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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 2019 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.CodingConvention;
import com.google.javascript.jscomp.CompilerPass;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.JSError;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.jscomp.Var;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;

/**
 * This pass looks for module-level variable declarations that use CONSTANT_CASE, according to the
 * Google style guide, and verifies that they are also annotated @const or are in a const clause.
 *
 * This pass could be extended to check CONSTANT_CASE properties in the future.
 *
 * Non-module-level variables should always use camel case according to the Google style guide.
 * In order to not confuse users, this pass does not warn that they should be @const. (A more
 * correct lint check could warn that non-module-locals should not be constant case.)
 */
public class CheckConstantCaseNames implements NodeTraversal.Callback, CompilerPass {

  public static final DiagnosticType MISSING_CONST_PROPERTY =
      DiagnosticType.disabled(
          "JSC_MISSING_CONST_ON_CONSTANT_CASE",
          "CONSTANT_CASE name \"{0}\" is constant-by-convention, so must be explicitly"
              + " `const` or @const");

  public static final DiagnosticType REASSIGNED_CONSTANT_CASE_NAME =
      DiagnosticType.disabled(
          "JSC_REASSIGNED_CONSTANT_CASE_NAME",
          "CONSTANT_CASE name \"{0}\" is constant-by-convention but is reassigned. "
              + "Use camelCase instead.");

  private final AbstractCompiler compiler;
  private final CodingConvention convention;
  // Maps CONSTANT_CASE module-level names to their initializing NAME node
  private LinkedHashMap invalidNamesPerModule = new LinkedHashMap<>();
  // Subset of variables in `invalidNamesPerModule` that are mutated post-declaration.
  private LinkedHashSet reassignedNames = new LinkedHashSet<>();

  public CheckConstantCaseNames(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.convention = compiler.getCodingConvention();
  }

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

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    // Only need to warn for module-level names, so don't visit other files.
    if (n.isScript()) {
      return n.hasChildren() && n.getFirstChild().isModuleBody();
    }
    return true;
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (n.isModuleBody()) {
      reportWarningsAndClear();
      return;
    }
    switch (n.getToken()) {
      case VAR:
      case LET:
        // Skip CONST as it automatically meets the criteria and only look for module-level vars.
        if (!t.inModuleScope()) {
          return;
        }
        JSDocInfo info = n.getJSDocInfo();
        if (info != null && info.hasConstAnnotation()) {
          break;
        }
        NodeUtil.visitLhsNodesInNode(
            n,
            (name) -> {
              if (convention.isConstant(name.getString())) {
                this.invalidNamesPerModule.put(name.getString(), name);
              }
            });
        break;

      case NAME:
        if (!this.invalidNamesPerModule.containsKey(n.getString())) {
          return;
        }
        if (!NodeUtil.isLValue(n)) {
          return;
        }
        // Verify this name is referring to the actual module-level var and not a local shadow.
        Var v = t.getScope().getVar(n.getString());
        if (v.getScopeRoot().isModuleBody()) {
          this.reassignedNames.add(n.getString());
        }
        break;

      default:
        break;
    }
  }

  private void reportWarningsAndClear() {
    for (Node nameNode : this.invalidNamesPerModule.values()) {
      String name = nameNode.getString();
      if (this.reassignedNames.contains(name)) {
        compiler.report(JSError.make(nameNode, REASSIGNED_CONSTANT_CASE_NAME, name));
      } else {
        compiler.report(JSError.make(nameNode, MISSING_CONST_PROPERTY, name));
      }
    }
    this.invalidNamesPerModule = new LinkedHashMap<>();
    this.reassignedNames = new LinkedHashSet<>();
  }
}