From 418b730b793c50de4df5b9a4590df643a9150ee1 Mon Sep 17 00:00:00 2001
From: dan9186 <dan9186@gmail.com>
Date: Fri, 21 Nov 2025 11:38:28 -0800
Subject: [PATCH] add ability to match file extensions

---
 client/repos_diff.go | 36 ++++++++++++++++++++++++++++++++++++
 cmd/diff.go          |  7 +++++--
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/client/repos_diff.go b/client/repos_diff.go
index 935d5a1..26d5616 100644
--- a/client/repos_diff.go
+++ b/client/repos_diff.go
@@ -12,6 +12,7 @@ import (
 type DiffConfig struct {
 	IgnoreEmpty      bool
 	IgnoreFilePrefix []string
+	MatchExtension   []string
 	Args             []string
 }
 
@@ -37,6 +38,8 @@ func (c *Client) DiffRepos(ctx context.Context, dirs []string, cfg *DiffConfig)
 
 		err := cmd.Run()
 
+		out = matchExtensions(out, cfg.MatchExtension)
+
 		// filter first to have empty check accurate
 		out = filterLines(out, cfg.IgnoreFilePrefix)
 
@@ -84,3 +87,36 @@ func filterLines(buf *bytes.Buffer, prefixes []string) *bytes.Buffer {
 
 	return out
 }
+
+func matchExtensions(buf *bytes.Buffer, extensions []string) *bytes.Buffer {
+	if len(extensions) == 0 {
+		return buf
+	}
+
+	for i := range extensions {
+		if !strings.HasPrefix(extensions[i], ".") {
+			extensions[i] = "." + extensions[i]
+		}
+	}
+
+	scanner := bufio.NewScanner(buf)
+	out := &bytes.Buffer{}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		matched := false
+		for _, ext := range extensions {
+			if strings.HasSuffix(line, ext) {
+				matched = true
+				break
+			}
+		}
+
+		if matched {
+			out.WriteString(line + "\n")
+		}
+	}
+
+	return out
+}
diff --git a/cmd/diff.go b/cmd/diff.go
index 85384b5..0dd231c 100644
--- a/cmd/diff.go
+++ b/cmd/diff.go
@@ -13,6 +13,7 @@ var (
 	nameOnly         bool
 	ignoreEmtpy      bool
 	ignoreFilePrefix []string
+	matchExtension   []string
 )
 
 func init() {
@@ -20,9 +21,10 @@ func init() {
 
 	diffCmd.Flags().StringVar(&dir, "dir", ".", "directory to diff repos from")
 
-	diffCmd.Flags().BoolVar(&ignoreEmtpy, "ignore-empty", false, "ignore empty diffs")
-	diffCmd.Flags().StringArrayVar(&ignoreFilePrefix, "ignore-file-prefix", []string{}, "ignore files in diffs with the given prefix")
+	diffCmd.Flags().StringArrayVar(&ignoreFilePrefix, "ignore-file-prefix", []string{}, "ignore files in diffs with the given prefix(es)")
+	diffCmd.Flags().StringArrayVar(&matchExtension, "match-extension", []string{}, "only include files in diffs with the given extension(s)")
 
+	diffCmd.Flags().BoolVar(&ignoreEmtpy, "ignore-empty", false, "ignore empty diffs")
 	diffCmd.Flags().BoolVar(&short, "shortstat", false, "show only the number of changed files, insertions, and deletions")
 	diffCmd.Flags().BoolVar(&nameOnly, "name-only", false, "show only names of changed files")
 
@@ -59,6 +61,7 @@ func diffFunc(cmd *cobra.Command, args []string) error {
 	cfg := &client.DiffConfig{
 		IgnoreEmpty:      ignoreEmtpy,
 		IgnoreFilePrefix: ignoreFilePrefix,
+		MatchExtension:   matchExtension,
 		Args:             args,
 	}