From 8d3bdd083c3ec4f6992cee6a6bd9723f93279bd4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Steven=20Dee=20=28J=C5=8Dshin=29?= <git@wholezero.org>
Date: Sun, 18 May 2025 21:31:18 -0700
Subject: [PATCH] Better mtimes for github workflow build cache

Saves and restores mtimes to a file, also covering the `o/` directory to
hopefully preserve make dependency information better.
---
 .github/workflows/build.yml | 40 ++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 6bd20ffab..dbd94b3f5 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -27,22 +27,23 @@ jobs:
           # Full checkout needed for git-restore-mtime-bare.
           fetch-depth: 0
 
-      # TODO(jart): fork this action.
-      - uses: chetan/git-restore-mtime-action@v2
-
-      - uses: actions/cache@v4
+      - uses: actions/cache/restore@v4
+        id: cache
         with:
-          path: .cosmocc/${{ env.COSMOCC_VERSION }}
-          key: cosmocc-${{ env.COSMOCC_VERSION }}
-
-      - uses: actions/cache@v4
-        with:
-          path: o
-          key: o-${{ matrix.mode }}-${{ env.COSMOCC_VERSION }}-${{ github.sha }}
+          path: |
+            .cosmocc/${{ env.COSMOCC_VERSION }}
+            o
+          key: ${{ env.COSMOCC_VERSION }}-${{ matrix.mode }}-${{ github.sha }}
           restore-keys: |
-            o-${{ matrix.mode }}-${{ env.COSMOCC_VERSION }}-
-            o-${{ matrix.mode }}-
-            o-
+            ${{ env.COSMOCC_VERSION }}-${{ matrix.mode }}-
+            ${{ env.COSMOCC_VERSION }}-
+
+      - name: Restore mtimes
+        if: steps.cache.outputs.cache-hit == 'true'
+        run: |
+          while read mtime file; do
+            [ -f "$file" ] && touch -d "@$mtime" "$file"
+          done < o/.mtimes
 
       - name: support ape bins 1
         run: sudo cp -a build/bootstrap/ape.elf /usr/bin/ape
@@ -52,3 +53,14 @@ jobs:
 
       - name: make matrix
         run: V=0 make -j2 MODE=${{ matrix.mode }}
+
+      - name: Save mtimes
+        run: |
+          find o -type f -exec stat -c "%Y %n" {} \; > o/.mtimes
+
+      - uses: actions/cache/save@v4
+        with:
+          path: |
+            .cosmocc
+            o
+          key: ${{ env.COSMOCC_VERSION }}-${{ matrix.mode }}-${{ github.sha }}