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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.lint;

import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.CompilerPass;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.jscomp.SourceFile;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.StaticSourceFile;
import java.io.IOException;

/**
 * Check for statements that should end with a semicolon according to the Google style guide.
 */
public final class CheckMissingSemicolon extends AbstractPostOrderCallback implements CompilerPass {
  public static final DiagnosticType MISSING_SEMICOLON = DiagnosticType.disabled(
      "JSC_MISSING_SEMICOLON",
      "Missing semicolon");

  private final AbstractCompiler compiler;

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

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

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (!n.isScript() && NodeUtil.isStatement(n) && shouldHaveSemicolon(n)) {
      checkSemicolon(t, n);
    }
  }

  private boolean shouldHaveSemicolon(Node statement) {
    if (statement.isFunction()
        || statement.isClass()
        || statement.isBlock()
        || statement.isLabelName()
        || statement.isModuleBody()
        || (NodeUtil.isControlStructure(statement) && !statement.isDo())) {
      return false;
    }
    if (statement.isExport()) {
      return shouldHaveSemicolon(statement.getFirstChild());
    }
    return true;
  }

  private void checkSemicolon(NodeTraversal t, Node n) {
    StaticSourceFile staticSourceFile = n.getStaticSourceFile();
    if (staticSourceFile instanceof SourceFile) {
      SourceFile sourceFile = (SourceFile) staticSourceFile;

      String code;
      try {
        code = sourceFile.getCode();
      } catch (IOException e) {
        // We can't read the original source file. Just skip this check.
        return;
      }

      int length = n.getLength();
      if (length == 0) {
        // This check needs node lengths to work correctly. If we're not in IDE mode, we don't have
        // that information, so just skip the check.
        return;
      }
      int position = n.getSourceOffset() + length - 1;
      boolean endsWithSemicolon = code.charAt(position) == ';';
      if (!endsWithSemicolon) {
        t.report(n, MISSING_SEMICOLON);
      }
    }
  }
}