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[cfe/analyzer] Dot shorthands: Abstract constructors can't be instantiated or torn off.
Adding a few errors on when we instantiate or tear off abstract constructors. Should be parallel to how we currently check for these errors in the CFE and analyzer. Follow up to https://dart-review.googlesource.com/c/sdk/+/426682 Language test added, co19 test passing, and unit tests added. Bug: #59758, #59835 Change-Id: I9b34e5f960856ce50aa969ca27e56907ae3a2a8b Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/428201 Reviewed-by: Brian Wilkerson <[email protected]> Reviewed-by: Chloe Stefantsova <[email protected]> Commit-Queue: Kallen Tu <[email protected]>
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‎pkg/analyzer/lib/src/dart/resolver/property_element_resolver.dart‎

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@@ -64,6 +64,18 @@ class PropertyElementResolver with ScopeHelpers {
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_definingLibrary,
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);
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if (element != null) {
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if (!element.isFactory) {
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var enclosingElement = element.enclosingElement2;
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if (enclosingElement is ClassElementImpl2 &&
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enclosingElement.isAbstract) {
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_resolver.errorReporter.atNode(
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node,
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CompileTimeErrorCode
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.TEAROFF_OF_GENERATIVE_CONSTRUCTOR_OF_ABSTRACT_CLASS,
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);
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}
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}
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return PropertyElementResolverResult(
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readElementRequested2: element,
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getType: element.returnType,

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

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@@ -591,6 +591,24 @@ DotShorthandPropertyAccess
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''');
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}
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test_tearOff_constructor_abstract() async {
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await assertErrorsInCode(
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r'''
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Function fn() {
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return .new;
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}
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''',
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[
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error(
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CompileTimeErrorCode
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.TEAROFF_OF_GENERATIVE_CONSTRUCTOR_OF_ABSTRACT_CLASS,
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25,
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4,
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),
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],
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);
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}
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test_tearOff_constructor_new() async {
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await assertNoErrorsInCode('''
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void main() {

‎pkg/front_end/lib/src/type_inference/inference_visitor.dart‎

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@@ -12172,6 +12172,17 @@ class InferenceVisitorImpl extends InferenceVisitorBase
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node.name.text.length));
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}
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TypeDeclaration typeDeclaration = cachedContext.typeDeclaration;
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if (typeDeclaration is Class && typeDeclaration.isAbstract) {
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return new ExpressionInferenceResult(
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const DynamicType(),
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helper.buildProblem(
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templateAbstractClassInstantiation
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.withArguments(typeDeclaration.name),
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node.nameOffset,
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node.name.text.length));
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}
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// The shorthand expression is inferred in the empty context and then
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// type inference infers the type arguments.
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FunctionType functionType = constructor.function
@@ -12310,6 +12321,14 @@ class InferenceVisitorImpl extends InferenceVisitorBase
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node.name.text.length));
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}
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if (constructor is Constructor) {
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TypeDeclaration typeDeclaration = cachedContext.typeDeclaration;
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if (typeDeclaration is Class && typeDeclaration.isAbstract) {
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return new ExpressionInferenceResult(
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const DynamicType(),
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helper.buildProblem(messageAbstractClassConstructorTearOff,
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node.nameOffset, node.name.text.length));
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}
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DartType type = constructor.function
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.computeFunctionType(Nullability.nonNullable);
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Expression tearOff = new ConstructorTearOff(constructor)

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart‎

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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Function instantiation() {
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return .new(); // Error
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}
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Function tearOff() {
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return .new; // Error
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}
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void main() async {
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var iter = [1, 2];
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await for (var x in .fromIterable(iter)) { // No error.
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print(x);
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}
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}

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart.strong.expect‎

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library;
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//
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// Problems in library:
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//
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// pkg/front_end/testcases/dot_shorthands/abstract_class.dart:6:11: Error: The class 'Function' is abstract and can't be instantiated.
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// return .new(); // Error
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// ^^^
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//
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// pkg/front_end/testcases/dot_shorthands/abstract_class.dart:10:11: Error: Constructors on abstract classes can't be torn off.
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// return .new; // Error
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// ^^^
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//
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import self as self;
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import "dart:core" as core;
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import "dart:async" as asy;
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static method instantiation() → core::Function {
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return invalid-expression "pkg/front_end/testcases/dot_shorthands/abstract_class.dart:6:11: Error: The class 'Function' is abstract and can't be instantiated.
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return .new(); // Error
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^^^" as{TypeError,ForDynamic} core::Function;
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}
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static method tearOff() → core::Function {
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return invalid-expression "pkg/front_end/testcases/dot_shorthands/abstract_class.dart:10:11: Error: Constructors on abstract classes can't be torn off.
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return .new; // Error
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^^^" as{TypeError,ForDynamic} core::Function;
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}
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static method main() → void async /* emittedValueType= void */ {
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core::List<core::int> iter = <core::int>[1, 2];
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await for (core::int x in asy::Stream::fromIterable<core::int>(iter)) {
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core::print(x);
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}
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}

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart.strong.modular.expect‎

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library;
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//
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// Problems in library:
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//
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// pkg/front_end/testcases/dot_shorthands/abstract_class.dart:6:11: Error: The class 'Function' is abstract and can't be instantiated.
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// return .new(); // Error
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// ^^^
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//
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// pkg/front_end/testcases/dot_shorthands/abstract_class.dart:10:11: Error: Constructors on abstract classes can't be torn off.
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// return .new; // Error
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// ^^^
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//
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import self as self;
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import "dart:core" as core;
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import "dart:async" as asy;
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static method instantiation() → core::Function {
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return invalid-expression "pkg/front_end/testcases/dot_shorthands/abstract_class.dart:6:11: Error: The class 'Function' is abstract and can't be instantiated.
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return .new(); // Error
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^^^" as{TypeError,ForDynamic} core::Function;
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}
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static method tearOff() → core::Function {
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return invalid-expression "pkg/front_end/testcases/dot_shorthands/abstract_class.dart:10:11: Error: Constructors on abstract classes can't be torn off.
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return .new; // Error
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^^^" as{TypeError,ForDynamic} core::Function;
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}
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static method main() → void async /* emittedValueType= void */ {
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core::List<core::int> iter = <core::int>[1, 2];
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await for (core::int x in asy::Stream::fromIterable<core::int>(iter)) {
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core::print(x);
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}
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}

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart.strong.outline.expect‎

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library;
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import self as self;
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import "dart:core" as core;
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static method instantiation() → core::Function
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;
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static method tearOff() → core::Function
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;
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static method main() → void async
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;

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart.strong.transformed.expect‎

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library;
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//
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// Problems in library:
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//
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// pkg/front_end/testcases/dot_shorthands/abstract_class.dart:6:11: Error: The class 'Function' is abstract and can't be instantiated.
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// return .new(); // Error
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// ^^^
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//
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// pkg/front_end/testcases/dot_shorthands/abstract_class.dart:10:11: Error: Constructors on abstract classes can't be torn off.
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// return .new; // Error
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// ^^^
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//
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import self as self;
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import "dart:core" as core;
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import "dart:async" as asy;
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static method instantiation() → core::Function {
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return invalid-expression "pkg/front_end/testcases/dot_shorthands/abstract_class.dart:6:11: Error: The class 'Function' is abstract and can't be instantiated.
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return .new(); // Error
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^^^" as{TypeError,ForDynamic} core::Function;
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}
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static method tearOff() → core::Function {
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return invalid-expression "pkg/front_end/testcases/dot_shorthands/abstract_class.dart:10:11: Error: Constructors on abstract classes can't be torn off.
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return .new; // Error
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^^^" as{TypeError,ForDynamic} core::Function;
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}
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static method main() → void async /* emittedValueType= void */ {
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core::List<core::int> iter = core::_GrowableList::_literal2<core::int>(1, 2);
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{
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synthesized asy::Stream<core::int> :stream = asy::Stream::fromIterable<core::int>(iter);
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synthesized asy::_StreamIterator<core::int>? :for-iterator = new asy::_StreamIterator::•<core::int>(:stream);
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try
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while (let dynamic #t1 = asy::_asyncStarMoveNextHelper(:stream) in await :for-iterator.{asy::_StreamIterator::moveNext}(){() → asy::Future<core::bool>}) {
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core::int x = :for-iterator.{asy::_StreamIterator::current}{core::int};
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{
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core::print(x);
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}
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}
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finally
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if(!(:for-iterator.{asy::_StreamIterator::_subscription}{asy::StreamSubscription<core::int>?} == null))
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await :for-iterator.{asy::_StreamIterator::cancel}(){() → asy::Future<dynamic>};
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}
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}

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart.textual_outline.expect‎

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Function instantiation() {}
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Function tearOff() {}
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void main() async {}

‎pkg/front_end/testcases/dot_shorthands/abstract_class.dart.textual_outline_modelled.expect‎

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Function instantiation() {}
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Function tearOff() {}
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void main() async {}

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