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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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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.base.Preconditions;
import com.google.javascript.jscomp.CodingConvention.AssertionFunctionSpec;
import com.google.javascript.jscomp.NodeTraversal.AbstractScopedCallback;
import com.google.javascript.jscomp.type.ReverseAbstractInterpreter;
import com.google.javascript.rhino.Node;
import java.util.HashMap;
import java.util.Map;

/**
 * A compiler pass to run the type inference analysis.
 *
 */
class TypeInferencePass implements CompilerPass {

  static final DiagnosticType DATAFLOW_ERROR = DiagnosticType.error(
      "JSC_INTERNAL_ERROR_DATAFLOW",
      "non-monotonic data-flow analysis");

  private final AbstractCompiler compiler;
  private final ReverseAbstractInterpreter reverseInterpreter;
  private final TypedScope topScope;
  private final MemoizedScopeCreator scopeCreator;
  private final Map assertionFunctionsMap;

  TypeInferencePass(AbstractCompiler compiler,
      ReverseAbstractInterpreter reverseInterpreter,
      TypedScope topScope, MemoizedScopeCreator scopeCreator) {
    this.compiler = compiler;
    this.reverseInterpreter = reverseInterpreter;
    this.topScope = topScope;
    this.scopeCreator = scopeCreator;

    assertionFunctionsMap = new HashMap<>();
    for (AssertionFunctionSpec assertionFunction :
        compiler.getCodingConvention().getAssertionFunctions()) {
      assertionFunctionsMap.put(assertionFunction.getFunctionName(),
          assertionFunction);
    }
  }

  /**
   * Main entry point for type inference when running over the whole tree.
   *
   * @param externsRoot The root of the externs parse tree.
   * @param jsRoot The root of the input parse tree to be checked.
   */
  @Override
  public void process(Node externsRoot, Node jsRoot) {
    Node externsAndJs = jsRoot.getParent();
    Preconditions.checkState(externsAndJs != null);
    Preconditions.checkState(
        externsRoot == null || externsAndJs.hasChild(externsRoot));

    inferAllScopes(externsAndJs);
  }

  /** Entry point for type inference when running over part of the tree. */
  void inferAllScopes(Node node) {
    // Type analysis happens in two major phases.
    // 1) Finding all the symbols.
    // 2) Propagating all the inferred types.
    //
    // The order of this analysis is non-obvious. In a complete inference
    // system, we may need to backtrack arbitrarily far. But the compile-time
    // costs would be unacceptable.
    //
    // We do one pass where we do typed scope creation for all scopes
    // in pre-order.
    //
    // Then we do a second pass where we do all type inference
    // (type propagation) in pre-order.
    //
    // We use a memoized scope creator so that we never create a scope
    // more than once.
    //
    // This will allow us to handle cases like:
    // var ns = {};
    // (function() { /** JSDoc */ ns.method = function() {}; })();
    // ns.method();
    // In this code, we need to build the symbol table for the inner scope in
    // order to propagate the type of ns.method in the outer scope.
    (new NodeTraversal(
        compiler, new FirstScopeBuildingCallback(), scopeCreator))
        .traverseWithScope(node, topScope);

    for (TypedScope s : scopeCreator.getAllMemoizedScopes()) {
      s.resolveTypes();
    }

    (new NodeTraversal(
        compiler, new SecondScopeBuildingCallback(), scopeCreator))
        .traverseWithScope(node, topScope);
  }

  void inferScope(Node n, TypedScope scope) {
    TypeInference typeInference =
        new TypeInference(
            compiler, computeCfg(n), reverseInterpreter, scope,
            assertionFunctionsMap);
    try {
      typeInference.analyze();

      // Resolve any new type names found during the inference.
      compiler.getTypeRegistry().resolveTypesInScope(scope);

    } catch (DataFlowAnalysis.MaxIterationsExceededException e) {
      compiler.report(JSError.make(n, DATAFLOW_ERROR));
    }
  }

  private static class FirstScopeBuildingCallback extends AbstractScopedCallback {
    @Override
    public void enterScope(NodeTraversal t) {
      t.getTypedScope();
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      // Do nothing
    }
  }

  private class SecondScopeBuildingCallback extends AbstractScopedCallback {
    @Override
    public void enterScope(NodeTraversal t) {
      // Only infer the entry root, rather than the scope root.
      // This ensures that incremental compilation only touches the root
      // that's been swapped out.
      inferScope(t.getCurrentNode(), t.getTypedScope());
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      // Do nothing
    }
  }

  private ControlFlowGraph computeCfg(Node n) {
    ControlFlowAnalysis cfa = new ControlFlowAnalysis(compiler, false, false);
    cfa.process(null, n);
    return cfa.getCfg();
  }
}