Issue 49106. Update the context type for index in read/write.

Bug: https://github.com/dart-lang/sdk/issues/49106
Change-Id: I522269360c6664ac4a9129cb71bf378c9dfca812
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/256647
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/src/dart/element/extensions.dart

@@ -6,6 +6,7 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
+import 'package:collection/collection.dart';
 import 'package:meta/meta_meta.dart';
 
 extension ElementAnnotationExtensions on ElementAnnotation {
@@ -109,6 +110,16 @@ extension ExecutableElementExtension on ExecutableElement {
   }
 }
 
+extension ExecutableElementExtensionQuestion on ExecutableElement? {
+  DartType? get firstParameterType {
+    final self = this;
+    if (self is MethodElement) {
+      return self.parameters.firstOrNull?.type;
+    }
+    return null;
+  }
+}
+
 extension ParameterElementExtensions on ParameterElement {
   /// Return [ParameterElement] with the specified properties replaced.
   ParameterElement copyWith({

pkg/analyzer/lib/src/dart/resolver/property_element_resolver.dart

@@ -67,7 +67,11 @@ class PropertyElementResolver with ScopeHelpers {
         );
       }
 
-      return _toIndexResult(result);
+      return _toIndexResult(
+        result,
+        hasRead: hasRead,
+        hasWrite: hasWrite,
+      );
     }
 
     var targetType = target.typeOrThrow;
@@ -127,7 +131,11 @@ class PropertyElementResolver with ScopeHelpers {
       );
     }
 
-    return _toIndexResult(result);
+    return _toIndexResult(
+      result,
+      hasRead: hasRead,
+      hasWrite: hasWrite,
+    );
   }
 
   PropertyElementResolverResult resolvePrefixedIdentifier({
@@ -328,20 +336,6 @@ class PropertyElementResolver with ScopeHelpers {
     }
   }
 
-  DartType? _computeIndexContextType({
-    required ExecutableElement? readElement,
-    required ExecutableElement? writeElement,
-  }) {
-    var method = writeElement ?? readElement;
-    var parameters = method is MethodElement ? method.parameters : null;
-
-    if (parameters != null && parameters.isNotEmpty) {
-      return parameters[0].type;
-    }
-
-    return null;
-  }
-
   bool _isAccessible(ExecutableElement element) {
     return element.isAccessibleIn2(_definingLibrary);
   }
@@ -848,17 +842,22 @@ class PropertyElementResolver with ScopeHelpers {
     );
   }
 
-  PropertyElementResolverResult _toIndexResult(ResolutionResult result) {
+  PropertyElementResolverResult _toIndexResult(
+    ResolutionResult result, {
+    required bool hasRead,
+    required bool hasWrite,
+  }) {
     var readElement = result.getter;
     var writeElement = result.setter;
 
+    final contextType = hasRead
+        ? readElement.firstParameterType
+        : writeElement.firstParameterType;
+
     return PropertyElementResolverResult(
       readElementRequested: readElement,
       writeElementRequested: writeElement,
-      indexContextType: _computeIndexContextType(
-        readElement: readElement,
-        writeElement: writeElement,
-      ),
+      indexContextType: contextType,
     );
   }
 }

pkg/analyzer/lib/src/generated/resolver.dart

@@ -787,7 +787,7 @@ class ResolverVisitor extends ThrowingAstVisitor<void>
       var whyNotPromoted = flowAnalysis.flow?.whyNotPromoted(node.index);
       checkIndexExpressionIndex(
         node.index,
-        readElement: result.readElement as ExecutableElement?,
+        readElement: hasRead ? result.readElement as ExecutableElement? : null,
         writeElement: result.writeElement as ExecutableElement?,
         whyNotPromoted: whyNotPromoted,
       );

pkg/analyzer/test/src/dart/resolution/index_expression_test.dart

@@ -2,6 +2,7 @@
 // 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.
 
+import 'package:analyzer/src/error/codes.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'context_collection_resolution.dart';
@@ -14,6 +15,136 @@ main() {
 
 @reflectiveTest
 class IndexExpressionTest extends PubPackageResolutionTest {
+  test_contextType_read() async {
+    await assertNoErrorsInCode(r'''
+class A {
+  bool operator [](int index) => false;
+  operator []=(String index, bool value) {}
+}
+
+void f(A a) {
+  a[ g() ];
+}
+
+T g<T>() => throw 0;
+''');
+
+    var node = findNode.methodInvocation('g()');
+    assertResolvedNodeText(node, r'''
+MethodInvocation
+  methodName: SimpleIdentifier
+    token: g
+    staticElement: self::@function::g
+    staticType: T Function<T>()
+  argumentList: ArgumentList
+    leftParenthesis: (
+    rightParenthesis: )
+  parameter: self::@class::A::@method::[]::@parameter::index
+  staticInvokeType: int Function()
+  staticType: int
+  typeArgumentTypes
+    int
+''');
+  }
+
+  test_contextType_readWrite_readLower() async {
+    await assertNoErrorsInCode(r'''
+class A {
+  int operator [](int index) => 0;
+  operator []=(num index, int value) {}
+}
+
+void f(A a) {
+  a[ g() ]++;
+}
+
+T g<T>() => throw 0;
+''');
+
+    var node = findNode.methodInvocation('g()');
+    assertResolvedNodeText(node, r'''
+MethodInvocation
+  methodName: SimpleIdentifier
+    token: g
+    staticElement: self::@function::g
+    staticType: T Function<T>()
+  argumentList: ArgumentList
+    leftParenthesis: (
+    rightParenthesis: )
+  parameter: self::@class::A::@method::[]=::@parameter::index
+  staticInvokeType: int Function()
+  staticType: int
+  typeArgumentTypes
+    int
+''');
+  }
+
+  test_contextType_readWrite_writeLower() async {
+    await assertErrorsInCode(r'''
+class A {
+  int operator [](num index) => 0;
+  operator []=(int index, int value) {}
+}
+
+void f(A a) {
+  a[ g() ]++;
+}
+
+T g<T>() => throw 0;
+''', [
+      error(CompileTimeErrorCode.ARGUMENT_TYPE_NOT_ASSIGNABLE, 107, 3),
+    ]);
+
+    var node = findNode.methodInvocation('g()');
+    assertResolvedNodeText(node, r'''
+MethodInvocation
+  methodName: SimpleIdentifier
+    token: g
+    staticElement: self::@function::g
+    staticType: T Function<T>()
+  argumentList: ArgumentList
+    leftParenthesis: (
+    rightParenthesis: )
+  parameter: self::@class::A::@method::[]=::@parameter::index
+  staticInvokeType: num Function()
+  staticType: num
+  typeArgumentTypes
+    num
+''');
+  }
+
+  test_contextType_write() async {
+    await assertNoErrorsInCode(r'''
+class A {
+  bool operator [](int index) => false;
+  operator []=(String index, bool value) {}
+}
+
+void f(A a) {
+  a[ g() ] = true;
+}
+
+T g<T>() => throw 0;
+''');
+
+    var node = findNode.methodInvocation('g()');
+    assertResolvedNodeText(node, r'''
+MethodInvocation
+  methodName: SimpleIdentifier
+    token: g
+    staticElement: self::@function::g
+    staticType: T Function<T>()
+  argumentList: ArgumentList
+    leftParenthesis: (
+    rightParenthesis: )
+  parameter: self::@class::A::@method::[]=::@parameter::index
+  staticInvokeType: String Function()
+  staticType: String
+  typeArgumentTypes
+    String
+''');
+  }
+
   test_invalid_inDefaultValue_nullAware() async {
     await assertInvalidTestCode(r'''
 void f({a = b?[0]}) {}

pkg/nnbd_migration/test/api_test.dart

@@ -6586,7 +6586,6 @@ main() {
     await _checkSingleFileChanges(content, expected);
   }
 
-  @FailingTest(issue: 'https://github.com/dart-lang/sdk/issues/49106')
   Future<void> test_map_read_does_not_require_index_cast() async {
     var content = '''
 int f(Map<String, int> m, Object o) => m[o];

pkg/nnbd_migration/test/fix_builder_test.dart

@@ -457,7 +457,6 @@ _f(_C/*?*/ c) => c['foo'] += 0;
         changes: {findNode.simple('c['): isNullCheck});
   }
 
-  @FailingTest(reason: 'TODO(paulberry): decide if this is worth caring about')
   Future<void>
       test_assignmentTarget_indexExpression_compound_simple_check_rhs() async {
     await analyze('''
@@ -483,7 +482,6 @@ _f(_C<int, String> c) => c['foo'] += 1;
     visitAssignmentTarget(findNode.index('c['), 'int', 'int');
   }
 
-  @FailingTest(reason: 'TODO(paulberry): decide if this is worth caring about')
   Future<void>
       test_assignmentTarget_indexExpression_compound_substituted_check_rhs() async {
     await analyze('''