From 2b363b904c3244a4d67f4db02cfa3d965100f079 Mon Sep 17 00:00:00 2001
From: Mike McQuaid <mike@mikemcquaid.com>
Date: Mon, 13 May 2024 23:53:44 +0100
Subject: [PATCH] brew.sh: cache HOMEBREW_VERSION on disk.
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This is a (relatively, for this Bash script) expensive operation that
can be trivially cached so: let's do so.

Speedup on my machine:

```
$ hyperfine "brew --version" "HOMEBREW_VERSION_CACHE=1 brew --version"
Benchmark 1: brew --version
  Time (mean ± σ):     173.4 ms ±   5.1 ms    [User: 28.7 ms, System: 67.0 ms]
  Range (min … max):   167.3 ms … 182.9 ms    15 runs

Benchmark 2: HOMEBREW_VERSION_CACHE=1 brew --version
  Time (mean ± σ):     145.9 ms ±   4.0 ms    [User: 22.4 ms, System: 33.9 ms]
  Range (min … max):   140.0 ms … 154.5 ms    17 runs

Summary
  HOMEBREW_VERSION_CACHE=1 brew --version ran
    1.19 ± 0.05 times faster than brew --version
```

Co-authored-by: Bo Anderson <mail@boanderson.me>
---
 Library/Homebrew/brew.sh | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index abe2ed6bf6..a3e2f76291 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -495,7 +495,27 @@ setup_git() {
 setup_curl
 setup_git
 
-HOMEBREW_VERSION="$("${HOMEBREW_GIT}" -C "${HOMEBREW_REPOSITORY}" describe --tags --dirty --abbrev=7 2>/dev/null)"
+GIT_DESCRIBE_CACHE="${HOMEBREW_REPOSITORY}/.git/describe-cache"
+GIT_REVISION=$("${HOMEBREW_GIT}" -C "${HOMEBREW_REPOSITORY}" rev-parse HEAD 2>/dev/null)
+if [[ -n "${GIT_REVISION}" ]]
+then
+  GIT_DESCRIBE_CACHE_FILE="${GIT_DESCRIBE_CACHE}/${GIT_REVISION}"
+  if [[ -f "${GIT_DESCRIBE_CACHE_FILE}" ]]
+  then
+    HOMEBREW_VERSION="$(cat "${GIT_DESCRIBE_CACHE_FILE}")"
+  else
+    rm -rf "${GIT_DESCRIBE_CACHE}"
+    HOMEBREW_VERSION="$("${HOMEBREW_GIT}" -C "${HOMEBREW_REPOSITORY}" describe --tags --dirty --abbrev=7 2>/dev/null)"
+    mkdir -p "${GIT_DESCRIBE_CACHE}"
+    echo "${HOMEBREW_VERSION}" >"${GIT_DESCRIBE_CACHE_FILE}"
+  fi
+  unset GIT_DESCRIBE_CACHE_FILE
+else
+  rm -rf "${GIT_DESCRIBE_CACHE}"
+fi
+unset GIT_REVISION
+unset GIT_DESCRIBE_CACHE
+
 HOMEBREW_USER_AGENT_VERSION="${HOMEBREW_VERSION}"
 if [[ -z "${HOMEBREW_VERSION}" ]]
 then