Cache Git Log

internal/pipeline/build.go

@@ -857,6 +857,11 @@ func collectGitAssetCreationTimes(p *project.Project) (map[string]time.Time, err
 	}
 	assetsRelPath = filepath.ToSlash(assetsRelPath)
 
+	cacheFile := filepath.Join(p.Root, ".git", "asset-creation-times.json")
+	if cache, err := loadCreationTimeCache(cacheFile, p.Root, assetsRelPath, p.Inventory.AssetFiles); err == nil {
+		return cache, nil
+	}
+
 	output, err := gitOutput(p.Root, "log", "--diff-filter=A", "--format=%ct", "--name-only", "--", assetsRelPath)
 	if err != nil {
 		return result, nil
@@ -892,9 +897,59 @@ func collectGitAssetCreationTimes(p *project.Project) (map[string]time.Time, err
 		}
 	}
 
+	_ = saveCreationTimeCache(cacheFile, p.Root, result)
 	return result, nil
 }
 
+type creationTimeCache struct {
+	Head  string           `json:"head"`
+	Times map[string]int64 `json:"times"`
+}
+
+func loadCreationTimeCache(cacheFile, root, assetsRel string, assetFiles []string) (map[string]time.Time, error) {
+	data, err := os.ReadFile(cacheFile)
+	if err != nil {
+		return nil, err
+	}
+	var cache creationTimeCache
+	if err := json.Unmarshal(data, &cache); err != nil {
+		return nil, err
+	}
+	currentHead, err := gitOutput(root, "rev-parse", "HEAD")
+	if err != nil {
+		return nil, err
+	}
+	currentHead = strings.TrimSpace(currentHead)
+	if cache.Head != currentHead {
+		return nil, fmt.Errorf("cache stale")
+	}
+	result := make(map[string]time.Time, len(cache.Times))
+	for k, v := range cache.Times {
+		result[k] = time.Unix(v, 0).UTC()
+	}
+	return result, nil
+}
+
+func saveCreationTimeCache(cacheFile, root string, times map[string]time.Time) error {
+	head, err := gitOutput(root, "rev-parse", "HEAD")
+	if err != nil {
+		return err
+	}
+	intTimes := make(map[string]int64, len(times))
+	for k, v := range times {
+		intTimes[k] = v.Unix()
+	}
+	cache := creationTimeCache{
+		Head:  strings.TrimSpace(head),
+		Times: intTimes,
+	}
+	data, err := json.Marshal(cache)
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(cacheFile, data, 0o644)
+}
+
 func gitOutput(dir string, args ...string) (string, error) {
 	cmd := exec.Command("git", args...)
 	if dir != "" {