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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.javascript.jscomp;

import com.google.javascript.jscomp.NodeTraversal.Callback;
import com.google.javascript.rhino.Node;

/**
 * Check for errors related to the `super` keyword.
 */
final class CheckSuper implements HotSwapCompilerPass, Callback {
  static final DiagnosticType MISSING_CALL_TO_SUPER =
      DiagnosticType.error("JSC_MISSING_CALL_TO_SUPER", "constructor is missing a call to super()");

  static final DiagnosticType THIS_BEFORE_SUPER =
      DiagnosticType.error("JSC_THIS_BEFORE_SUPER", "cannot access this before calling super()");

  static final DiagnosticType INVALID_SUPER_CALL = DiagnosticType.error(
      "JSC_INVALID_SUPER_CALL",
      "super() not allowed except in the constructor of a subclass");

  static final DiagnosticType INVALID_SUPER_CALL_WITH_SUGGESTION = DiagnosticType.error(
      "JSC_INVALID_SUPER_CALL_WITH_SUGGESTION",
      "super() not allowed here. Did you mean super.{0}?");

  private final AbstractCompiler compiler;

  public CheckSuper(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverseEs6(compiler, root, this);
  }

  @Override
  public void hotSwapScript(Node scriptRoot, Node originalRoot) {
    NodeTraversal.traverseEs6(compiler, scriptRoot, this);
  }

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    if (n.isClass()) {
      return visitClass(t, n);
    }
    return true;
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (n.isSuper()) {
      visitSuper(t, n, parent);
    }
  }

  /**
   * @return Whether to continue traversing this class
   */
  private boolean visitClass(NodeTraversal t, Node n) {
    Node superclass = n.getSecondChild();
    if (superclass.isEmpty()) {
      return true;
    }

    Node constructor =
        NodeUtil.getFirstPropMatchingKey(NodeUtil.getClassMembers(n), "constructor");
    if (constructor == null) {
      return true;
    }

    FindSuper finder = new FindSuper();
    NodeTraversal.traverseEs6(compiler, NodeUtil.getFunctionBody(constructor), finder);

    if (!finder.found) {
      t.report(constructor, MISSING_CALL_TO_SUPER);
      return false;
    }
    return true;
  }

  private void visitSuper(NodeTraversal t, Node n, Node parent) {
    Node classNode = NodeUtil.getEnclosingClass(n);
    if (classNode == null || classNode.getSecondChild().isEmpty()) {
      t.report(n, INVALID_SUPER_CALL);
      return;
    }

    if (parent.isCall()) {
      Node fn = NodeUtil.getEnclosingFunction(parent);
      if (fn == null) {
        t.report(n, INVALID_SUPER_CALL);
        return;
      }

      Node memberDef = fn.getParent();
      if (memberDef.isMemberFunctionDef()) {
        if (memberDef.matchesQualifiedName("constructor")) {
          // No error.
        } else {
          t.report(n, INVALID_SUPER_CALL_WITH_SUGGESTION, memberDef.getString());
        }
      } else {
        t.report(n, INVALID_SUPER_CALL);
      }
    }
  }

  private static final class FindSuper implements Callback {
    boolean found = false;

    @Override
    public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
      // Stop traversal once the super() call is found. Also don't traverse into nested functions
      // since this and super() references may not be applicable within those scopes.
      return !found && !n.isFunction();
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (n.isThis()) {
        t.report(n, THIS_BEFORE_SUPER);
      }
      if (n.isSuper() && parent.isCall()) {
        found = true;
        return;
      }
    }
  }
}