[cfe] Don't mark external methods as abstract

Closes #31233
Related to flutter/flutter#62887

Change-Id: I96e5a1b8045f75f1ad02fb47e5e41fe402dc3dc1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/157481
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Jens Johansen <jensj@google.com>

pkg/front_end/lib/src/fasta/builder/field_builder.dart

@@ -1410,7 +1410,7 @@ class AbstractOrExternalFieldEncoding implements FieldEncoding {
     _getter
       ..isStatic = !isInstanceMember
       ..isExtensionMember = isExtensionMember
-      ..isAbstract = isAbstract
+      ..isAbstract = isAbstract && !isExternal
       ..isExternal = isExternal;
     // TODO(johnniwinther): How can the name already have been computed?
     _getter.name ??= new Name(getterName, libraryBuilder.library);
@@ -1428,7 +1428,7 @@ class AbstractOrExternalFieldEncoding implements FieldEncoding {
       _setter
         ..isStatic = !isInstanceMember
         ..isExtensionMember = isExtensionMember
-        ..isAbstract = isAbstract
+        ..isAbstract = isAbstract && !isExternal
         ..isExternal = isExternal;
       // TODO(johnniwinther): How can the name already have been computed?
       _setter?.name ??= new Name(setterName, libraryBuilder.library);

pkg/front_end/lib/src/fasta/modifier.dart

@@ -51,7 +51,7 @@ const int initializingFormalMask = hasInitializerMask << 1;
 const int declaresConstConstructorMask = initializingFormalMask << 1;
 
 /// Not a real modifier, and by setting it to zero, it is automatically ignored
-/// by [Modifier.validate] below.
+/// by [Modifier.toMask] below.
 const int varMask = 0;
 
 const Modifier Abstract = const Modifier(ModifierEnum.Abstract, abstractMask);
@@ -90,10 +90,8 @@ class Modifier {
 
   toString() => "modifier(${'$kind'.substring('ModifierEnum.'.length)})";
 
-  static int validate(List<Modifier> modifiers, {bool isAbstract: false}) {
-    // TODO(ahe): Rename this method, validation is now taken care of by the
-    // parser.
-    int result = isAbstract ? abstractMask : 0;
+  static int toMask(List<Modifier> modifiers) {
+    int result = 0;
     if (modifiers == null) return result;
     for (Modifier modifier in modifiers) {
       result |= modifier.mask;
@@ -108,4 +106,13 @@ class Modifier {
     if (identical('var', lexeme)) return Var.mask;
     return unhandled(lexeme, "Modifier.validateVarFinalOrConst", -1, null);
   }
+
+  /// Returns [modifier] with [abstractMask] added if [isAbstract] and
+  /// [modifiers] doesn't contain [externalMask].
+  static int addAbstractMask(int modifiers, {bool isAbstract: false}) {
+    if (isAbstract && (modifiers & externalMask) == 0) {
+      modifiers |= abstractMask;
+    }
+    return modifiers;
+  }
 }

pkg/front_end/lib/src/fasta/source/outline_builder.dart

@@ -813,9 +813,7 @@ class OutlineBuilder extends StackListenerImpl {
       }
     }
     int modifiers = pop();
-    if (isAbstract) {
-      modifiers |= abstractMask;
-    }
+    modifiers = Modifier.addAbstractMask(modifiers, isAbstract: isAbstract);
     if (nativeMethodName != null) {
       modifiers |= externalMask;
     }
@@ -1059,13 +1057,11 @@ class OutlineBuilder extends StackListenerImpl {
         isAbstract = false;
       }
     }
-    int modifiers = Modifier.validate(pop(), isAbstract: isAbstract);
+    int modifiers = Modifier.toMask(pop());
+    modifiers = Modifier.addAbstractMask(modifiers, isAbstract: isAbstract);
     if (nativeMethodName != null) {
       modifiers |= externalMask;
     }
-    if ((modifiers & externalMask) != 0) {
-      modifiers &= ~abstractMask;
-    }
     bool isConst = (modifiers & constMask) != 0;
     int varFinalOrConstOffset = pop();
     List<MetadataBuilder> metadata = pop();

pkg/front_end/testcases/general/external_method.dart

@@ -0,0 +1,11 @@
+// Copyright (c) 2020, 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.
+
+external void externalMethod();
+
+class Class {
+  external void externalMethod();
+}
+
+void main() {}

pkg/front_end/testcases/general/external_method.dart.outline.expect

@@ -0,0 +1,22 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class Class extends core::Object {
+  synthetic constructor •() → self::Class*
+    ;
+  external method externalMethod() → void;
+  abstract member-signature get _identityHashCode() → core::int*;
+  abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOf(dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOfTrue(dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOfFalse(dynamic type) → core::bool*;
+  abstract member-signature operator ==(dynamic other) → core::bool*;
+  abstract member-signature get hashCode() → core::int*;
+  abstract member-signature method toString() → core::String*;
+  abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic;
+  abstract member-signature get runtimeType() → core::Type*;
+}
+external static method externalMethod() → void;
+static method main() → void
+  ;

pkg/front_end/testcases/general/external_method.dart.strong.expect

@@ -0,0 +1,22 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class Class extends core::Object {
+  synthetic constructor •() → self::Class*
+    : super core::Object::•()
+    ;
+  external method externalMethod() → void;
+  abstract member-signature get _identityHashCode() → core::int*;
+  abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOf(dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOfTrue(dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOfFalse(dynamic type) → core::bool*;
+  abstract member-signature operator ==(dynamic other) → core::bool*;
+  abstract member-signature get hashCode() → core::int*;
+  abstract member-signature method toString() → core::String*;
+  abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic;
+  abstract member-signature get runtimeType() → core::Type*;
+}
+external static method externalMethod() → void;
+static method main() → void {}

pkg/front_end/testcases/general/external_method.dart.strong.transformed.expect

@@ -0,0 +1,22 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+class Class extends core::Object {
+  synthetic constructor •() → self::Class*
+    : super core::Object::•()
+    ;
+  external method externalMethod() → void;
+  abstract member-signature get _identityHashCode() → core::int*;
+  abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOf(dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOfTrue(dynamic type) → core::bool*;
+  abstract member-signature method _simpleInstanceOfFalse(dynamic type) → core::bool*;
+  abstract member-signature operator ==(dynamic other) → core::bool*;
+  abstract member-signature get hashCode() → core::int*;
+  abstract member-signature method toString() → core::String*;
+  abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic;
+  abstract member-signature get runtimeType() → core::Type*;
+}
+external static method externalMethod() → void;
+static method main() → void {}

pkg/front_end/testcases/general/external_method.dart.textual_outline.expect

@@ -0,0 +1,7 @@
+external void externalMethod();
+
+class Class {
+  external void externalMethod();
+}
+
+void main() {}

pkg/front_end/testcases/general/external_method.dart.textual_outline_modelled.expect

@@ -0,0 +1,6 @@
+class Class {
+  external void externalMethod();
+}
+
+external void externalMethod();
+void main() {}

pkg/front_end/testcases/general/micro.dart.outline.expect

@@ -115,8 +115,8 @@ class DynamicReceiver2 extends core::Object {
 }
 static method staticMethod() → dynamic
   ;
-external static abstract method externalStatic() → core::bool*;
-external static abstract method createBar() → self::Bar*;
+external static method externalStatic() → core::bool*;
+external static method createBar() → self::Bar*;
 static method stringArgument(dynamic x) → dynamic
   ;
 static method intArgument(dynamic x) → dynamic

pkg/front_end/testcases/general/micro.dart.strong.expect

@@ -123,8 +123,8 @@ class DynamicReceiver2 extends core::Object {
 static method staticMethod() → dynamic {
   return "sdfg";
 }
-external static abstract method externalStatic() → core::bool*;
-external static abstract method createBar() → self::Bar*;
+external static method externalStatic() → core::bool*;
+external static method createBar() → self::Bar*;
 static method stringArgument(dynamic x) → dynamic {}
 static method intArgument(dynamic x) → dynamic {}
 static method makeDynamicCall(dynamic receiver) → void {

pkg/front_end/testcases/general/micro.dart.strong.transformed.expect

@@ -123,8 +123,8 @@ class DynamicReceiver2 extends core::Object {
 static method staticMethod() → dynamic {
   return "sdfg";
 }
-external static abstract method externalStatic() → core::bool*;
-external static abstract method createBar() → self::Bar*;
+external static method externalStatic() → core::bool*;
+external static method createBar() → self::Bar*;
 static method stringArgument(dynamic x) → dynamic {}
 static method intArgument(dynamic x) → dynamic {}
 static method makeDynamicCall(dynamic receiver) → void {

pkg/front_end/testcases/general/optional.dart.outline.expect

@@ -77,6 +77,6 @@ class InvalidListener extends core::Object {
   abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic;
   abstract member-signature get runtimeType() → core::Type*;
 }
-external static abstract method createExternal() → self::External*;
+external static method createExternal() → self::External*;
 static method main() → dynamic
   ;

pkg/front_end/testcases/general/optional.dart.strong.expect

@@ -108,7 +108,7 @@ class InvalidListener extends core::Object {
   abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic;
   abstract member-signature get runtimeType() → core::Type*;
 }
-external static abstract method createExternal() → self::External*;
+external static method createExternal() → self::External*;
 static method main() → dynamic {
   self::Foo* foo = new self::Foo::•();
   dynamic string1 = foo.{self::Foo::method}(1);

pkg/front_end/testcases/general_nnbd_opt_out/micro.dart.weak.expect

@@ -123,8 +123,8 @@ class DynamicReceiver2 extends core::Object {
 static method staticMethod() → dynamic {
   return "sdfg";
 }
-external static abstract method externalStatic() → core::bool*;
-external static abstract method createBar() → self::Bar*;
+external static method externalStatic() → core::bool*;
+external static method createBar() → self::Bar*;
 static method stringArgument(dynamic x) → dynamic {}
 static method intArgument(dynamic x) → dynamic {}
 static method makeDynamicCall(dynamic receiver) → void {

pkg/front_end/testcases/general_nnbd_opt_out/micro.dart.weak.transformed.expect

@@ -123,8 +123,8 @@ class DynamicReceiver2 extends core::Object {
 static method staticMethod() → dynamic {
   return "sdfg";
 }
-external static abstract method externalStatic() → core::bool*;
-external static abstract method createBar() → self::Bar*;
+external static method externalStatic() → core::bool*;
+external static method createBar() → self::Bar*;
 static method stringArgument(dynamic x) → dynamic {}
 static method intArgument(dynamic x) → dynamic {}
 static method makeDynamicCall(dynamic receiver) → void {

pkg/front_end/testcases/general_nnbd_opt_out/optional.dart.weak.expect

@@ -108,7 +108,7 @@ class InvalidListener extends core::Object {
   abstract member-signature method noSuchMethod(core::Invocation* invocation) → dynamic;
   abstract member-signature get runtimeType() → core::Type*;
 }
-external static abstract method createExternal() → self::External*;
+external static method createExternal() → self::External*;
 static method main() → dynamic {
   self::Foo* foo = new self::Foo::•();
   dynamic string1 = foo.{self::Foo::method}(1);

pkg/front_end/testcases/nnbd/abstract_field_errors.dart.outline.expect

@@ -193,22 +193,22 @@ abstract class A extends core::Object {
   abstract set initializedField1(core::int #t2) → void;
   abstract get initializedField2() → core::int;
   abstract set initializedField2(core::int #t3) → void;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t4) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t5) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t4) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t5) → void;
   external get externalLateInstanceField() → core::int;
   external set externalLateInstanceField(core::int #t6) → void;
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   static field core::int staticField;
   static final field core::int finalStaticField;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t7) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t8) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t7) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t8) → void;
 }
 extension Extension on self::A {
   get extensionInstanceField = get self::Extension|extensionInstanceField;

pkg/front_end/testcases/nnbd/abstract_field_errors.dart.strong.expect

@@ -225,22 +225,22 @@ Try removing the field initializer or the 'abstract' keyword from the field decl
   abstract set initializedField1(core::int #t4) → void;
   abstract get initializedField2() → core::int;
   abstract set initializedField2(core::int #t5) → void;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t6) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t7) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t6) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t7) → void;
   external get externalLateInstanceField() → core::int;
   external set externalLateInstanceField(core::int #t8) → void;
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   static field core::int staticField = null;
   static final field core::int finalStaticField = null;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t9) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t10) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t9) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t10) → void;
 }
 extension Extension on self::A {
   get extensionInstanceField = get self::Extension|extensionInstanceField;

pkg/front_end/testcases/nnbd/abstract_field_errors.dart.strong.transformed.expect

@@ -225,22 +225,22 @@ Try removing the field initializer or the 'abstract' keyword from the field decl
   abstract set initializedField1(core::int #t4) → void;
   abstract get initializedField2() → core::int;
   abstract set initializedField2(core::int #t5) → void;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t6) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t7) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t6) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t7) → void;
   external get externalLateInstanceField() → core::int;
   external set externalLateInstanceField(core::int #t8) → void;
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   static field core::int staticField = null;
   static final field core::int finalStaticField = null;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t9) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t10) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t9) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t10) → void;
 }
 extension Extension on self::A {
   get extensionInstanceField = get self::Extension|extensionInstanceField;

pkg/front_end/testcases/nnbd/abstract_field_errors.dart.weak.expect

@@ -225,22 +225,22 @@ Try removing the field initializer or the 'abstract' keyword from the field decl
   abstract set initializedField1(core::int #t4) → void;
   abstract get initializedField2() → core::int;
   abstract set initializedField2(core::int #t5) → void;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t6) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t7) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t6) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t7) → void;
   external get externalLateInstanceField() → core::int;
   external set externalLateInstanceField(core::int #t8) → void;
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   static field core::int staticField = null;
   static final field core::int finalStaticField = null;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t9) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t10) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t9) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t10) → void;
 }
 extension Extension on self::A {
   get extensionInstanceField = get self::Extension|extensionInstanceField;

pkg/front_end/testcases/nnbd/abstract_field_errors.dart.weak.transformed.expect

@@ -225,22 +225,22 @@ Try removing the field initializer or the 'abstract' keyword from the field decl
   abstract set initializedField1(core::int #t4) → void;
   abstract get initializedField2() → core::int;
   abstract set initializedField2(core::int #t5) → void;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t6) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t7) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t6) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t7) → void;
   external get externalLateInstanceField() → core::int;
   external set externalLateInstanceField(core::int #t8) → void;
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   static field core::int staticField = null;
   static final field core::int finalStaticField = null;
-  external abstract get externalInstanceField() → core::int;
-  external abstract set externalInstanceField(core::int #t9) → void;
-  external abstract get externalFinalInstanceField() → core::int;
-  external abstract get externalCovariantInstanceField() → core::num;
-  external abstract set externalCovariantInstanceField(covariant core::num #t10) → void;
+  external get externalInstanceField() → core::int;
+  external set externalInstanceField(core::int #t9) → void;
+  external get externalFinalInstanceField() → core::int;
+  external get externalCovariantInstanceField() → core::num;
+  external set externalCovariantInstanceField(covariant core::num #t10) → void;
 }
 extension Extension on self::A {
   get extensionInstanceField = get self::Extension|extensionInstanceField;

pkg/front_end/testcases/nnbd/platform_definite_assignment/main.dart.outline.expect

@@ -35,6 +35,6 @@ class Class<T extends core::num = core::num> extends core::Object /*hasConstCons
 static method method(core::int a) → core::int
   ;
 @_in::patch
-external static abstract method patchedMethod(core::int a) → void;
+external static method patchedMethod(core::int a) → void;
 static method /* from org-dartlang-testcase:///patch_lib.dart */ _injectedMethod(core::int i) → core::int
   ;

pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.outline.expect

@@ -58,6 +58,6 @@ class Class extends core::Object {
 static method method([core::int i]) → void
   ;
 @_in::patch
-external static abstract method patchedMethod([core::int i]) → void;
+external static method patchedMethod([core::int i]) → void;
 static method /* from org-dartlang-testcase:///patch_lib.dart */ _injectedMethod([core::int i]) → void
   ;

pkg/kernel/lib/verifier.dart

@@ -293,6 +293,9 @@ class VerifyingVisitor extends RecursiveVisitor<void> {
     currentMember = node;
     var oldParent = enterParent(node);
     classTypeParametersAreInScope = !node.isStatic;
+    if (node.isAbstract && node.isExternal) {
+      problem(node, "Procedure cannot be both abstract and external.");
+    }
     node.function.accept(this);
     classTypeParametersAreInScope = false;
     visitList(node.annotations, this);