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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 2009 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.common.collect.ImmutableSet;
import com.google.javascript.rhino.Node;

/**
 * A compiler pass that verifies the structure of the AST conforms to a number of invariants.
 * Because this can add a lot of overhead, we only run this in development mode.
 */
class ValidityCheck implements CompilerPass {

  static final DiagnosticType CANNOT_PARSE_GENERATED_CODE =
      DiagnosticType.error(
          "JSC_CANNOT_PARSE_GENERATED_CODE",
          "Internal compiler error. Cannot parse generated code: {0}");

  static final DiagnosticType GENERATED_BAD_CODE =
      DiagnosticType.error(
          "JSC_GENERATED_BAD_CODE",
          "Internal compiler error. Generated bad code."
              + "----------------------------------------\n"
              + "Expected:\n{0}\n"
              + "----------------------------------------\n"
              + "Actual:\n{1}");

  static final DiagnosticType EXTERN_PROPERTIES_CHANGED =
      DiagnosticType.error(
          "JSC_EXTERN_PROPERTIES_CHANGED",
          "Internal compiler error. Extern properties modified from:\n{0}\nto:\n{1}");

  private final AbstractCompiler compiler;
  private final AstValidator astValidator;

  ValidityCheck(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.astValidator = new AstValidator(compiler);
  }

  @Override
  public void process(Node externs, Node root) {
    checkAst(externs, root);
    checkNormalization(externs, root);
    checkVars(externs, root);
    checkExternProperties(externs);
  }

  /** Check that the AST is structurally accurate. */
  private void checkAst(Node externs, Node root) {
    astValidator.validateCodeRoot(externs);
    astValidator.validateCodeRoot(root);
  }

  private void checkVars(Node externs, Node root) {
    if (compiler.getLifeCycleStage().isNormalized()) {
      (new VarCheck(compiler, true)).process(externs, root);
    }
  }

  /** Verifies that the normalization pass does nothing on an already-normalized tree. */
  private void checkNormalization(Node externs, Node root) {
    // Verify nothing has inappropriately denormalize the AST.
    CodeChangeHandler handler = new ForbiddenChange();
    compiler.addChangeHandler(handler);

    // TODO(johnlenz): Change these normalization checks Preconditions and
    // Exceptions into Errors so that it is easier to find the root cause
    // when there are cascading issues.
    if (compiler.getLifeCycleStage().isNormalized()) {
      Normalize.builder(compiler).assertOnChange(true).build().process(externs, root);

      if (compiler.getLifeCycleStage().isNormalizedUnobfuscated()) {
        boolean checkUserDeclarations = true;
        CompilerPass pass = new Normalize.VerifyConstants(compiler, checkUserDeclarations);
        pass.process(externs, root);
      }
    }

    compiler.removeChangeHandler(handler);
  }

  private void checkExternProperties(Node externs) {
    ImmutableSet externProperties = compiler.getExternProperties();
    if (externProperties == null) {
      // GatherExternProperties hasn't run yet. Don't report a violation.
      return;
    }
    new GatherExternProperties(compiler, GatherExternProperties.Mode.CHECK).process(externs, null);
    if (!compiler.getExternProperties().equals(externProperties)) {
      compiler.report(
          JSError.make(
              EXTERN_PROPERTIES_CHANGED,
              externProperties.toString(),
              compiler.getExternProperties().toString()));
      // Throw an exception, so that the infrastructure will tell us which pass violated the check.
      throw new IllegalStateException(
          "Validity Check failed: Extern properties changed from:\n"
              + externProperties
              + "\nto:\n"
              + compiler.getExternProperties());
    }
  }
}