fix #25794, infer parameter type from default value, in AST summaries

pkg/analyzer/lib/src/summary/summarize_ast.dart

 // Copyright (c) 2016, 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.
 
 library serialization.summarize_ast;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/type.dart' show DartType;
@@ skipping 625 matching lines @@
         serializeTypeParameters(typeParameters, typeParameterScope);
     if (!isTopLevel) {
       b.isStatic = isDeclaredStatic;
     }
     b.returnType = serializeTypeName(returnType);
     bool isSemanticallyStatic = isTopLevel || isDeclaredStatic;
     if (formalParameters != null) {
       b.parameters = formalParameters.parameters
           .map((FormalParameter p) => p.accept(this))
           .toList();
-      if (!isSemanticallyStatic) {
-        for (int i = 0; i < formalParameters.parameters.length; i++) {
-          if (!b.parameters[i].isFunctionTyped &&
-              b.parameters[i].type == null) {
-            b.parameters[i].inferredTypeSlot = assignSlot();
+
+      for (int i = 0; i < formalParameters.parameters.length; i++) {
+        UnlinkedParamBuilder p = b.parameters[i];
+        if (!p.isFunctionTyped && p.type == null) {
+          // Strong mode infers parameters in two cases:
+          // - instance members (i.e. not semantically static),
+          // - parameters with default values, except initializing formals
+          //   (the type comes from the field).
+          if (!isSemanticallyStatic ||
+              p.initializer != null && !p.isInitializingFormal) {
+            p.inferredTypeSlot = assignSlot();
           }
         }
       }
     }
     b.documentationComment = serializeDocumentation(documentationComment);
     b.annotations = serializeAnnotations(annotations);
     b.codeRange = serializeCodeRange(node);
     if (returnType == null && !isSemanticallyStatic) {
       b.inferredReturnTypeSlot = assignSlot();
     }
@@ skipping 715 matching lines @@
 /**
  * A [_TypeParameterScope] is a [_Scope] which defines [_ScopedTypeParameter]s.
  */
 class _TypeParameterScope extends _Scope {
   /**
    * Get the number of [_ScopedTypeParameter]s defined in this
    * [_TypeParameterScope].
    */
   int get length => _definedNames.length;
 }