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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 2008 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.rhino.JSDocInfo;
import com.google.javascript.rhino.JSTypeExpression;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.StaticSourceFile;

/**
 * A simple pass to enforce some invariants about source information.
 *
 * 
 *   All nodes in externs and code have a line number and non-zero length
 *   
All JSTypeExpressions have a source name
 *   
All nodes in a JSTYpeExpression have a source file attached (does not verify lineno or
 *       charno)
 * 
 *
 * This pass does not check the content of the line numbers for things like "being monotonically
 * increasing" because we often insert generated code with out-of-order line numbers. (e.g. imagine
 * inlining a function from a.js into b.js, but having the source information point to a.js)
 */
class SourceInfoCheck implements NodeTraversal.Callback, CompilerPass {

  private static final DiagnosticType MISSING_LINE_INFO =
      DiagnosticType.error(
          "JSC_MISSING_LINE_INFO",
          "No source location information associated with {0}."
              + "\nMost likely a Node has been created without setting the source file"
              + " and line/column location.  Usually this is done using"
              + " Node.srcrefIfMissing and supplying a Node from the source AST.");

  private static final DiagnosticType MISSING_LENGTH =
      DiagnosticType.error(
          "JSC_MISSING_LENGTH",
          "Negative length associated with {0}.\n"
              + "Most likely a Node's source information was set incorrectly at parse time.");

  private static final DiagnosticType MISSING_SOURCE_NAME =
      DiagnosticType.error(
          "JSC_MISSING_SOURCE_NAME",
          "No source name associated with {0}.\n"
              + "Most likely a new type was created without setting the source name.");

  private final AbstractCompiler compiler;
  private boolean requiresLineNumbers = false;

  SourceInfoCheck(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  public void setCheckSubTree(Node root) {
    requiresLineNumbers = true;

    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void process(Node externs, Node root) {
    requiresLineNumbers = false;

    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public boolean shouldTraverse(NodeTraversal unused, Node n, Node parent) {
    // Each JavaScript file is rooted in a script node, so we'll only
    // have line number information inside the script node.
    if (n.isScript()) {
      requiresLineNumbers = true;
    }
    return true;
  }

  @Override
  public void visit(NodeTraversal unused, Node n, Node parent) {
    if (n.isScript()) {
      requiresLineNumbers = false;
    } else if (requiresLineNumbers) {
      if (n.getLineno() == -1) {
        // The tree version of the node is really the best diagnostic
        // info we have to offer here.
        compiler.report(JSError.make(n, MISSING_LINE_INFO, n.toStringTree()));
      } else if (n.getLength() < 0) {
        compiler.report(JSError.make(n, MISSING_LENGTH, n.toStringTree()));
      }
      JSDocInfo info = n.getJSDocInfo();
      if (info != null) {
        checkJSDoc(info);
      }
    }
  }

  /** Verifies that all type nodes have source files (if not an actual length) */
  private void checkJSDoc(JSDocInfo info) {
    for (JSTypeExpression expression : info.getTypeExpressions()) {
      if (expression.getSourceName() == null) {
        compiler.report(
            JSError.make(
                expression.getRoot(), MISSING_SOURCE_NAME, "JSTypeExpression " + expression));
      } else {
        NodeUtil.visitPreOrder(expression.getRoot(), this::checkSourceFile);
      }
    }
  }

  private void checkSourceFile(Node n) {
    StaticSourceFile sourceName = n.getStaticSourceFile();
    if (sourceName == null) {
      compiler.report(JSError.make(n, MISSING_SOURCE_NAME, "type node " + n.toStringTree()));
    }
  }
}