")
+    t.eq(hk.new_start, 2)
+    t.eq(hk.new_count, 2)
+    t.eq(sign_marks(buf), {
+        { row = 1, sign = "┃", hl = "GitHunkAdded" },
+        { row = 2, sign = "┃", hl = "GitHunkAdded" },
+    })
+end)
+
+t.test("pure delete (middle): hunk shape and delete sign", function()
+    local _, buf, state = setup("a\nb\nc\n", "a\nc\n")
+    t.eq(#state.hunks, 1)
+    local hk = assert(state.hunks[1])
+    t.eq(hk.type, "delete")
+    t.eq(hk.new_count, 0)
+    t.eq(hk.old_lines, { "b" })
+    t.eq(sign_marks(buf), {
+        { row = 0, sign = "▁", hl = "GitHunkRemoved" },
+    })
+end)
+
+t.test("top-of-file delete: sign anchors on line 1", function()
+    local _, buf, state = setup("a\nb\nc\n", "b\nc\n")
+    t.eq(#state.hunks, 1)
+    local hk = assert(state.hunks[1])
+    t.eq(hk.type, "delete")
+    t.eq(hk.new_start, 0)
+    t.eq(hk.old_lines, { "a" })
+    t.eq(sign_marks(buf), {
+        { row = 0, sign = "▁", hl = "GitHunkRemoved" },
+    })
+end)
+
+t.test("change of N lines: hunk shape and change signs", function()
+    local _, buf, state = setup("a\nb\nc\nd\n", "a\nB\nC\nd\n")
+    t.eq(#state.hunks, 1)
+    local hk = assert(state.hunks[1])
+    t.eq(hk.type, "change")
+    t.eq(hk.old_start, 2)
+    t.eq(hk.old_count, 2)
+    t.eq(hk.new_start, 2)
+    t.eq(hk.new_count, 2)
+    t.eq(hk.old_lines, { "b", "c" })
+    t.eq(hk.new_lines, { "B", "C" })
+    t.eq(sign_marks(buf), {
+        { row = 1, sign = "┃", hl = "GitHunkChanged" },
+        { row = 2, sign = "┃", hl = "GitHunkChanged" },
+    })
+end)
+
+t.test("multi-hunk file: two separate change hunks", function()
+    local _, buf, state = setup("a\nb\nc\nd\ne\n", "A\nb\nc\nd\nE\n")
+    t.eq(#state.hunks, 2, "two hunks for two disjoint changes")
+    t.eq(sign_marks(buf), {
+        { row = 0, sign = "┃", hl = "GitHunkChanged" },
+        { row = 4, sign = "┃", hl = "GitHunkChanged" },
+    })
+end)
+
+t.test("clean file produces no hunks or signs", function()
+    local _, buf, state = setup("a\nb\nc\n", "a\nb\nc\n")
+    t.eq(#state.hunks, 0)
+    t.eq(sign_marks(buf), {})
+end)
+
+t.test("editing the buffer refreshes signs", function()
+    local _, buf, state = setup("a\nb\nc\n", "a\nb\nc\n")
+    t.eq(#state.hunks, 0)
+    vim.api.nvim_buf_set_lines(buf, 1, 2, false, { "CHANGED" })
+    vim.api.nvim_exec_autocmds("TextChanged", { buffer = buf })
+    hunks._flush(buf)
+    t.wait_for(function()
+        local s = assert(hunks.state(buf))
+        return #s.hunks == 1
+    end, "hunks to pick up the in-buffer edit")
+    local hk = assert(assert(hunks.state(buf)).hunks[1])
+    t.eq(hk.type, "change")
+end)
+
+t.test("overlay: change hunk shows deletion and addition", function()
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    hunks.toggle_overlay(buf)
+    ---@type integer?
+    local add_row
+    ---@type vim.api.keyset.extmark_details?
+    local add_d
+    ---@type vim.api.keyset.extmark_details?
+    local virt_d
+    for _, m in ipairs(detailed_marks(buf, "ow.git.hunks.overlay")) do
+        local d = assert(m[4])
+        if d.line_hl_group then
+            add_row, add_d = m[2], d
+        elseif d.virt_lines then
+            virt_d = d
+        end
+    end
+    add_d = assert(add_d, "the added line should get a line highlight")
+    t.eq(add_row, 1, "addition highlighted on the changed line")
+    t.eq(add_d.line_hl_group, "GitHunkAddLine")
+    virt_d = assert(virt_d, "the deletion should render as virtual lines")
+    local piece = assert(assert(assert(virt_d.virt_lines)[1])[1])
+    t.truthy(vim.startswith(piece[1], "b"), "deleted line shows the old content")
+    t.eq(piece[2], "GitHunkDeleteLine")
+end)
+
+t.test("overlay: delete hunk shows only deletion lines", function()
+    local _, buf = setup("a\nb\nc\n", "a\nc\n")
+    hunks.toggle_overlay(buf)
+    local marks = detailed_marks(buf, "ow.git.hunks.overlay")
+    t.eq(#marks, 1, "a pure delete has no addition highlight")
+    local d = assert(assert(marks[1])[4])
+    local piece = assert(assert(assert(d.virt_lines)[1])[1])
+    t.truthy(vim.startswith(piece[1], "b"))
+    t.eq(piece[2], "GitHunkDeleteLine")
+end)
+
+t.test("overlay: add hunk highlights the added lines", function()
+    local _, buf = setup("a\nd\n", "a\nb\nc\nd\n")
+    hunks.toggle_overlay(buf)
+    local rows = {}
+    for _, m in ipairs(detailed_marks(buf, "ow.git.hunks.overlay")) do
+        local d = assert(m[4])
+        t.falsy(d.virt_lines, "a pure add has no deletion virtual lines")
+        t.eq(d.line_hl_group, "GitHunkAddLine")
+        table.insert(rows, m[2])
+    end
+    table.sort(rows)
+    t.eq(rows, { 1, 2 }, "both added lines highlighted")
+end)
+
+t.test("overlay: deleted lines are treesitter-highlighted", function()
+    local _, buf = setup(
+        "-- a note\nlocal x = 1\nlocal y = 2\n",
+        "local y = 2\n",
+        "a.lua"
+    )
+    t.truthy(
+        pcall(vim.treesitter.start, buf, "lua"),
+        "the lua parser should be available"
+    )
+    hunks.toggle_overlay(buf)
+    ---@type table[]?
+    local virt
+    for _, m in ipairs(detailed_marks(buf, "ow.git.hunks.overlay")) do
+        local d = assert(m[4])
+        if d.virt_lines then
+            virt = d.virt_lines
+        end
+    end
+    virt = assert(virt, "a deletion virtual line should render")
+    ---@type table<string, boolean>
+    local seen = {}
+    for _, line in ipairs(virt) do
+        for _, c in ipairs(line) do
+            local hl = c[2]
+            if
+                type(hl) == "table"
+                and hl[1] == "GitHunkDeleteLine"
+                and hl[2]
+            then
+                seen[hl[2]] = true
+            end
+        end
+    end
+    t.truthy(seen["@comment"], "the deleted comment keeps its @comment group")
+    t.truthy(seen["@keyword"], "deleted code keeps its syntax groups")
+end)
+
+t.test("overlay: toggling swaps gutter signs for the overlay", function()
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    t.truthy(
+        #detailed_marks(buf, "ow.git.hunks") > 0,
+        "gutter signs present while the overlay is off"
+    )
+    t.eq(#detailed_marks(buf, "ow.git.hunks.overlay"), 0)
+
+    hunks.toggle_overlay(buf)
+    t.truthy(
+        #detailed_marks(buf, "ow.git.hunks.overlay") > 0,
+        "overlay present once it is on"
+    )
+    t.eq(
+        #detailed_marks(buf, "ow.git.hunks"),
+        0,
+        "gutter signs replaced while the overlay is on"
+    )
+
+    hunks.toggle_overlay(buf)
+    t.eq(#detailed_marks(buf, "ow.git.hunks.overlay"), 0)
+    t.truthy(
+        #detailed_marks(buf, "ow.git.hunks") > 0,
+        "gutter signs restored after toggling the overlay off"
+    )
+end)
+
+t.test("toggle_stage stages the change into the index", function()
+    local dir, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "stage to land in the index")
+    t.eq(h.git(dir, "diff", "--cached", "--name-only").stdout, "a.txt")
+    t.eq(
+        h.git(dir, "show", ":0:a.txt").stdout,
+        "a\nB\nc",
+        "index blob reflects the staged change"
+    )
+end)
+
+t.test("toggle_stage stages a pure addition", function()
+    local dir, buf = setup("a\nb\n", "a\nb\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "stage to land in the index")
+    t.eq(h.git(dir, "show", ":0:a.txt").stdout, "a\nb\nc")
+end)
+
+t.test("toggle_stage stages a deletion", function()
+    local dir, buf = setup("a\nb\nc\n", "a\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "stage to land in the index")
+    t.eq(h.git(dir, "show", ":0:a.txt").stdout, "a\nc")
+end)
+
+t.test("toggle_stage stages only the hunk under the cursor", function()
+    local committed = table.concat({
+        "local M = {}",
+        "",
+        "function M.first()",
+        "    return 1",
+        "end",
+        "",
+        "function M.last()",
+        "    return 9",
+        "end",
+        "",
+        "return M",
+    }, "\n") .. "\n"
+    local worktree = table.concat({
+        "local M = {}",
+        "",
+        "-- helpers",
+        "function M.first()",
+        "    return 1",
+        "end",
+        "",
+        "function M.mid()",
+        "    return 5",
+        "end",
+        "",
+        "function M.last()",
+        "    return 9",
+        "end",
+        "",
+        "return M",
+    }, "\n") .. "\n"
+    local dir, buf = setup(committed, worktree)
+    vim.api.nvim_win_set_cursor(0, { 9, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "the mid hunk to land in the index")
+    t.eq(
+        h.git(dir, "show", ":0:a.txt").stdout,
+        table.concat({
+            "local M = {}",
+            "",
+            "function M.first()",
+            "    return 1",
+            "end",
+            "",
+            "function M.mid()",
+            "    return 5",
+            "end",
+            "",
+            "function M.last()",
+            "    return 9",
+            "end",
+            "",
+            "return M",
+        }, "\n"),
+        "only the cursor's hunk is staged, placed at the right line"
+    )
+end)
+
+t.test("toggle_stage stages a whole-file change with no context", function()
+    local dir, buf = setup("a\nb\nc\n", "x\ny\nz\n")
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "the change to land in the index")
+    t.eq(h.git(dir, "show", ":0:a.txt").stdout, "x\ny\nz")
+end)
+
+t.test("toggle_stage stages a change at the start of the file", function()
+    local dir, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nc\nd\ne\n")
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "the change to land in the index")
+    t.eq(h.git(dir, "show", ":0:a.txt").stdout, "A\nb\nc\nd\ne")
+end)
+
+t.test("toggle_stage stages a change at the end of the file", function()
+    local dir, buf = setup("a\nb\nc\nd\ne\n", "a\nb\nc\nd\nE\n")
+    vim.api.nvim_win_set_cursor(0, { 5, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "the change to land in the index")
+    t.eq(h.git(dir, "show", ":0:a.txt").stdout, "a\nb\nc\nd\nE")
+end)
+
+t.test("toggle_stage stages a deletion at the start of the file", function()
+    local dir, buf = setup("a\nb\nc\nd\n", "b\nc\nd\n")
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "the deletion to land in the index")
+    t.eq(h.git(dir, "show", ":0:a.txt").stdout, "b\nc\nd")
+end)
+
+t.test("toggle_stage leaves an adjacent unstaged hunk in place", function()
+    local dir, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nC\nd\ne\n")
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return h.git(dir, "diff", "--cached", "--name-only").stdout ~= ""
+    end, "the line-3 hunk to land in the index")
+    t.eq(
+        h.git(dir, "show", ":0:a.txt").stdout,
+        "a\nb\nC\nd\ne",
+        "only line 3 is staged; the adjacent line-1 hunk is untouched"
+    )
+end)
+
+t.test("toggle_stage unstages one of two adjacent staged hunks", function()
+    local dir, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nC\nd\ne\n")
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).staged == 1
+    end, "the line-1 hunk to be staged")
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        local s = assert(hunks.state(buf))
+        return #s.hunks == 0 and #s.staged == 2
+    end, "both hunks to be staged")
+
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).staged == 1
+    end, "the line-3 hunk to be unstaged again")
+    t.eq(
+        h.git(dir, "show", ":0:a.txt").stdout,
+        "A\nb\nc\nd\ne",
+        "line 3 reverts to HEAD while the staged line-1 change remains"
+    )
+end)
+
+t.test("toggle_stage refreshes the gutter when status stays modified", function()
+    local _, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nC\nd\nE\n")
+    t.eq(#assert(hunks.state(buf)).hunks, 3)
+
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).hunks == 2
+    end, "gutter to drop the first staged hunk")
+
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).hunks == 1
+    end, "gutter to drop the middle staged hunk")
+end)
+
+t.test("staged hunks show with the staged highlight", function()
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        local s = assert(hunks.state(buf))
+        return #s.hunks == 0 and #s.staged == 1
+    end, "the hunk to move from unstaged to staged")
+    t.eq(sign_marks(buf), {
+        { row = 1, sign = "┃", hl = "GitHunkStagedChanged" },
+    })
+end)
+
+t.test("the gutter shows staged and unstaged hunks together", function()
+    local _, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nC\nd\nE\n")
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).hunks == 2
+    end, "the first hunk to leave the unstaged set")
+    t.eq(sign_marks(buf), {
+        { row = 0, sign = "┃", hl = "GitHunkStagedChanged" },
+        { row = 2, sign = "┃", hl = "GitHunkChanged" },
+        { row = 4, sign = "┃", hl = "GitHunkChanged" },
+    })
+end)
+
+t.test("toggle_stage toggles a staged hunk back to unstaged", function()
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        local s = assert(hunks.state(buf))
+        return #s.hunks == 0 and #s.staged == 1
+    end, "the hunk to become staged")
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        local s = assert(hunks.state(buf))
+        return #s.hunks == 1 and #s.staged == 0
+    end, "the hunk to return to unstaged")
+    t.eq(sign_marks(buf), {
+        { row = 1, sign = "┃", hl = "GitHunkChanged" },
+    })
+end)
+
+t.test("toggle_stage unstages correctly when buffer lines are shifted", function()
+    local dir, buf = setup("a\nb\nc\n", "a\nb\nC\n")
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).staged == 1
+    end, "the line-3 change to be staged")
+
+    vim.api.nvim_buf_set_lines(buf, 0, 0, false, { "NEW" })
+    vim.api.nvim_exec_autocmds("TextChanged", { buffer = buf })
+    hunks._flush(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).hunks == 1
+    end, "the unstaged add at the top to register")
+
+    vim.api.nvim_win_set_cursor(0, { 4, 0 })
+    hunks.toggle_stage(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).staged == 0
+    end, "the shifted staged hunk to be unstaged")
+    t.eq(
+        h.git(dir, "show", ":0:a.txt").stdout,
+        "a\nb\nc",
+        "the index reverts to HEAD content for the unstaged hunk"
+    )
+end)
+
+t.test("reset_hunk restores the index content for a change", function()
+    local _, buf, state = setup("a\nb\nc\n", "a\nB\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.reset_hunk(buf)
+    t.eq(
+        vim.api.nvim_buf_get_lines(buf, 0, -1, false),
+        state.index,
+        "buffer matches the index after reset"
+    )
+end)
+
+t.test("reset_hunk re-inserts deleted lines", function()
+    local _, buf = setup("a\nb\nc\n", "a\nc\n")
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.reset_hunk(buf)
+    t.eq(vim.api.nvim_buf_get_lines(buf, 0, -1, false), { "a", "b", "c" })
+end)
+
+t.test("reset_hunk removes a pure addition", function()
+    local _, buf = setup("a\nd\n", "a\nb\nc\nd\n")
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.reset_hunk(buf)
+    t.eq(vim.api.nvim_buf_get_lines(buf, 0, -1, false), { "a", "d" })
+end)
+
+t.test("git_hunk_signs overrides the sign character per kind", function()
+    local prev = vim.g.git_hunk_signs
+    vim.g.git_hunk_signs = { change = "C" }
+    t.defer(function()
+        vim.g.git_hunk_signs = prev
+    end)
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    t.eq(sign_marks(buf), {
+        { row = 1, sign = "C", hl = "GitHunkChanged" },
+    })
+end)
+
+t.test("git_hunk_signs falls back to the default for unset kinds", function()
+    local prev = vim.g.git_hunk_signs
+    vim.g.git_hunk_signs = { add = "A" }
+    t.defer(function()
+        vim.g.git_hunk_signs = prev
+    end)
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    t.eq(sign_marks(buf), {
+        { row = 1, sign = "┃", hl = "GitHunkChanged" },
+    })
+end)
+
+t.test("preview_hunk shows the hunk body without file headers", function()
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    vim.api.nvim_set_current_buf(buf)
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.preview_hunk(buf)
+    local float = assert(find_float(), "preview float should open")
+    t.defer(function()
+        pcall(vim.api.nvim_win_close, float, true)
+    end)
+    local lines = vim.api.nvim_buf_get_lines(
+        vim.api.nvim_win_get_buf(float),
+        0,
+        -1,
+        false
+    )
+    t.truthy(
+        vim.startswith(lines[1] or "", "@@ "),
+        "first line is the @@ header"
+    )
+    for _, l in ipairs(lines) do
+        t.falsy(vim.startswith(l, "--- "), "no --- file header line")
+        t.falsy(vim.startswith(l, "+++ "), "no +++ file header line")
+    end
+end)
+
+t.test("preview_hunk re-invocation focuses the open float", function()
+    local _, buf = setup("a\nb\nc\n", "a\nB\nc\n")
+    vim.api.nvim_set_current_buf(buf)
+    vim.api.nvim_win_set_cursor(0, { 2, 0 })
+    hunks.preview_hunk(buf)
+    local float = assert(find_float(), "preview float should open")
+    t.defer(function()
+        pcall(vim.api.nvim_win_close, float, true)
+    end)
+    t.truthy(
+        vim.api.nvim_get_current_win() ~= float,
+        "the float opens unfocused"
+    )
+    hunks.preview_hunk(buf)
+    t.eq(
+        vim.api.nvim_get_current_win(),
+        float,
+        "re-invoking focuses the existing float"
+    )
+end)
+
+t.test("nav jumps to next and previous hunks with wrap", function()
+    local _, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nc\nd\nE\n")
+    vim.api.nvim_set_current_buf(buf)
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.nav("next")
+    t.eq(vim.api.nvim_win_get_cursor(0)[1], 5, "next hunk is line 5")
+    hunks.nav("next")
+    t.eq(vim.api.nvim_win_get_cursor(0)[1], 1, "next wraps back to line 1")
+    hunks.nav("prev")
+    t.eq(vim.api.nvim_win_get_cursor(0)[1], 5, "prev wraps back to line 5")
+end)

test/git/object_test.lua

@@ -51,7 +51,6 @@ end)
 t.test("parse_uri returns nil for non-git URIs", function()
     t.falsy(object.parse_uri("file:///tmp/x"))
     t.falsy(object.parse_uri("/tmp/x"))
-    t.falsy(object.parse_uri("gitlog:///tmp/x"))
 end)
 
 t.test("M.open(HEAD) names buffer with full sha", function()
@@ -87,6 +86,23 @@ t.test("M.open(HEAD:<path>) loads file content at HEAD", function()
     )
 end)
 
+t.test("M.open on a merge commit diffs against the first parent only", function()
+    local dir = h.make_repo({ ["a.txt"] = "one\n" })
+    t.write(dir, "a.txt", "two\n")
+    h.git(dir, "stash")
+    local stash = h.git(dir, "rev-parse", "stash@{0}").stdout
+    local r = assert(require("git.core.repo").resolve(dir))
+
+    object.open(r, stash, { split = false })
+    local count = 0
+    for _, l in ipairs(vim.api.nvim_buf_get_lines(0, 0, -1, false)) do
+        if l:match("^diff %-%-git ") then
+            count = count + 1
+        end
+    end
+    t.eq(count, 1, "the stashed file's diff appears once, not per-parent")
+end)
+
 t.test("M.open errors on a bogus base, no buffer is opened", function()
     local dir = h.make_repo({ a = "first\n" })
     local r = assert(require("git.core.repo").resolve(dir))

test/git/repo_test.lua

@@ -71,6 +71,51 @@ t.test("get_cached memoizes by key", function()
     t.truthy(v1 == v2, "second call should return cached table")
 end)
 
+t.test("index_sha returns the blob sha and caches it", function()
+    local dir = h.make_repo({ a = "x\n" })
+    local r = assert(require("git.core.repo").resolve(dir))
+    local sha = r:index_sha("a")
+    t.truthy(sha and #sha > 0, "index_sha returns the stage-0 blob sha")
+    t.truthy(r._cache["index:a"] ~= nil, "the result is cached")
+    t.eq(r:index_sha("a"), sha, "a cached call returns the same sha")
+end)
+
+t.test("index_sha caches a negative result for an untracked path", function()
+    local dir = h.make_repo({ a = "x\n" })
+    local r = assert(require("git.core.repo").resolve(dir))
+    t.eq(r:index_sha("nope"), nil, "an untracked path has no index sha")
+    t.eq(r._cache["index:nope"], false, "the negative result is cached")
+end)
+
+t.test("index_sha cache clears when the index is written", function()
+    local dir = h.make_repo({ a = "x\n" })
+    local r = assert(require("git.core.repo").resolve(dir))
+    r:index_sha("a")
+    t.truthy(r._cache["index:a"] ~= nil, "sha is cached before the stage")
+    t.write(dir, "a", "y\n")
+    h.git(dir, "add", "a")
+    wait_cleared(r, "index:a", 2000)
+end)
+
+t.test("head_sha returns the blob sha and caches it", function()
+    local dir = h.make_repo({ a = "x\n" })
+    local r = assert(require("git.core.repo").resolve(dir))
+    local sha = r:head_sha("a")
+    t.truthy(sha and #sha > 0, "head_sha returns the HEAD blob sha")
+    t.truthy(r._cache["head_blob:a"] ~= nil, "the result is cached")
+    t.eq(r:head_sha("a"), sha, "a cached call returns the same sha")
+end)
+
+t.test("head_sha cache clears when HEAD moves", function()
+    local dir = h.make_repo({ a = "x\n" })
+    local r = assert(require("git.core.repo").resolve(dir))
+    r:head_sha("a")
+    t.truthy(r._cache["head_blob:a"] ~= nil, "sha is cached before the commit")
+    t.write(dir, "a", "y\n")
+    h.git(dir, "commit", "-aqm", "change")
+    wait_cleared(r, "head_blob:a", 2000)
+end)
+
 t.test("cache clears after top-level .git change (commit)", function()
     local dir = h.make_repo({ a = "x" })
     local r = assert(require("git.core.repo").resolve(dir))

test/git/status_view_test.lua

@@ -277,7 +277,7 @@ t.test(
             error("a non-sidebar window should remain after close")
         end
         vim.api.nvim_set_current_win(remaining)
-        require("git.diff").split({ mods = { vertical = true } })
+        require("git.diffsplit").open({ mods = { vertical = true } })
         t.wait_for(function()
             local count = 0
             for _, w in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
@@ -315,3 +315,173 @@ t.test(
         )
     end
 )
+
+t.test("sidebar buffer is named <worktree>/GitStatus", function()
+    local repo = h.make_repo({ ["foo.txt"] = "x\n" })
+    vim.cmd("cd " .. repo)
+    require("git.status_view").open({ placement = "sidebar" })
+    local r = assert(require("git.core.repo").find(vim.fn.getcwd()))
+    local buf = find_sidebar()
+    assert(buf, "sidebar buffer should exist")
+    t.eq(
+        vim.api.nvim_buf_get_name(buf),
+        r.worktree .. "/GitStatus",
+        "buffer name should be <worktree>/GitStatus"
+    )
+end)
+
+t.test(
+    "calling open twice without closing focuses the existing sidebar",
+    function()
+        local repo = h.make_repo({ ["foo.txt"] = "x\n" })
+        vim.cmd("cd " .. repo)
+        require("git.status_view").open({ placement = "sidebar" })
+        local first = find_sidebar()
+        assert(first, "first sidebar buffer should exist")
+
+        require("git.status_view").open({ placement = "sidebar" })
+        local second = find_sidebar()
+        assert(second, "second sidebar buffer should exist")
+        t.eq(
+            first,
+            second,
+            "consecutive opens should reuse the visible sidebar"
+        )
+        local count = 0
+        for _, b in ipairs(vim.api.nvim_list_bufs()) do
+            if vim.bo[b].filetype == "gitstatus" then
+                count = count + 1
+            end
+        end
+        t.eq(count, 1, "only one gitstatus buffer should exist")
+    end
+)
+
+t.test("opening for different worktrees creates separate buffers", function()
+    local repo_a = h.make_repo({ ["a.txt"] = "x\n" })
+    local repo_b = h.make_repo({ ["b.txt"] = "y\n" })
+
+    vim.cmd("cd " .. repo_a)
+    require("git.status_view").open({ placement = "sidebar" })
+    local buf_a = find_sidebar()
+    require("git.status_view").toggle()
+
+    vim.cmd("cd " .. repo_b)
+    require("git.status_view").open({ placement = "sidebar" })
+    local buf_b = find_sidebar()
+
+    assert(buf_a and buf_b)
+    t.truthy(
+        buf_a ~= buf_b,
+        "different worktrees should produce different buffers"
+    )
+end)
+
+t.test("sidebar buffer is buftype=nofile and not buflisted", function()
+    local repo = h.make_repo({ ["foo.txt"] = "x\n" })
+    vim.cmd("cd " .. repo)
+    require("git.status_view").open({ placement = "sidebar" })
+    local buf = find_sidebar()
+    assert(buf, "sidebar buffer should exist")
+    t.eq(vim.bo[buf].buftype, "nofile", "buftype should be nofile")
+    t.eq(vim.bo[buf].buflisted, false, "buflisted should be false")
+end)
+
+t.test("sidebar buffer name does not get written to disk", function()
+    local repo = h.make_repo({ ["foo.txt"] = "x\n" })
+    vim.cmd("cd " .. repo)
+    require("git.status_view").open({ placement = "sidebar" })
+    local buf = find_sidebar()
+    assert(buf, "sidebar buffer should exist")
+    local name = vim.api.nvim_buf_get_name(buf)
+    vim.api.nvim_buf_call(buf, function()
+        pcall(function()
+            vim.cmd("silent! write")
+        end)
+    end)
+    t.eq(
+        vim.uv.fs_stat(name),
+        nil,
+        "no real file should be created at the sidebar buffer's path"
+    )
+end)
+
+t.test(
+    "diffsplit from sidebar resets cursor so panes stay in sync",
+    function()
+        local committed, worktree = {}, {}
+        for i = 1, 100 do
+            committed[i] = "line " .. i
+            worktree[i] = i == 10
+                    and "CHANGED " .. i
+                or i == 40 and "CHANGED " .. i
+                or i == 70 and "CHANGED " .. i
+                or i == 90 and "CHANGED " .. i
+                or ("line " .. i)
+        end
+        local repo = h.make_repo({
+            ["file.txt"] = table.concat(committed, "\n") .. "\n",
+        })
+        t.write(repo, "file.txt", table.concat(worktree, "\n") .. "\n")
+        vim.cmd("cd " .. repo)
+
+        -- Open the worktree file in a normal window and position cursor in
+        -- what becomes a folded section after diff is set up.
+        vim.cmd("edit file.txt")
+        vim.api.nvim_win_set_cursor(0, { 50, 0 })
+
+        require("git.status_view").open({ placement = "sidebar" })
+        local sidebar_buf, sidebar_win = find_sidebar()
+        assert(sidebar_buf and sidebar_win)
+        local r = assert(require("git.core.repo").find(vim.fn.getcwd()))
+        r:refresh()
+        t.wait_for(function()
+            return r.status and #r.status:rows("unstaged") > 0
+        end, "git status to report unstaged changes")
+
+        local entry_line
+        for i, l in
+            ipairs(vim.api.nvim_buf_get_lines(sidebar_buf, 0, -1, false))
+        do
+            if l:match("file.txt$") then
+                entry_line = i
+                break
+            end
+        end
+        if not entry_line then
+            error("entry line should exist")
+        end
+
+        vim.api.nvim_set_current_win(sidebar_win)
+        vim.api.nvim_win_set_cursor(sidebar_win, { entry_line, 0 })
+        t.press("<Tab>")
+        t.wait_for(function()
+            return find_diff_win("left") ~= nil
+                and find_diff_win("right") ~= nil
+        end, "diff pair to appear")
+
+        local left_win = assert(find_diff_win("left"))
+        local right_win = assert(find_diff_win("right"))
+        local left_top =
+            vim.api.nvim_win_call(left_win, function() return vim.fn.line("w0") end)
+        local right_top = vim.api.nvim_win_call(
+            right_win,
+            function() return vim.fn.line("w0") end
+        )
+        t.eq(
+            left_top,
+            right_top,
+            "left and right panes should have the same topline after diffsplit"
+        )
+        t.eq(
+            vim.api.nvim_win_get_cursor(left_win),
+            { 1, 0 },
+            "left pane should start at line 1"
+        )
+        t.eq(
+            vim.api.nvim_win_get_cursor(right_win),
+            { 1, 0 },
+            "right pane should start at line 1"
+        )
+    end
+)