fix(static-msg): support binary expressions

sloglint.go

@@ -239,15 +239,19 @@
 	}
 
 	msgPos := funcInfo.argsPos - 1
+
 	// NOTE: "With" functions have no message argument and must be skipped.
 	if opts.StaticMsg && msgPos >= 0 && !isStaticMsg(call.Args[msgPos]) {
 		pass.Reportf(call.Pos(), "message should be a string literal or a constant")
 	}
 
 	if opts.MsgStyle != "" && msgPos >= 0 {
-		if msg, ok := call.Args[msgPos].(*ast.BasicLit); ok && msg.Kind == token.STRING {
-			msg.Value = msg.Value[1 : len(msg.Value)-1] // trim quotes/backticks.
-			if ok := isValidMsgStyle(msg.Value, opts.MsgStyle); !ok {
+		if lit, ok := call.Args[msgPos].(*ast.BasicLit); ok && lit.Kind == token.STRING {
+			value, err := strconv.Unquote(lit.Value)
+			if err != nil {
+				panic("unreachable") // string literals are always quoted.
+			}
+			if ok := isValidMsgStyle(value, opts.MsgStyle); !ok {
 				pass.Reportf(call.Pos(), "message should be %s", opts.MsgStyle)
 			}
 		}
@@ -267,7 +271,6 @@
 		if typ == nil {
 			continue
 		}
-
 		switch typ.String() {
 		case "string":
 			keys = append(keys, args[i])
@@ -376,6 +379,11 @@
 		return msg.Kind == token.STRING
 	case *ast.Ident: // e.g. const msg = "msg"; slog.Info(msg)
 		return msg.Obj != nil && msg.Obj.Kind == ast.Con
+	case *ast.BinaryExpr: // e.g. slog.Info("x" + "y")
+		if msg.Op != token.ADD {
+			panic("unreachable") // only + can be applied to strings.
+		}
+		return isStaticMsg(msg.X) && isStaticMsg(msg.Y)
 	default:
 		return false
 	}
@@ -455,10 +463,9 @@
 		}
 	}
 	if lit, ok := key.(*ast.BasicLit); ok && lit.Kind == token.STRING {
-		// string literals are always quoted.
 		value, err := strconv.Unquote(lit.Value)
 		if err != nil {
-			panic("unreachable")
+			panic("unreachable") // string literals are always quoted.
 		}
 		return value, true
 	}

testdata/src/static_msg/static_msg.go

@@ -23,13 +23,21 @@ func tests() {
 	slog.Log(ctx, slog.LevelInfo, constMsg)
 	slog.With("key", "value").Info(constMsg)
 
+	slog.Info(varMsg)                      // want `message should be a string literal or a constant`
+	slog.InfoContext(ctx, varMsg)          // want `message should be a string literal or a constant`
+	slog.Log(ctx, slog.LevelInfo, varMsg)  // want `message should be a string literal or a constant`
+	slog.With("key", "value").Info(varMsg) // want `message should be a string literal or a constant`
+
 	slog.Info(fmt.Sprintf("msg"))                      // want `message should be a string literal or a constant`
 	slog.InfoContext(ctx, fmt.Sprintf("msg"))          // want `message should be a string literal or a constant`
 	slog.Log(ctx, slog.LevelInfo, fmt.Sprintf("msg"))  // want `message should be a string literal or a constant`
 	slog.With("key", "value").Info(fmt.Sprintf("msg")) // want `message should be a string literal or a constant`
 
-	slog.Info(varMsg)                      // want `message should be a string literal or a constant`
-	slog.InfoContext(ctx, varMsg)          // want `message should be a string literal or a constant`
-	slog.Log(ctx, slog.LevelInfo, varMsg)  // want `message should be a string literal or a constant`
-	slog.With("key", "value").Info(varMsg) // want `message should be a string literal or a constant`
+	// binary expressions:
+	slog.Info("msg" + "msg")
+	slog.Info("msg" + "msg" + "msg")
+	slog.Info("msg" + constMsg)
+	slog.Info("msg" + varMsg)                                 // want `message should be a string literal or a constant`
+	slog.Info("msg" + fmt.Sprintf("msg"))                     // want `message should be a string literal or a constant`
+	slog.Info("msg" + constMsg + varMsg + fmt.Sprintf("msg")) // want `message should be a string literal or a constant`
 }