feat(git): route commit through GIT_EDITOR proxy

lua/git/commit.lua

@@ -1,3 +1,5 @@
+local editor = require("git.editor")
+local git = require("git")
 local log = require("log")
 local repo = require("git.repo")
 
@@ -6,89 +8,70 @@ local M = {}
 ---@param opts { amend: boolean? }?
 function M.commit(opts)
     local amend = opts and opts.amend or false
-    local gitdir, worktree = repo.resolve_cwd()
-    if not gitdir or not worktree then
+    local _, worktree = repo.resolve_cwd()
+    if not worktree then
         log.warning("not in a git repository")
         return
     end
-    local msg_path = vim.fs.joinpath(gitdir, "COMMIT_EDITMSG")
 
-    local initial = ""
+    local cmd = { "git", "commit" }
     if amend then
-        local result = vim.system(
-            { "git", "log", "-1", "--pretty=%B" },
-            { cwd = worktree, text = true }
-        ):wait()
-        if result.code == 0 then
-            initial = (result.stdout or ""):gsub("\n+$", "")
-        else
-            log.warning("git log -1 failed: %s", vim.trim(result.stderr or ""))
+        table.insert(cmd, "--amend")
+    end
+
+    local proxy_buf
+    editor.run(cmd, { cwd = worktree }, function(file_path, done)
+        local lines = {}
+        local f = io.open(file_path, "r")
+        if f then
+            for line in f:lines() do
+                table.insert(lines, line)
+            end
+            f:close()
         end
-    end
 
-    local f, err = io.open(msg_path, "w")
-    if not f then
-        log.error("failed to open %s: %s", msg_path, err or "")
-        return
-    end
-    f:write(initial)
-    f:close()
+        local buf = git.new_scratch({ name = file_path })
+        proxy_buf = buf
+        vim.bo[buf].buftype = "acwrite"
+        vim.bo[buf].bufhidden = "wipe"
+        vim.bo[buf].modifiable = true
+        vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
+        vim.bo[buf].modified = false
+        vim.bo[buf].filetype = "gitcommit"
 
-    local ok, err = pcall(vim.cmd.edit, vim.fn.fnameescape(msg_path))
-    if not ok then
-        log.error("failed to open %s: %s", msg_path, err or "")
-        return
-    end
-    local buf = vim.api.nvim_get_current_buf()
-    if vim.api.nvim_buf_get_name(buf) ~= msg_path then
-        -- `:edit` returned without surfacing an error but didn't actually
-        -- switch (defensive against an unusual ftplugin/autocmd path). Bail
-        -- before attaching a BufWriteCmd that would overwrite the wrong
-        -- file on the next `:w`.
-        log.error("failed to switch to %s", msg_path)
-        return
-    end
-    vim.bo[buf].filetype = "gitcommit"
+        vim.api.nvim_create_autocmd("BufWriteCmd", {
+            buffer = buf,
+            callback = function()
+                local out = vim.api.nvim_buf_get_lines(buf, 0, -1, false)
+                local fw, werr = io.open(file_path, "w")
+                if not fw then
+                    log.error("failed to write %s: %s", file_path, werr or "")
+                    return
+                end
+                fw:write(table.concat(out, "\n"))
+                fw:close()
+                vim.bo[buf].modified = false
+            end,
+        })
 
-    vim.api.nvim_create_autocmd("BufWriteCmd", {
-        buffer = buf,
-        callback = function()
-            local lines = vim.api.nvim_buf_get_lines(buf, 0, -1, false)
-            local fw, werr = io.open(msg_path, "w")
-            if not fw then
-                log.error("failed to write %s: %s", msg_path, werr or "")
-                return
-            end
-            fw:write(table.concat(lines, "\n"))
-            fw:close()
-            vim.bo[buf].modified = false
-
-            local cmd = { "git", "commit", "-F", msg_path }
-            if amend then
-                table.insert(cmd, "--amend")
-            end
-            vim.system(
-                cmd,
-                { cwd = worktree, text = true },
-                vim.schedule_wrap(function(result)
-                    if result.code ~= 0 then
-                        log.error(
-                            "git commit failed: %s",
-                            vim.trim(result.stderr or "")
-                        )
-                        return
-                    end
-                    local out = vim.trim(result.stdout or "")
-                    if out ~= "" then
-                        log.info("%s", out)
-                    end
-                    if vim.api.nvim_buf_is_valid(buf) then
-                        vim.api.nvim_buf_delete(buf, { force = true })
-                    end
-                end)
-            )
-        end,
-    })
+        vim.api.nvim_create_autocmd("BufWipeout", {
+            buffer = buf,
+            once = true,
+            callback = done,
+        })
+    end, function(result)
+        if proxy_buf and vim.api.nvim_buf_is_valid(proxy_buf) then
+            vim.api.nvim_buf_delete(proxy_buf, { force = true })
+        end
+        if result.code ~= 0 then
+            log.error("git commit failed: %s", vim.trim(result.stderr or ""))
+            return
+        end
+        local out = vim.trim(result.stdout or "")
+        if out ~= "" then
+            log.info("%s", out)
+        end
+    end)
 end
 
 return M

lua/git/editor.lua

@@ -0,0 +1,141 @@
+local log = require("log")
+
+local M = {}
+
+local SENTINEL = "__NVIM_GIT_EDIT__"
+
+-- Each git editor invocation runs this body afresh under `sh -c`. The
+-- body picks a per-invocation flag file via `$$` (the wrapping shell's
+-- pid), prints the sentinel + flag-path + abs-path on stderr so the
+-- running Neovim can find both, and polls the flag until Neovim writes
+-- it. Concurrent edits inside one git call (e.g. `rebase -i`'s todo
+-- plus N reword commits) get distinct flags because each invocation is
+-- a fresh shell with a fresh `$$`.
+local SCRIPT = string.format(
+    [=[set -eu
+flag="${TMPDIR:-/tmp}/nvim-git-editor-$$.done"
+trap 'rm -f "$flag"' EXIT
+abs=$(realpath "$1")
+printf '%s\t%%s\t%%s\n' "$flag" "$abs" >&2
+while [ ! -e "$flag" ]; do
+    sleep 0.05
+done
+]=],
+    SENTINEL
+)
+
+---POSIX shell single-quote escape: foo'bar -> 'foo'\''bar'.
+---@param s string
+---@return string
+local function shq(s)
+    return "'" .. s:gsub("'", "'\\''") .. "'"
+end
+
+local GIT_EDITOR = "sh -c " .. shq(SCRIPT) .. " --"
+
+---Build a stderr callback that strips our sentinel lines, accumulates
+---the rest, and dispatches `on_open(abs, done)` for each sentinel seen.
+---The `finalize(result)` helper drains any trailing partial line into
+---`result.stderr` so the caller can treat `result` like a plain
+---`vim.system` result.
+---@param on_open fun(file_path: string, done: fun())
+---@return fun(err: string?, data: string?), fun(result: vim.SystemCompleted)
+local function build_stderr_handler(on_open)
+    local pending = ""
+    local stderr_buf = {}
+
+    local function dispatch(flag_path, abs_path)
+        vim.schedule(function()
+            local fired = false
+            local function done()
+                if fired then
+                    return
+                end
+                fired = true
+                local fw = io.open(flag_path, "w")
+                if fw then
+                    fw:close()
+                end
+            end
+            local ok, err = pcall(on_open, abs_path, done)
+            if not ok then
+                log.error("git.editor on_open failed: %s", tostring(err))
+                done()
+            end
+        end)
+    end
+
+    local pattern = "^" .. SENTINEL .. "\t(.-)\t(.+)$"
+
+    local function on_stderr(_, data)
+        if not data or data == "" then
+            return
+        end
+        pending = pending .. data
+        while true do
+            local nl = pending:find("\n", 1, true)
+            if not nl then
+                break
+            end
+            local line = pending:sub(1, nl - 1)
+            pending = pending:sub(nl + 1)
+            local flag, abs = line:match(pattern)
+            if flag then
+                dispatch(flag, abs)
+            else
+                table.insert(stderr_buf, line)
+                table.insert(stderr_buf, "\n")
+            end
+        end
+    end
+
+    local function finalize(result)
+        if pending ~= "" then
+            table.insert(stderr_buf, pending)
+        end
+        result.stderr = table.concat(stderr_buf)
+    end
+
+    return on_stderr, finalize
+end
+
+---Run a git command with an editor proxy active. When git invokes the
+---editor, `on_open` fires with the absolute file path git wants edited
+---plus a `done` callback. The caller opens the file in a buffer and
+---invokes `done()` once the user is finished (typically from a
+---`BufWipeout` autocmd). For commands that fire the editor more than
+---once in a single git invocation (`git rebase -i`, with one call for
+---the todo and one per `reword`), `on_open` is invoked once per
+---editor handoff.
+---
+---`on_exit` is called on the main loop with a `vim.SystemCompleted`-
+---shaped result. `result.stderr` has our protocol sentinels stripped.
+---@param cmd string[]
+---@param opts? { cwd?: string, env?: table<string,string> }
+---@param on_open fun(file_path: string, done: fun())
+---@param on_exit fun(result: vim.SystemCompleted)
+function M.run(cmd, opts, on_open, on_exit)
+    opts = opts or {}
+    local on_stderr, finalize = build_stderr_handler(on_open)
+
+    local env = vim.tbl_extend("force", opts.env or {}, {
+        GIT_EDITOR = GIT_EDITOR,
+        GIT_SEQUENCE_EDITOR = GIT_EDITOR,
+    })
+
+    vim.system(
+        cmd,
+        {
+            cwd = opts.cwd,
+            text = true,
+            env = env,
+            stderr = on_stderr,
+        },
+        vim.schedule_wrap(function(result)
+            finalize(result)
+            on_exit(result)
+        end)
+    )
+end
+
+return M