Detach nodes referenced by elements from original units.

This is a necessary step to keep linking elements without loading
from bytes.

Change-Id: I7bc8bdc0b10e178ab46d15e288a76eb3d732891f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/202160
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/analyzer/lib/src/dart/ast/ast.dart

@@ -763,6 +763,10 @@ abstract class AstNodeImpl implements AstNode {
     return root;
   }
 
+  void detachFromParent() {
+    _parent = null;
+  }
+
   @override
   Token? findPrevious(Token target) =>
       util.findPrevious(beginToken, target) ?? parent?.findPrevious(target);

pkg/analyzer/lib/src/summary2/detach_nodes.dart

@@ -0,0 +1,79 @@
+// Copyright (c) 2021, 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.
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/visitor.dart';
+import 'package:analyzer/src/dart/ast/ast.dart';
+import 'package:analyzer/src/dart/element/element.dart';
+
+/// Elements have references to AST nodes, for example initializers of constant
+/// variables. These nodes are attached to the whole compilation unit, and
+/// the whole token stream for the file. We don't want all this data after
+/// linking. So, we need to detach these nodes.
+void detachElementsFromNodes(LibraryElementImpl element) {
+  element.accept(_Visitor());
+}
+
+class _Visitor extends GeneralizingElementVisitor<void> {
+  @override
+  void visitClassElement(ClassElement element) {
+    if (element is ClassElementImpl) {
+      element.mixinInferenceCallback = null;
+    }
+    super.visitClassElement(element);
+  }
+
+  @override
+  void visitConstructorElement(ConstructorElement element) {
+    if (element is ConstructorElementImpl) {
+      // Make a copy, so that it is not a NodeList.
+      var initializers = element.constantInitializers.toList();
+      initializers.forEach(_detachNode);
+      element.constantInitializers = initializers;
+    }
+    super.visitConstructorElement(element);
+  }
+
+  @override
+  void visitElement(Element element) {
+    for (var elementAnnotation in element.metadata) {
+      _detachNode((elementAnnotation as ElementAnnotationImpl).annotationAst);
+    }
+    super.visitElement(element);
+  }
+
+  @override
+  void visitParameterElement(ParameterElement element) {
+    _detachConstVariable(element);
+    super.visitParameterElement(element);
+  }
+
+  @override
+  void visitPropertyInducingElement(PropertyInducingElement element) {
+    if (element is PropertyInducingElementImpl) {
+      element.typeInference = null;
+    }
+    _detachConstVariable(element);
+  }
+
+  void _detachConstVariable(Element element) {
+    if (element is ConstVariableElement) {
+      var initializer = element.constantInitializer;
+      if (initializer is ExpressionImpl) {
+        _detachNode(initializer);
+        ConstantContextForExpressionImpl(initializer);
+      }
+    }
+  }
+
+  void _detachNode(AstNode? node) {
+    if (node is AstNodeImpl) {
+      node.detachFromParent();
+      // Also detach from the token stream.
+      node.beginToken.previous = null;
+      node.endToken.next = null;
+    }
+  }
+}

pkg/analyzer/lib/src/summary2/link.dart

@@ -13,6 +13,7 @@ import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/summary2/bundle_writer.dart';
+import 'package:analyzer/src/summary2/detach_nodes.dart';
 import 'package:analyzer/src/summary2/library_builder.dart';
 import 'package:analyzer/src/summary2/linked_element_factory.dart';
 import 'package:analyzer/src/summary2/reference.dart';
@@ -25,6 +26,8 @@ import 'package:analyzer/src/summary2/variance_builder.dart';
 var timerLinkingLinkingBundle = Stopwatch();
 var timerLinkingRemoveBundle = Stopwatch();
 
+/// Note that AST units and tokens of [inputLibraries] will be damaged.
+///
 /// TODO(scheglov) deprecate `withInformative`.
 LinkResult link(
   LinkedElementFactory elementFactory,
@@ -104,6 +107,7 @@ class Linker {
     _resolveDefaultValues();
     _resolveMetadata();
     _collectMixinSuperInvokedNames();
+    _detachNodes();
   }
 
   void _collectMixinSuperInvokedNames() {
@@ -178,6 +182,12 @@ class Linker {
     inheritance = InheritanceManager3();
   }
 
+  void _detachNodes() {
+    for (var builder in builders.values) {
+      detachElementsFromNodes(builder.element);
+    }
+  }
+
   void _performTopLevelInference() {
     TopLevelInference(this).infer();
   }