Issue 25914. Fix for compound assignments like 'T += T'.

pkg/analyzer/lib/src/task/strong/checker.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.checker;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 604 matching lines @@
       var functionType = methodElement.type;
       var paramTypes = functionType.normalParameterTypes;
       assert(paramTypes.length == 1);
       assert(functionType.namedParameterTypes.isEmpty);
       assert(functionType.optionalParameterTypes.isEmpty);
 
       // Check the LHS type.
       var staticInfo;
       var rhsType = _getStaticType(expr.rightHandSide);
       var lhsType = _getStaticType(expr.leftHandSide);
-      var returnType = _specializedBinaryReturnType(
-          op, lhsType, rhsType, functionType.returnType);
+      var returnType = rules.refineBinaryExpressionType(
+          typeProvider, lhsType, op, rhsType, functionType.returnType);
 
       if (!rules.isSubtypeOf(returnType, lhsType)) {
         final numType = typeProvider.numType;
         // Try to fix up the numerical case if possible.
         if (rules.isSubtypeOf(lhsType, numType) &&
             rules.isSubtypeOf(lhsType, rhsType)) {
           // This is also slightly different from spec, but allows us to keep
           // compound operators in the int += num and num += dynamic cases.
           staticInfo =
               DownCast.create(rules, expr.rightHandSide, rhsType, lhsType);
@@ skipping 277 matching lines @@
 
     if (info is CoercionInfo) {
       // TODO(jmesserly): if we're run again on the same AST, we'll produce the
       // same annotations. This should be harmless. This might go away once
       // CodeChecker is integrated better with analyzer, as it will know that
       // checking has already been performed.
       // assert(CoercionInfo.get(info.node) == null);
       CoercionInfo.set(info.node, info);
     }
   }
-
-  DartType _specializedBinaryReturnType(
-      TokenType op, DartType t1, DartType t2, DartType normalReturnType) {
-    // This special cases binary return types as per 16.26 and 16.27 of the
-    // Dart language spec.
-    switch (op) {
-      case TokenType.PLUS:
-      case TokenType.MINUS:
-      case TokenType.STAR:
-      case TokenType.TILDE_SLASH:
-      case TokenType.PERCENT:
-      case TokenType.PLUS_EQ:
-      case TokenType.MINUS_EQ:
-      case TokenType.STAR_EQ:
-      case TokenType.TILDE_SLASH_EQ:
-      case TokenType.PERCENT_EQ:
-        if (t1 == typeProvider.intType && t2 == typeProvider.intType) return t1;
-        if (t1 == typeProvider.doubleType && t2 == typeProvider.doubleType)
-          return t1;
-        // This particular combo is not spelled out in the spec, but all
-        // implementations and analyzer seem to follow this.
-        if (t1 == typeProvider.doubleType && t2 == typeProvider.intType)
-          return t1;
-    }
-    return normalReturnType;
-  }
 }
 
 /// Checks for overriding declarations of fields and methods. This is used to
 /// check overrides between classes and superclasses, interfaces, and mixin
 /// applications.
 class _OverrideChecker {
   bool _failure = false;
   final StrongTypeSystemImpl rules;
   final TypeProvider _typeProvider;
   final AnalysisErrorListener _reporter;
@@ skipping 332 matching lines @@
     } while (!current.isObject && !visited.contains(current));
   }
 
   void _recordMessage(StaticInfo info) {
     if (info == null) return;
     var error = info.toAnalysisError();
     if (error.errorCode.errorSeverity == ErrorSeverity.ERROR) _failure = true;
     _reporter.onError(error);
   }
 }