Migration: fix handling of unresolved field formal parameters.

Change-Id: I67d3472974657618afa88d7feafae1eaf8250e43
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/207040
Reviewed-by: Samuel Rawlins <srawlins@google.com>

pkg/nnbd_migration/lib/src/edge_builder.dart

@@ -895,18 +895,20 @@ class EdgeBuilder extends GeneralizingAstVisitor<DecoratedType>
     _dispatch(node.parameters);
     var parameterElement = node.declaredElement as FieldFormalParameterElement;
     var parameterType = _variables!.decoratedElementType(parameterElement);
-    var field = parameterElement.field!;
-    _fieldsNotInitializedByConstructor!.remove(field);
-    var fieldType = _variables!.decoratedElementType(field);
-    var origin = FieldFormalParameterOrigin(source, node);
-    if (node.type == null) {
-      _linkDecoratedTypes(parameterType, fieldType, origin, isUnion: false);
-      _checkAssignment(origin, FixReasonTarget.root,
-          source: fieldType, destination: parameterType, hard: false);
-    } else {
-      _dispatch(node.type);
-      _checkAssignment(origin, FixReasonTarget.root,
-          source: parameterType, destination: fieldType, hard: true);
+    var field = parameterElement.field;
+    if (field != null) {
+      _fieldsNotInitializedByConstructor!.remove(field);
+      var fieldType = _variables!.decoratedElementType(field);
+      var origin = FieldFormalParameterOrigin(source, node);
+      if (node.type == null) {
+        _linkDecoratedTypes(parameterType, fieldType, origin, isUnion: false);
+        _checkAssignment(origin, FixReasonTarget.root,
+            source: fieldType, destination: parameterType, hard: false);
+      } else {
+        _dispatch(node.type);
+        _checkAssignment(origin, FixReasonTarget.root,
+            source: parameterType, destination: fieldType, hard: true);
+      }
     }
 
     return null;
@@ -2083,7 +2085,10 @@ class EdgeBuilder extends GeneralizingAstVisitor<DecoratedType>
     var result = <PropertyAccessorElement, FieldFormalParameterElement>{};
     for (var parameter in constructorElement.parameters) {
       if (parameter is FieldFormalParameterElement) {
-        result[parameter.field!.getter!] = parameter;
+        var getter = parameter.field?.getter;
+        if (getter != null) {
+          result[getter] = parameter;
+        }
       }
     }
     return result;

pkg/nnbd_migration/lib/src/fix_builder.dart

@@ -1147,15 +1147,18 @@ class _FixBuilderPreVisitor extends GeneralizingAstVisitor<void>
       // Potentially add an explicit type to a field formal parameter.
       var decl = node.declaredElement as FieldFormalParameterElement;
       var decoratedType = _fixBuilder._variables!.decoratedElementType(decl);
-      var decoratedFieldType =
-          _fixBuilder._variables!.decoratedElementType(decl.field!);
-      var typeToAdd = _fixBuilder._variables!.toFinalType(decoratedType);
-      var fieldFinalType =
-          _fixBuilder._variables!.toFinalType(decoratedFieldType);
-      if (typeToAdd is InterfaceType &&
-          !_fixBuilder._typeSystem.isSubtypeOf(fieldFinalType, typeToAdd)) {
-        (_fixBuilder._getChange(node) as NodeChangeForFieldFormalParameter)
-            .addExplicitType = typeToAdd;
+      var field = decl.field;
+      if (field != null) {
+        var decoratedFieldType =
+            _fixBuilder._variables!.decoratedElementType(field);
+        var typeToAdd = _fixBuilder._variables!.toFinalType(decoratedType);
+        var fieldFinalType =
+            _fixBuilder._variables!.toFinalType(decoratedFieldType);
+        if (typeToAdd is InterfaceType &&
+            !_fixBuilder._typeSystem.isSubtypeOf(fieldFinalType, typeToAdd)) {
+          (_fixBuilder._getChange(node) as NodeChangeForFieldFormalParameter)
+              .addExplicitType = typeToAdd;
+        }
       }
     } else if (node.parameters != null) {
       // Handle function-typed field formal parameters.

pkg/nnbd_migration/lib/src/node_builder.dart

@@ -446,9 +446,10 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
 
   @override
   DecoratedType? visitMethodDeclaration(MethodDeclaration node) {
-    _handleExecutableDeclaration(
+    var declaredElement = node.declaredElement;
+    var decoratedType = _handleExecutableDeclaration(
         node,
-        node.declaredElement!,
+        declaredElement!,
         node.metadata,
         node.returnType,
         node.typeParameters,
@@ -456,6 +457,19 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
         null,
         node.body,
         null);
+    if (declaredElement is PropertyAccessorElement) {
+      // Store a decorated type for the synthetic field so that in case we try
+      // to access it later we won't crash (this could happen due to errors in
+      // the source code).
+      if (declaredElement.isGetter) {
+        _variables!.recordDecoratedElementType(
+            declaredElement.variable, decoratedType.returnType);
+      } else {
+        _variables!.recordDecoratedElementType(
+            declaredElement.variable, decoratedType.positionalParameters![0],
+            soft: true);
+      }
+    }
     return null;
   }
 
@@ -675,7 +689,7 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
   }
 
   /// Common handling of function and method declarations.
-  void _handleExecutableDeclaration(
+  DecoratedType _handleExecutableDeclaration(
       AstNode node,
       ExecutableElement declaredElement,
       NodeList<Annotation>? metadata,
@@ -726,6 +740,7 @@ class NodeBuilder extends GeneralizingAstVisitor<DecoratedType>
     }
     _variables!
         .recordDecoratedElementType(declaredElement, decoratedFunctionType);
+    return decoratedFunctionType;
   }
 
   DecoratedType? _handleFormalParameter(

pkg/nnbd_migration/lib/src/variables.dart

@@ -214,7 +214,8 @@ class Variables {
   }
 
   /// Associates decorated type information with the given [element].
-  void recordDecoratedElementType(Element? element, DecoratedType? type) {
+  void recordDecoratedElementType(Element? element, DecoratedType? type,
+      {bool soft = false}) {
     assert(() {
       assert(element is! TypeParameterElement,
           'Use recordDecoratedTypeParameterBound instead');
@@ -227,6 +228,9 @@ class Variables {
       }
       return true;
     }());
+    if (soft && _decoratedElementTypes.containsKey(element)) {
+      return;
+    }
     _decoratedElementTypes[element] = type;
   }
 

pkg/nnbd_migration/test/api_test.dart

@@ -116,7 +116,7 @@ abstract class _ProvisionalApiTestBase extends AbstractContextTest {
   ///
   /// Optional parameter [removeViaComments] indicates whether dead code should
   /// be removed in its entirety (the default) or removed by commenting it out.
-  Future<void> _checkSingleFileChanges(String content, String expected,
+  Future<void> _checkSingleFileChanges(String content, dynamic expected,
       {Map<String, String> migratedInput = const {},
       bool removeViaComments = false,
       bool warnOnWeakCode = false,
@@ -1164,6 +1164,41 @@ void main() {
     await _checkSingleFileChanges(content, expected);
   }
 
+  Future<void> test_constructor_field_formal_resolves_to_getter() async {
+    var content = '''
+class C {
+  int get i => 0;
+  C(this.i);
+}
+''';
+    // It doesn't matter what the migration produces; we just want to make sure
+    // there isn't a crash.
+    await _checkSingleFileChanges(content, anything, allowErrors: true);
+  }
+
+  Future<void> test_constructor_field_formal_resolves_to_setter() async {
+    var content = '''
+class C {
+  set i(int value) {}
+  C(this.i);
+}
+''';
+    // It doesn't matter what the migration produces; we just want to make sure
+    // there isn't a crash.
+    await _checkSingleFileChanges(content, anything, allowErrors: true);
+  }
+
+  Future<void> test_constructor_field_formal_unresolved() async {
+    var content = '''
+class C {
+  C(this.i);
+}
+''';
+    // It doesn't matter what the migration produces; we just want to make sure
+    // there isn't a crash.
+    await _checkSingleFileChanges(content, anything, allowErrors: true);
+  }
+
   Future<void> test_constructor_optional_param_factory() async {
     var content = '''
 class C {