refactor(git): rewrite diff module around :diffsplit

lua/git/diff.lua

@@ -1,175 +1,134 @@
 local Revision = require("git.core.revision")
+local object = require("git.object")
 local repo = require("git.core.repo")
 local util = require("git.core.util")
 
 local M = {}
 
----@class ow.Git.Diff.Side
----@field buf integer
----@field name string?
-
----@class ow.Git.Diff.Pair
----@field left ow.Git.Diff.Side
----@field right ow.Git.Diff.Side
-
----@param win integer
----@param enabled boolean
-function M.set_diff(win, enabled)
-    vim.api.nvim_win_call(win, function()
-        vim.cmd(enabled and "diffthis" or "diffoff")
-    end)
-end
-
----@param left integer
----@param right integer
----@param vertical boolean
-function M.open(left, right, vertical)
-    vim.cmd.normal({ "m'", bang = true })
-    vim.api.nvim_set_current_buf(right)
-    vim.cmd.diffthis()
-    vim.api.nvim_open_win(left, true, {
-        split = vertical and "left" or "above",
-    })
-    vim.cmd.diffthis()
-end
-
----@param left_win integer
----@param right_win integer
----@param pair ow.Git.Diff.Pair
-function M.update_pair(left_win, right_win, pair)
-    M.set_diff(left_win, false)
-    M.set_diff(right_win, false)
-    vim.api.nvim_win_set_buf(left_win, pair.left.buf)
-    vim.api.nvim_win_set_buf(right_win, pair.right.buf)
-    for _, side in ipairs({ pair.left, pair.right }) do
-        if side.name then
-            util.set_buf_name(side.buf, side.name)
-        end
-    end
-    M.set_diff(left_win, true)
-    M.set_diff(right_win, true)
-    vim.api.nvim_win_set_cursor(left_win, { 1, 0 })
-    vim.api.nvim_win_set_cursor(right_win, { 1, 0 })
-    vim.cmd.syncbind()
-end
-
----@param buf_a integer
----@param buf_b integer
----@param a_left boolean
----@param vertical boolean
-local function place_pair(buf_a, buf_b, a_left, vertical)
-    if a_left then
-        M.open(buf_a, buf_b, vertical)
-    else
-        M.open(buf_b, buf_a, vertical)
-    end
-end
-
----@param opts ow.Git.Diff.SplitOpts
----@param buf integer
----@param rev ow.Git.Revision
-local function uri_split(opts, buf, rev)
-    local r = repo.resolve(buf)
-    if not r then
-        util.error("git URI buffer has no worktree")
-        return
-    end
-    if not rev.path then
-        util.error("git URI has no path, cannot diff against worktree")
-        return
-    end
-    local object = require("git.object")
-
-    if opts.rev and opts.rev:find(":", 1, true) then
-        if not r:rev_parse(opts.rev, true) then
-            util.error("invalid rev: %s", opts.rev)
-            return
-        end
-        place_pair(
-            buf,
-            object.buf_for(r, Revision.parse(opts.rev)),
-            false,
-            opts.vertical
-        )
-        return
-    end
-
-    if not opts.rev then
-        local worktree_path = vim.fs.joinpath(r.worktree, rev.path)
-        if not vim.uv.fs_stat(worktree_path) then
-            util.error("worktree file does not exist: %s", rev.path)
-            return
-        end
-        local worktree_buf = vim.fn.bufadd(worktree_path)
-        vim.fn.bufload(worktree_buf)
-        place_pair(buf, worktree_buf, true, opts.vertical)
-        return
-    end
-
-    if rev.stage == 1 then
-        util.warning("gD on merge base is ambiguous, use :Gdiffsplit <rev>")
-        return
-    end
-
-    local mapping = {
-        [2] = { Revision.new({ stage = 3, path = rev.path }), true },
-        [3] = { Revision.new({ stage = 2, path = rev.path }), false },
-        [0] = { Revision.new({ base = "HEAD", path = rev.path }), false },
-    }
-    local m = mapping[rev.stage]
-        or { Revision.new({ stage = 0, path = rev.path }), true }
-    local other_rev, left = m[1], m[2]
-    if not r:rev_parse(other_rev:format(), true) then
-        util.error("invalid rev: %s", other_rev:format())
-        return
-    end
-    place_pair(buf, object.buf_for(r, other_rev), left, opts.vertical)
-end
-
 ---@class ow.Git.Diff.SplitOpts
----@field rev string?
----@field vertical boolean
+---@field target string?
+---@field mods vim.api.keyset.cmd.mods?
 
----@param opts ow.Git.Diff.SplitOpts
-function M.split(opts)
-    local cur_buf = vim.api.nvim_get_current_buf()
-    local cur_path = vim.api.nvim_buf_get_name(cur_buf)
-
-    local cur_rev = require("git.object").parse_uri(cur_path)
+---@param cur_buf integer
+---@return string? target
+---@return string? err
+local function infer_target(cur_buf)
+    local cur_name = vim.api.nvim_buf_get_name(cur_buf)
+    local cur_rev = object.parse_uri(cur_name)
     if cur_rev then
-        return uri_split(opts, cur_buf, cur_rev)
+        local r = repo.resolve(cur_buf)
+        if not r then
+            return nil, "git URI buffer has no worktree"
+        end
+        if not cur_rev.path then
+            return nil, "git URI has no path, cannot diff against worktree"
+        end
+        local worktree_path = vim.fs.joinpath(r.worktree, cur_rev.path)
+        if not vim.uv.fs_stat(worktree_path) then
+            return nil, "worktree file does not exist: " .. cur_rev.path
+        end
+        return worktree_path, nil
     end
 
-    if cur_path == "" then
-        util.error("no file in current buffer")
-        return
+    if cur_name == "" then
+        return nil, "no file in current buffer"
     end
     if vim.bo[cur_buf].buftype ~= "" then
-        util.error("cannot diff this buffer (not a worktree file)")
-        return
+        return nil, "cannot diff this buffer (not a worktree file)"
     end
-    cur_path = vim.fn.resolve(cur_path)
-    local r = repo.resolve(cur_path)
+    local resolved = vim.fn.resolve(cur_name)
+    local r = repo.resolve(resolved)
     if not r then
-        util.error("not in a git repository")
-        return
+        return nil, "not in a git repository"
     end
-    local rel = vim.fs.relpath(r.worktree, cur_path)
+    local rel = vim.fs.relpath(r.worktree, resolved)
+    if not rel then
+        return nil, "current buffer is outside the worktree"
+    end
+    return object.format_uri(Revision.new({ stage = 0, path = rel })), nil
+end
 
-    local rev
-    if not opts.rev then
-        rev = Revision.new({ stage = 0, path = rel })
-    elseif opts.rev:find(":", 1, true) then
-        rev = Revision.parse(opts.rev)
-    else
-        rev = Revision.new({ base = opts.rev, path = rel })
+---@param target string
+---@param cur_buf integer
+---@return string? resolved
+---@return string? err
+local function resolve_target(target, cur_buf)
+    if vim.startswith(target, object.URI_PREFIX) then
+        return target, nil
     end
-    if not r:rev_parse(rev:format(), true) then
-        util.error("invalid rev: %s", rev:format())
+    if vim.fn.filereadable(target) == 1 then
+        return target, nil
+    end
+    local cur_name = vim.api.nvim_buf_get_name(cur_buf)
+    local cur_rev = object.parse_uri(cur_name)
+    local r, rel
+    if cur_rev and cur_rev.path then
+        r = repo.resolve(cur_buf)
+        rel = cur_rev.path
+    elseif cur_name ~= "" then
+        local resolved = vim.fn.resolve(cur_name)
+        r = repo.resolve(resolved)
+        if r then
+            rel = vim.fs.relpath(r.worktree, resolved)
+        end
+    end
+    if not r then
+        return nil, "not in a git repository"
+    end
+    if not rel then
+        return nil, "current buffer has no path"
+    end
+    if not r:rev_parse(target, true) then
+        return nil, "invalid rev: " .. target
+    end
+    return object.format_uri(Revision.new({ base = target, path = rel })), nil
+end
+
+---@param cur_buf integer
+---@param target string
+---@return 'aboveleft'|'belowright'|nil
+local function default_split(cur_buf, target)
+    local cur_rev = object.parse_uri(vim.api.nvim_buf_get_name(cur_buf))
+    local target_rev = object.parse_uri(target)
+    if not cur_rev and target_rev then
+        return "aboveleft"
+    end
+    if cur_rev and not target_rev then
+        return "belowright"
+    end
+    if cur_rev and target_rev then
+        if cur_rev.stage == 0 and target_rev.base then
+            return "aboveleft"
+        end
+        if cur_rev.base and target_rev.stage == 0 then
+            return "belowright"
+        end
+    end
+    return nil
+end
+
+---@param opts? ow.Git.Diff.SplitOpts
+function M.split(opts)
+    opts = opts or {}
+    local cur_buf = vim.api.nvim_get_current_buf()
+    local target, err
+    if opts.target then
+        target, err = resolve_target(opts.target, cur_buf)
+    else
+        target, err = infer_target(cur_buf)
+    end
+    if not target then
+        util.error("%s", err or "no diff target")
         return
     end
-    local buf = require("git.object").buf_for(r, rev)
-    place_pair(buf, cur_buf, true, opts.vertical)
+    local mods = opts.mods
+    if not mods or mods.split == nil then
+        local placement = default_split(cur_buf, target)
+        if placement then
+            mods = vim.tbl_extend("force", mods or {}, { split = placement })
+        end
+    end
+    vim.cmd.diffsplit({ args = { target }, mods = mods })
 end
 
 return M

lua/git/object.lua

@@ -334,7 +334,12 @@ local function open_section(r, section)
     local left = side_buf(r, section.blob_a, section.path_a)
     local right = side_buf(r, section.blob_b, section.path_b)
     if left and right then
-        require("git.diff").open(left, right, true)
+        vim.cmd.normal({ "m'", bang = true })
+        vim.api.nvim_set_current_buf(right)
+        require("git.diff").split({
+            target = vim.api.nvim_buf_get_name(left),
+            mods = { vertical = true },
+        })
         return
     end
     if not left and not right then

lua/git/status_view.lua

@@ -176,9 +176,13 @@ local function current_entry(bufnr)
     return s, s.lines[lnum]
 end
 
+---@class ow.Git.StatusView.Pane
+---@field buf integer
+---@field name string?
+
 ---@param r ow.Git.Repo
 ---@param path string
----@return ow.Git.Diff.Side
+---@return ow.Git.StatusView.Pane
 local function head_pane(r, path)
     local rev = Revision.new({ base = "HEAD", path = path })
     return {
@@ -189,7 +193,7 @@ end
 
 ---@param r ow.Git.Repo
 ---@param path string
----@return ow.Git.Diff.Side
+---@return ow.Git.StatusView.Pane
 local function worktree_pane(r, path)
     local buf = vim.fn.bufadd(vim.fs.joinpath(r.worktree, path))
     vim.fn.bufload(buf)
@@ -198,7 +202,7 @@ end
 
 ---@param s ow.Git.StatusView.State
 ---@param path string
----@return ow.Git.Diff.Side
+---@return ow.Git.StatusView.Pane
 local function index_pane(s, path)
     local rev = Revision.new({ stage = 0, path = path })
     return {
@@ -209,7 +213,7 @@ end
 
 ---@param s ow.Git.StatusView.State
 ---@param row ow.Git.Status.Row
----@return ow.Git.Diff.Side?
+---@return ow.Git.StatusView.Pane?
 local function older_pane(s, row)
     local entry = row.entry
     if row.section == "staged" then
@@ -227,7 +231,7 @@ end
 
 ---@param s ow.Git.StatusView.State
 ---@param row ow.Git.Status.Row
----@return ow.Git.Diff.Side?
+---@return ow.Git.StatusView.Pane?
 local function newer_pane(s, row)
     local entry = row.entry
     if row.section == "staged" then
@@ -250,15 +254,6 @@ local function newer_pane(s, row)
     return nil
 end
 
----@param win integer
-local function reset_diff_win(win)
-    vim.api.nvim_win_call(win, function()
-        vim.cmd(
-            "setlocal winfixwidth< number< relativenumber< signcolumn< wrap< cursorline<"
-        )
-    end)
-end
-
 ---@param target_win integer
 ---@param dir "left"|"right"
 ---@return integer
@@ -268,6 +263,9 @@ local function vsplit_at(target_win, dir)
         true,
         { split = dir, win = target_win }
     )
+    vim.api.nvim_win_call(win, function()
+        vim.cmd("setlocal winfixwidth<")
+    end)
     vim.cmd.clearjumps()
     return win
 end
@@ -322,8 +320,7 @@ local function view_row(s, row, focus_left)
 
     if s.placement ~= "sidebar" then
         local pane = right or left
-        ---@cast pane ow.Git.Diff.Side
-        diff.set_diff(status_win, false)
+        ---@cast pane -nil
         vim.cmd.normal({ "m'", bang = true })
         vim.api.nvim_win_set_buf(status_win, pane.buf)
         if pane.name then
@@ -338,12 +335,13 @@ local function view_row(s, row, focus_left)
     end
     close_other_diff_wins(status_win, target)
     vim.api.nvim_win_set_width(status_win, WINDOW_WIDTH)
-    reset_diff_win(target)
-    diff.set_diff(target, false)
+    vim.api.nvim_win_call(target, function()
+        vim.cmd.diffoff()
+    end)
 
     if not (left and right) then
         local side = right or left
-        ---@cast side ow.Git.Diff.Side
+        ---@cast side ow.Git.StatusView.Pane
         vim.api.nvim_win_set_buf(target, side.buf)
         if side.name then
             util.set_buf_name(side.buf, side.name)
@@ -351,16 +349,23 @@ local function view_row(s, row, focus_left)
         vim.api.nvim_set_current_win(focus_left and target or status_win)
         return
     end
-    ---@cast left ow.Git.Diff.Side
-    ---@cast right ow.Git.Diff.Side
+    ---@cast left ow.Git.StatusView.Pane
+    ---@cast right ow.Git.StatusView.Pane
 
-    local left_win = vsplit_at(target, "left")
-    reset_diff_win(left_win)
-    local combined = vim.api.nvim_win_get_width(left_win)
-        + vim.api.nvim_win_get_width(target)
-    vim.api.nvim_win_set_width(left_win, math.floor(combined / 2))
+    vim.api.nvim_win_set_buf(target, right.buf)
+    if right.name then
+        util.set_buf_name(right.buf, right.name)
+    end
 
-    diff.update_pair(left_win, target, { left = left, right = right })
+    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({
+            target = older,
+            mods = { vertical = true },
+        })
+        left_win = vim.api.nvim_get_current_win()
+    end)
     vim.api.nvim_set_current_win(focus_left and left_win or status_win)
 end
 

plugin/git.lua

@@ -142,22 +142,18 @@ end
 
 local DIFF_DIRECTIONS = { "vertical", "horizontal" }
 
-local function default_vertical()
-    return vim.tbl_contains(vim.opt.diffopt:get(), "vertical")
-end
-
 vim.api.nvim_create_user_command("Gdiffsplit", function(opts)
     local fargs = opts.fargs
-    local vertical = default_vertical()
+    local mods = nil
     local rev_idx = 1
     if fargs[1] == "vertical" then
-        vertical = true
+        mods = { vertical = true }
         rev_idx = 2
     elseif fargs[1] == "horizontal" then
-        vertical = false
+        mods = { vertical = false }
         rev_idx = 2
     end
-    require("git.diff").split({ rev = fargs[rev_idx], vertical = vertical })
+    require("git.diff").split({ target = fargs[rev_idx], mods = mods })
 end, {
     nargs = "*",
     complete = function(arg_lead, cmd_line, _)
@@ -219,16 +215,22 @@ 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()
-    require("git.diff").split({ vertical = true })
+    require("git.diff").split({ mods = { vertical = true } })
 end, { silent = true, desc = "Diff against index (vertical)" })
 vim.keymap.set("n", "<Plug>(git-diff-horizontal)", function()
-    require("git.diff").split({ vertical = false })
+    require("git.diff").split({ mods = { vertical = false } })
 end, { silent = true, desc = "Diff against index (horizontal)" })
 vim.keymap.set("n", "<Plug>(git-diff-vertical-head)", function()
-    require("git.diff").split({ rev = "HEAD", vertical = true })
+    require("git.diff").split({
+        target = "HEAD",
+        mods = { vertical = true },
+    })
 end, { silent = true, desc = "Diff against HEAD (vertical)" })
 vim.keymap.set("n", "<Plug>(git-diff-horizontal-head)", function()
-    require("git.diff").split({ rev = "HEAD", vertical = false })
+    require("git.diff").split({
+        target = "HEAD",
+        mods = { vertical = false },
+    })
 end, { silent = true, desc = "Diff against HEAD (horizontal)" })
 
 vim.keymap.set("n", "<Plug>(git-status-toggle)", function()

test/git/status_view_test.lua

@@ -234,3 +234,84 @@ t.test("refresh on stage updates the index URI buffer's content", function()
         "index pane should reflect staged content after refresh"
     )
 end)
+
+t.test(
+    "re-selecting same entry after close + diffsplit keeps fold state in sync",
+    function()
+        local committed, worktree = {}, {}
+        for i = 1, 30 do
+            committed[i] = "line " .. i
+            worktree[i] = i == 15 and "CHANGED" or ("line " .. i)
+        end
+        local sidebar_win, line = setup_sidebar_with_unstaged_file(
+            "foo.txt",
+            table.concat(committed, "\n") .. "\n",
+            table.concat(worktree, "\n") .. "\n"
+        )
+
+        local prev_foldlevel = vim.o.foldlevel
+        vim.o.foldlevel = 99
+        t.defer(function()
+            vim.o.foldlevel = prev_foldlevel
+        end)
+
+        vim.api.nvim_set_current_win(sidebar_win)
+        vim.api.nvim_win_set_cursor(sidebar_win, { line, 0 })
+        t.press("<Tab>")
+        t.wait_for(function()
+            return find_diff_win("left") ~= nil
+                and find_diff_win("right") ~= nil
+        end, "first diff pair to appear")
+
+        local first_left = assert(find_diff_win("left"))
+        vim.api.nvim_win_close(first_left, false)
+
+        local remaining
+        for _, w in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
+            if w ~= sidebar_win then
+                remaining = w
+                break
+            end
+        end
+        if not remaining then
+            error("a non-sidebar window should remain after close")
+        end
+        vim.api.nvim_set_current_win(remaining)
+        require("git.diff").split({ mods = { vertical = true } })
+        t.wait_for(function()
+            local count = 0
+            for _, w in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
+                if vim.wo[w].diff then
+                    count = count + 1
+                end
+            end
+            return count == 2
+        end, "diffsplit to produce a diff pair")
+
+        vim.api.nvim_set_current_win(sidebar_win)
+        vim.api.nvim_win_set_cursor(sidebar_win, { line, 0 })
+        t.press("<Tab>")
+        t.wait_for(function()
+            local count = 0
+            for _, w in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
+                if vim.wo[w].diff then
+                    count = count + 1
+                end
+            end
+            return count == 2
+        end, "diff pair after re-selecting entry")
+
+        local left_win = assert(find_diff_win("left"))
+        local right_win = assert(find_diff_win("right"))
+        t.eq(
+            vim.wo[left_win].foldlevel,
+            0,
+            "left pane foldlevel should be 0 after re-select"
+        )
+        t.eq(
+            vim.wo[right_win].foldlevel,
+            0,
+            "right pane foldlevel should be 0 after re-select"
+        )
+    end
+)