Add commit log to brief diff output

Shows oneline commit summaries between the compared refs. The git log
runs concurrently with the detection engine to avoid adding latency.

Author: andrew

brief.go

@@ -161,6 +161,7 @@ type Report struct {
 	Version         string                 `json:"version"`
 	Path            string                 `json:"path"`
 	DiffRef         string                 `json:"diff_ref,omitempty"`
+	DiffCommits     []string               `json:"diff_commits,omitempty"`
 	ChangedFiles    []string               `json:"changed_files,omitempty"`
 	Languages       []Detection            `json:"languages"`
 	PackageManagers []Detection            `json:"package_managers"`

cmd/brief/diff.go

@@ -74,14 +74,24 @@ func cmdDiff(args []string) {
 		os.Exit(1)
 	}
 
+	// Run detection and git log concurrently.
+	var commits []string
+	done := make(chan struct{})
+	go func() {
+		commits = gitCommitLog(root, ref1, ref2)
+		close(done)
+	}()
+
 	engine := detect.New(knowledgeBase, root)
 	r, err := engine.Run()
 	if err != nil {
 		_, _ = fmt.Fprintf(os.Stderr, "error: %v\n", err)
 		os.Exit(1)
 	}
 
+	<-done
 	r.DiffRef = diffRef
+	r.DiffCommits = commits
 	r.ChangedFiles = changedFiles
 
 	r = detect.FilterByChangedFiles(r, knowledgeBase, changedFiles)
@@ -142,7 +152,7 @@ func gitChangedFiles(ctx context.Context, root, ref1, ref2 string, includeUncomm
 	var files []string
 
 	addFiles := func(output string) {
-		for _, f := range strings.Split(strings.TrimSpace(output), "\n") {
+		for f := range strings.SplitSeq(strings.TrimSpace(output), "\n") {
 			f = strings.TrimSpace(f)
 			if f != "" && !seen[f] {
 				seen[f] = true
@@ -216,3 +226,28 @@ func gitChangedFiles(ctx context.Context, root, ref1, ref2 string, includeUncomm
 
 	return files, nil
 }
+
+// gitCommitLog returns oneline commit summaries between two refs.
+func gitCommitLog(root, ref1, ref2 string) []string {
+	var args []string
+	if ref2 != "" {
+		args = []string{"log", "--oneline", ref1 + ".." + ref2}
+	} else {
+		args = []string{"log", "--oneline", ref1 + "..HEAD"}
+	}
+
+	cmd := exec.Command("git", args...)
+	cmd.Dir = root
+	out, err := cmd.Output()
+	if err != nil {
+		return nil
+	}
+
+	var commits []string
+	for line := range strings.SplitSeq(strings.TrimSpace(string(out)), "\n") {
+		if line != "" {
+			commits = append(commits, line)
+		}
+	}
+	return commits
+}

detect/filter.go

@@ -40,6 +40,7 @@ func FilterByChangedFiles(r *brief.Report, knowledgeBase *kb.KnowledgeBase, chan
 		Version:      r.Version,
 		Path:         r.Path,
 		DiffRef:      r.DiffRef,
+		DiffCommits:  r.DiffCommits,
 		ChangedFiles: r.ChangedFiles,
 		Tools:        make(map[string][]brief.Detection),
 		Git:          r.Git,

report/report.go

@@ -42,6 +42,19 @@ func Human(w io.Writer, r *brief.Report, verbose bool) {
 
 	_, _ = fmt.Fprintln(w)
 
+	// Commits (in diff mode only)
+	if len(r.DiffCommits) > 0 {
+		_, _ = fmt.Fprintf(w, "Commits:\n")
+		limit := min(len(r.DiffCommits), 20)
+		for _, c := range r.DiffCommits[:limit] {
+			_, _ = fmt.Fprintf(w, "  %s\n", sanitize(c))
+		}
+		if len(r.DiffCommits) > 20 {
+			_, _ = fmt.Fprintf(w, "  ... and %d more\n", len(r.DiffCommits)-20)
+		}
+		_, _ = fmt.Fprintln(w)
+	}
+
 	// Changed files (in diff mode only)
 	if len(r.ChangedFiles) > 0 {
 		_, _ = fmt.Fprintf(w, "Changed:\n")