promslog: Only log basename, not full path

Signed-off-by: Julien <roidelapluie@o11y.eu>

promslog/slog.go

@@ -66,6 +66,17 @@ var (
 		default:
 		}
 
+		return a
+	}
+	truncateSourceAttrFunc = func(groups []string, a slog.Attr) slog.Attr {
+		if a.Key != slog.SourceKey {
+			return a
+		}
+
+		if src, ok := a.Value.Any().(*slog.Source); ok {
+			a.Value = slog.StringValue(filepath.Base(src.File) + ":" + strconv.Itoa(src.Line))
+		}
+
 		return a
 	}
 )
@@ -165,8 +176,9 @@ func New(config *Config) *slog.Logger {
 	}
 
 	logHandlerOpts := &slog.HandlerOptions{
-		Level:     config.Level.lvl,
-		AddSource: true,
+		Level:       config.Level.lvl,
+		AddSource:   true,
+		ReplaceAttr: truncateSourceAttrFunc,
 	}
 
 	if config.Style == GoKitStyle {

promslog/slog_test.go

@@ -146,3 +146,47 @@ func TestDynamicLevels(t *testing.T) {
 		})
 	}
 }
+
+func TestTruncateSourceFileName_DefaultStyle(t *testing.T) {
+	var buf bytes.Buffer
+
+	config := &Config{
+		Writer: &buf,
+	}
+
+	logger := New(config)
+	logger.Info("test message")
+
+	output := buf.String()
+
+	if !strings.Contains(output, "source=slog_test.go:") {
+		t.Errorf("Expected source file name to be truncated to basename, got: %s", output)
+	}
+
+	if strings.Contains(output, "/") {
+		t.Errorf("Expected no directory separators in source file name, got: %s", output)
+	}
+}
+
+func TestTruncateSourceFileName_GoKitStyle(t *testing.T) {
+	var buf bytes.Buffer
+
+	config := &Config{
+		Writer: &buf,
+		Style:  GoKitStyle,
+	}
+
+	logger := New(config)
+	logger.Info("test message")
+
+	output := buf.String()
+
+	// In GoKitStyle, the source key is "caller".
+	if !strings.Contains(output, "caller=slog_test.go:") {
+		t.Errorf("Expected caller to contain basename of source file, got: %s", output)
+	}
+
+	if strings.Contains(output, "/") {
+		t.Errorf("Expected no directory separators in caller, got: %s", output)
+	}
+}