Extension type. Issue 54080. The result of == is always 'bool'.

Bug: #54080
Change-Id: I5deff67f480b24dc719d438bc7df5a7697772bee
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/337281
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

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

@@ -391,7 +391,9 @@ class BinaryExpressionResolver {
     }
 
     var staticType = node.staticInvokeType?.returnType;
-    if (leftType is DynamicType) {
+    if (node.operator.type == TokenType.EQ_EQ) {
+      staticType = _typeSystem.typeProvider.boolType;
+    } else if (leftType is DynamicType) {
       staticType ??= DynamicTypeImpl.instance;
     } else {
       staticType ??= InvalidTypeImpl.instance;

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

@@ -17,6 +17,37 @@ main() {
 @reflectiveTest
 class BinaryExpressionResolutionTest extends PubPackageResolutionTest
     with BinaryExpressionResolutionTestCases {
+  test_eqEq_alwaysBool() async {
+    await assertNoErrorsInCode(r'''
+extension type MyBool(bool it) implements bool {}
+
+class A {
+  MyBool operator ==(_) => MyBool(true);
+}
+
+void f(A a) {
+  a == 0;
+}
+''');
+
+    final node = findNode.binary('a == 0');
+    assertResolvedNodeText(node, r'''
+BinaryExpression
+  leftOperand: SimpleIdentifier
+    token: a
+    staticElement: self::@function::f::@parameter::a
+    staticType: A
+  operator: ==
+  rightOperand: IntegerLiteral
+    literal: 0
+    parameter: self::@class::A::@method::==::@parameter::_
+    staticType: int
+  staticElement: self::@class::A::@method::==
+  staticInvokeType: MyBool Function(Object)
+  staticType: bool
+''');
+  }
+
   test_eqEq_switchExpression_left() async {
     await assertNoErrorsInCode(r'''
 void f(Object? x) {
@@ -742,7 +773,7 @@ BinaryExpression
     staticType: int
   staticElement: <null>
   staticInvokeType: null
-  staticType: InvalidType
+  staticType: bool
 ''');
   }