From 40323d0e37d6c6950bb103503aac28cd68261637 Mon Sep 17 00:00:00 2001
From: Robby Russell <robby@planetargon.com>
Date: Sun, 6 Sep 2026 08:01:19 -0700
Subject: [PATCH] perf(init): read the OMZ revision from .git instead of
 forking git

`git rev-parse HEAD` was run on every startup only to stamp the
zcompdump metadata. Resolve HEAD by reading the git directory in zsh:
handles `.git` files (worktrees, submodules), worktree common dirs,
detached HEADs and packed refs, and falls back to `git rev-parse` when
anything looks unexpected.

Measured on macOS arm64, zsh 5.9: 7.4 ms -> 0.2 ms per interactive
start.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 oh-my-zsh.sh | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/oh-my-zsh.sh b/oh-my-zsh.sh
index b4e95e0ff..12da390c8 100644
--- a/oh-my-zsh.sh
+++ b/oh-my-zsh.sh
@@ -110,9 +110,51 @@ if [[ -z "$ZSH_COMPDUMP" ]]; then
   ZSH_COMPDUMP="${ZDOTDIR:-$HOME}/.zcompdump-${SHORT_HOST}-${ZSH_VERSION}"
 fi
 
+# Resolve the commit $ZSH is checked out at into $REPLY by reading the git
+# directory, so that no git process is forked on every startup.
+# Handles .git files (worktrees, submodules), worktree common dirs, detached
+# HEADs and packed refs. Returns 1 if anything is unexpected.
+_omz_git_head() {
+  local gitdir="$ZSH/.git" common head ref
+  local -a lines
+  REPLY=
+
+  # .git may be a file pointing at the real git dir
+  if [[ -f "$gitdir" ]]; then
+    read -r head 2>/dev/null < "$gitdir" || return 1
+    gitdir="${head#gitdir: }"
+    [[ "$gitdir" = /* ]] || gitdir="$ZSH/$gitdir"
+  fi
+
+  # worktrees keep their refs in the common git dir
+  common="$gitdir"
+  if [[ -f "$gitdir/commondir" ]]; then
+    read -r common 2>/dev/null < "$gitdir/commondir" || return 1
+    [[ "$common" = /* ]] || common="$gitdir/$common"
+  fi
+
+  [[ -r "$gitdir/HEAD" ]] || return 1
+  read -r head 2>/dev/null < "$gitdir/HEAD" || return 1
+
+  # detached HEAD: the file holds the commit itself
+  [[ "$head" = ref:\ * ]] || { REPLY="$head"; return 0 }
+
+  ref="${head#ref: }"
+  if [[ -r "$common/$ref" ]]; then
+    read -r REPLY 2>/dev/null < "$common/$ref" && return 0
+  fi
+
+  [[ -r "$common/packed-refs" ]] || return 1
+  lines=("${(@f)$(<"$common/packed-refs")}")
+  REPLY="${lines[(r)* $ref]%% *}"
+  [[ -n "$REPLY" ]]
+}
+
 # Construct zcompdump OMZ metadata
-zcompdump_revision="#omz revision: $(builtin cd -q "$ZSH"; git rev-parse HEAD 2>/dev/null)"
+_omz_git_head || REPLY="$(builtin cd -q "$ZSH"; git rev-parse HEAD 2>/dev/null)"
+zcompdump_revision="#omz revision: $REPLY"
 zcompdump_fpath="#omz fpath: $fpath"
+unset -f _omz_git_head
 
 # Delete the zcompdump file if OMZ zcompdump metadata changed
 if ! command grep -q -Fx "$zcompdump_revision" "$ZSH_COMPDUMP" 2>/dev/null \