Compute names referenced in a unit.

pkg/analyzer/lib/src/dart/analysis/referenced_names.dart

+// Copyright (c) 2016, 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/ast/visitor.dart';
+
+/**
+ * Compute the set of external names referenced in the [unit].
+ */
+Set<String> computeReferencedNames(CompilationUnit unit) {
+  _ReferencedNamesComputer computer = new _ReferencedNamesComputer();
+  unit.accept(computer);
+  return computer.names;
+}
+
+class _LocalNameScope {

[Brian Wilkerson, 2016/11/18 17:55:51]

Consider renaming (and documenting) the class. It appears that it represents a
general name scope rather than a name scope that only contains local names.

[scheglov, 2016/11/18 18:33:44]

I've added a comment.

+  final _LocalNameScope enclosing;
+  Set<String> names;
+
+  _LocalNameScope(this.enclosing);
+
+  factory _LocalNameScope.forBlock(_LocalNameScope enclosing, Block node) {
+    _LocalNameScope scope = new _LocalNameScope(enclosing);
+    for (Statement statement in node.statements) {
+      if (statement is FunctionDeclarationStatement) {
+        scope.add(statement.functionDeclaration.name.name);
+      } else if (statement is VariableDeclarationStatement) {
+        for (VariableDeclaration variable in statement.variables.variables) {
+          scope.add(variable.name.name);
+        }
+      }
+    }
+    return scope;
+  }
+
+  factory _LocalNameScope.forClass(
+      _LocalNameScope enclosing, ClassDeclaration node) {
+    _LocalNameScope scope = new _LocalNameScope(enclosing);
+    scope.addTypeParameters(node.typeParameters);
+    for (ClassMember member in node.members) {
+      if (member is FieldDeclaration) {
+        for (VariableDeclaration variable in member.fields.variables) {
+          scope.add(variable.name.name);
+        }
+      } else if (member is MethodDeclaration) {
+        scope.add(member.name.name);
+      }
+    }
+    return scope;
+  }
+
+  factory _LocalNameScope.forClassTypeAlias(
+      _LocalNameScope enclosing, ClassTypeAlias node) {
+    _LocalNameScope scope = new _LocalNameScope(enclosing);
+    scope.addTypeParameters(node.typeParameters);
+    return scope;
+  }
+
+  factory _LocalNameScope.forFunction(
+      _LocalNameScope enclosing, FunctionDeclaration node) {
+    _LocalNameScope scope = new _LocalNameScope(enclosing);
+    scope.addTypeParameters(node.functionExpression.typeParameters);
+    scope.addFormalParameters(node.functionExpression.parameters);
+    return scope;
+  }
+
+  factory _LocalNameScope.forFunctionTypeAlias(
+      _LocalNameScope enclosing, FunctionTypeAlias node) {
+    _LocalNameScope scope = new _LocalNameScope(enclosing);
+    scope.addTypeParameters(node.typeParameters);
+    return scope;
+  }
+
+  factory _LocalNameScope.forMethod(
+      _LocalNameScope enclosing, MethodDeclaration node) {
+    _LocalNameScope scope = new _LocalNameScope(enclosing);
+    scope.addTypeParameters(node.typeParameters);
+    scope.addFormalParameters(node.parameters);
+    return scope;
+  }
+
+  void add(String name) {
+    names ??= new Set<String>();
+    names.add(name);
+  }
+
+  void addFormalParameters(FormalParameterList parameterList) {
+    if (parameterList != null) {
+      parameterList.parameters
+          .map((p) => p is NormalFormalParameter ? p.identifier.name : '')
+          .forEach(add);
+    }
+  }
+
+  void addTypeParameters(TypeParameterList typeParameterList) {
+    if (typeParameterList != null) {
+      typeParameterList.typeParameters.map((p) => p.name.name).forEach(add);
+    }
+  }
+
+  bool contains(String name) {
+    if (names != null && names.contains(name)) {
+      return true;
+    }
+    if (enclosing != null) {
+      return enclosing.contains(name);
+    }
+    return false;
+  }
+}
+
+class _ReferencedNamesComputer extends GeneralizingAstVisitor {
+  final Set<String> names = new Set<String>();
+  final Set<String> importPrefixNames = new Set<String>();
+
+  _LocalNameScope localScope = new _LocalNameScope(null);
+  int localLevel = 0;
+
+  @override
+  visitBlock(Block node) {
+    _LocalNameScope outerScope = localScope;
+    try {
+      localScope = new _LocalNameScope.forBlock(localScope, node);
+      super.visitBlock(node);
+    } finally {
+      localScope = outerScope;
+    }
+  }
+
+  @override
+  visitClassDeclaration(ClassDeclaration node) {
+    _LocalNameScope outerScope = localScope;
+    try {
+      localScope = new _LocalNameScope.forClass(localScope, node);
+      super.visitClassDeclaration(node);
+    } finally {
+      localScope = outerScope;
+    }
+  }
+
+  @override
+  visitClassTypeAlias(ClassTypeAlias node) {
+    _LocalNameScope outerScope = localScope;
+    try {
+      localScope = new _LocalNameScope.forClassTypeAlias(localScope, node);
+      super.visitClassTypeAlias(node);
+    } finally {
+      localScope = outerScope;
+    }
+  }
+
+  @override
+  visitComment(Comment node) {
+    try {
+      localLevel++;
+      super.visitComment(node);
+    } finally {
+      localLevel--;
+    }
+  }
+
+  @override
+  visitConstructorName(ConstructorName node) {
+    if (node.parent is! ConstructorDeclaration) {
+      super.visitConstructorName(node);
+    }
+  }
+
+  @override
+  visitFunctionBody(FunctionBody node) {
+    try {
+      localLevel++;
+      super.visitFunctionBody(node);
+    } finally {
+      localLevel--;
+    }
+  }
+
+  @override
+  visitFunctionDeclaration(FunctionDeclaration node) {
+    if (localLevel == 0) {

[Paul Berry, 2016/11/18 17:59:59]

Why do we skip this logic for local functions?  It seems like this would cause
us to do the wrong thing for the following code:

void f() {
  void g(x) {
    print(x);  // "x" references a local parameter, not a global.
  }
}

[scheglov, 2016/11/18 18:33:44]

Acknowledged.
You're right.
I've added the corresponding test.
It turns out we don't need the "localLevel" at all.

+      _LocalNameScope outerScope = localScope;
+      try {
+        localScope = new _LocalNameScope.forFunction(localScope, node);
+        super.visitFunctionDeclaration(node);
+      } finally {
+        localScope = outerScope;
+      }
+    } else {
+      super.visitFunctionDeclaration(node);
+    }
+  }
+
+  @override
+  visitFunctionTypeAlias(FunctionTypeAlias node) {
+    if (localLevel == 0) {

[Paul Berry, 2016/11/18 17:59:59]

Why is this necessary?  I thought function type aliases could only occur at top
level.

[scheglov, 2016/11/18 18:33:44]

Acknowledged.

+      _LocalNameScope outerScope = localScope;
+      try {
+        localScope = new _LocalNameScope.forFunctionTypeAlias(localScope, node);
+        super.visitFunctionTypeAlias(node);
+      } finally {
+        localScope = outerScope;
+      }
+    } else {
+      super.visitFunctionTypeAlias(node);
+    }
+  }
+
+  @override
+  visitImportDirective(ImportDirective node) {
+    if (node.prefix != null) {
+      importPrefixNames.add(node.prefix.name);
+    }
+    super.visitImportDirective(node);
+  }
+
+  @override
+  visitMethodDeclaration(MethodDeclaration node) {
+    _LocalNameScope outerScope = localScope;
+    try {
+      localScope = new _LocalNameScope.forMethod(localScope, node);
+      super.visitMethodDeclaration(node);
+    } finally {
+      localScope = outerScope;
+    }
+  }
+
+  @override
+  visitSimpleIdentifier(SimpleIdentifier node) {
+    // Ignore all declarations.
+    if (node.inDeclarationContext()) {
+      return;
+    }
+    // Ignore class names references from constructors.
+    AstNode parent = node.parent;
+    if (parent is ConstructorDeclaration && parent.returnType == node) {
+      return;
+    }
+    // Prepare name.
+    String name = node.name;
+    // Ignore unqualified names shadowed by local elements.
+    if (!node.isQualified) {
+      if (localScope.contains(name)) {
+        return;

[Paul Berry, 2016/11/18 17:59:59]

What happens if the code looks like this?

void f(x, C g()) {
  print(g().x);
}

I think we should record "x" as a referenced name, because it refers to the "x"
member of class C.  But it looks like we won't record "x" as a referenced name,
because there is a local in scope called "x".

[scheglov, 2016/11/18 18:33:44]

Actually this works.
Local declarations hide only when used unqualified, see "if (!node.isQualified)"
above.
In this example "x" in "g().x" is qualified, so will be added.
I've added the corresponding test.

[Paul Berry, 2016/11/18 19:15:44]

Ah, ok.  I mistakenly thought that "isQualified" just returned true for prefixed
identifiers.  Thanks.

+      }
+      if (importPrefixNames.contains(name)) {
+        return;
+      }
+    }
+    // Do add the name.
+    names.add(name);
+  }
+}