fix: use newline-aware trimming in diff() for backward compatibility

Preserve newlines during whitespace trimming so diff() can detect
whether output contains multiple lines. When newlines are present,
split by newline (handles filenames with spaces). When absent, fall
back to strings.Fields() for backward compat with custom diff commands
that return a single filename without a trailing newline.

Author: siredmar

pipeline.go

@@ -105,17 +105,21 @@ func diff(command string) ([]string, error) {
 		return nil, fmt.Errorf("diff command failed: %v", err)
 	}
 
-	trimmed := strings.TrimSpace(output)
+	trimmed := strings.Trim(output, " \t\r\v\f")
 	if trimmed == "" {
-		return nil, nil
+		return []string{}, nil
 	}
 
 	var fields []string
-	for _, line := range strings.Split(trimmed, "\n") {
-		line = strings.TrimSpace(line)
-		if line != "" {
-			fields = append(fields, line)
+	if strings.Contains(trimmed, "\n") {
+		for _, line := range strings.Split(trimmed, "\n") {
+			line = strings.TrimSpace(line)
+			if line != "" {
+				fields = append(fields, line)
+			}
 		}
+	} else {
+		fields = strings.Fields(trimmed)
 	}
 
 	paths := make([]string, 0, len(fields))

pipeline_test.go

@@ -120,7 +120,7 @@ func TestDiffWithQuotedPaths(t *testing.T) {
 		"projects/test/pages/17_🪁_testfile.py",
 		"normal/file.txt",
 	}
-	got, err := diff(`printf '"projects/test/pages/17_\360\237\252\201_testfile.py"\nnormal/file.txt'`)
+	got, err := diff(`printf '"projects/test/pages/17_\360\237\252\201_testfile.py"\nnormal/file.txt\n'`)
 	assert.NoError(t, err)
 	assert.Equal(t, want, got)
 }
@@ -135,7 +135,7 @@ func TestDiffWithSpacesInFilenames(t *testing.T) {
 	}
 
 	// printf produces newline-separated output, just like git diff --name-only
-	got, err := diff(`printf 'directory/File Name With Spaces.md\nanother dir/some file.txt\nno-spaces.go'`)
+	got, err := diff(`printf 'directory/File Name With Spaces.md\nanother dir/some file.txt\nno-spaces.go\n'`)
 	assert.NoError(t, err)
 	assert.Equal(t, want, got)
 }
@@ -145,7 +145,7 @@ func TestDiffSingleFile(t *testing.T) {
 		"services/foo/serverless.yml",
 	}
 
-	got, err := diff(`printf 'services/foo/serverless.yml'`)
+	got, err := diff(`printf 'services/foo/serverless.yml\n'`)
 	assert.NoError(t, err)
 	assert.Equal(t, want, got)
 }
@@ -156,7 +156,7 @@ func TestDiffWithSpacesInFilenamesSingleFile(t *testing.T) {
 	}
 
 	// printf produces newline-separated output, just like git diff --name-only
-	got, err := diff(`printf 'directory/File Name With Spaces.md'`)
+	got, err := diff(`printf 'directory/File Name With Spaces.md\n'`)
 	assert.NoError(t, err)
 	assert.Equal(t, want, got)
 }