Type inference for StringConcatenation.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

 // Copyright (c) 2017, 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.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 482 matching lines @@
 }
 
 /// Concrete shadow object representing a string concatenation in kernel form.
 class KernelStringConcatenation extends StringConcatenation
     implements KernelExpression {
   KernelStringConcatenation(List<Expression> expressions) : super(expressions);
 
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
-    // TODO(scheglov) Add and use inferStringConcatenation() instead.
-    return inferrer.inferStringLiteral(typeContext, typeNeeded);
+    return inferrer.inferStringConcatenation(
+        typeContext, typeNeeded, expressions);
   }
 }
 
 /// Concrete shadow object representing a string literal in kernel form.
 class KernelStringLiteral extends StringLiteral implements KernelExpression {
   KernelStringLiteral(String value) : super(value);
 
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
@@ skipping 363 matching lines @@
       // KernelVariableDeclaration.
       mutatedInClosure = true;
       declaredType = variable.type;
     }
     return inferrer.inferVariableGet(typeContext, typeNeeded, mutatedInClosure,
         _fact, _scope, fileOffset, declaredType, (type) {
       promotedType = type;
     });
   }
 }