feat(git): trim hunk preview header, focus float on re-invoke

lua/git/hunks.lua

@@ -446,12 +446,9 @@ function M.nav(direction)
 end
 
 ---@param h ow.Git.Hunks.Hunk
----@param state ow.Git.Hunks.BufState
+---@return string[]
----@return string
+local function hunk_body(h)
-local function build_patch(h, state)
     local lines = {
-        "--- a/" .. state.rel,
-        "+++ b/" .. state.rel,
         string.format(
             "@@ -%d,%d +%d,%d @@",
             h.old_start,
@@ -466,6 +463,15 @@ local function build_patch(h, state)
     for _, l in ipairs(h.new_lines) do
         table.insert(lines, "+" .. l)
     end
+    return lines
+end
+
+---@param h ow.Git.Hunks.Hunk
+---@param state ow.Git.Hunks.BufState
+---@return string
+local function build_patch(h, state)
+    local lines = { "--- a/" .. state.rel, "+++ b/" .. state.rel }
+    vim.list_extend(lines, hunk_body(h))
     return table.concat(lines, "\n") .. "\n"
 end
 
@@ -543,16 +549,22 @@ function M.select_hunk(buf)
     vim.api.nvim_win_set_cursor(0, { last, 0 })
 end
 
+local preview_win ---@type integer?
+
 ---@param buf? integer
 function M.preview_hunk(buf)
-    local _, state, h = cursor_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 = util.split_lines(build_patch(h, state))
+    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"
@@ -573,19 +585,33 @@ function M.preview_hunk(buf)
         height = height,
         style = "minimal",
     })
-    vim.api.nvim_create_autocmd({ "CursorMoved", "InsertEnter", "BufLeave" }, {
+    preview_win = win
-        once = true,
+
-        callback = function()
+    local function close()
-            if vim.api.nvim_win_is_valid(win) then
-                vim.api.nvim_win_close(win, true)
-            end
-        end,
-    })
-    vim.keymap.set("n", "q", function()
         if vim.api.nvim_win_is_valid(win) then
             vim.api.nvim_win_close(win, true)
         end
-    end, { buffer = pbuf, nowait = true })
+    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)

test/git/hunks_test.lua

@@ -52,6 +52,15 @@ local function detailed_marks(buf, 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")
@@ -296,6 +305,52 @@ t.test("git_hunk_signs falls back to the default for unset kinds", function()
     })
 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)