perf(git): fold revspec validation into the cat-file -p the loader needs anyway

lua/git/diff.lua

@@ -157,13 +157,17 @@ local function uri_split(opts, cur_buf, cur_revspec)
     local cur_writable = cur.stage == 0
 
     if opts.revspec ~= "" and opts.revspec:find(":", 1, true) then
-        if not repo.object_exists(worktree, opts.revspec) then
+        local content = util.exec(
+            { "git", "cat-file", "-p", opts.revspec },
+            { cwd = worktree, silent = true }
+        )
+        if not content then
             util.warning("invalid revspec: %s", opts.revspec)
             return
         end
         place_pair(
             cur_buf,
-            object.buf_for(worktree, opts.revspec),
+            object.buf_for(worktree, opts.revspec, content),
             cur_writable,
             opts.vertical
         )
@@ -192,13 +196,17 @@ local function uri_split(opts, cur_buf, cur_revspec)
     else
         other_revspec = ":0:" .. cur.path
     end
-    if not repo.object_exists(worktree, other_revspec) then
+    local content = util.exec(
+        { "git", "cat-file", "-p", other_revspec },
+        { cwd = worktree, silent = true }
+    )
+    if not content then
         util.warning("invalid revspec: %s", other_revspec)
         return
     end
     place_pair(
         cur_buf,
-        object.buf_for(worktree, other_revspec),
+        object.buf_for(worktree, other_revspec, content),
         cur.stage ~= nil,
         opts.vertical
     )
@@ -248,13 +256,16 @@ function M.split(opts)
     else
         revspec = opts.revspec .. ":" .. rel
     end
-    if not repo.object_exists(worktree, revspec) then
+    local content = util.exec(
+        { "git", "cat-file", "-p", revspec },
+        { cwd = worktree, silent = true }
+    )
+    if not content then
         util.warning("invalid revspec: %s", revspec)
         return
     end
-    local buf = vim.fn.bufadd("git://" .. revspec)
-    vim.b[buf].git_worktree = worktree
-
+    local object = require("git.object")
+    local buf = object.buf_for(worktree, revspec, content)
     local other_writable = util.parse_revspec(revspec).stage == 0
     place_pair(buf, cur_buf, other_writable, opts.vertical)
 end

lua/git/object.lua

@@ -135,16 +135,29 @@ local function attach_index_writer(buf, worktree, path)
     })
 end
 
+---Pre-fetched content keyed by bufnr. Set by `buf_for(_, _, content)`
+---and consumed by the next `read_uri` dispatch on that buffer. Lets
+---callers fold validation + content fetch + buffer load into one
+---`cat-file` call instead of preflighting separately.
+---@type table<integer, string>
+local pending_content = {}
+
 ---Return a buffer holding the content addressed by a git revspec. The
 ---URI is `git://<revspec>` and BufReadCmd routes through `M.read_uri`,
----which loads via `git cat-file -p`.
+---which loads via `git cat-file -p`. If `content` is given, primes a
+---cache so the BufReadCmd handler reuses it instead of running another
+---`cat-file -p`.
 ---@param worktree string
 ---@param revspec string  any revspec git understands (e.g. `HEAD:foo`, `:foo`, `:1:foo`, `<sha>`, `<sha>:foo`)
+---@param content string?
 ---@return integer
-function M.buf_for(worktree, revspec)
+function M.buf_for(worktree, revspec, content)
     local name = "git://" .. revspec
     local buf = vim.fn.bufadd(name)
     vim.b[buf].git_worktree = worktree
+    if content then
+        pending_content[buf] = content
+    end
     vim.fn.bufload(buf)
     return buf
 end
@@ -172,10 +185,14 @@ function M.read_uri(buf)
     vim.bo[buf].swapfile = false
     vim.bo[buf].bufhidden = "wipe"
 
-    local stdout = util.exec(
+    local stdout = pending_content[buf]
+    pending_content[buf] = nil
+    if stdout == nil then
+        stdout = util.exec(
             { "git", "cat-file", "-p", revspec },
             { cwd = worktree }
         )
+    end
     if stdout then
         vim.api.nvim_buf_set_lines(buf, 0, -1, false, util.split_lines(stdout))
     end

lua/git/repo.lua

@@ -343,18 +343,4 @@ function M.rev_parse(worktree, ref, short)
     return trimmed ~= "" and trimmed or nil
 end
 
----Verify a revspec resolves to an existing git object. `cat-file -e` is
----git's cheapest existence check, and unlike `rev-parse --verify` it
----also accepts the `<commit>:<path>` form that BufReadCmd revspec URIs
----use.
----@param worktree string
----@param revspec string
----@return boolean
-function M.object_exists(worktree, revspec)
-    return util.exec(
-        { "git", "cat-file", "-e", revspec },
-        { cwd = worktree, silent = true }
-    ) ~= nil
-end
-
 return M