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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 2018 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.ijs;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;

import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.QualifiedName;
import org.jspecify.nullness.Nullable;

/**
 * A callback that calls the abstract method on every "inferrable const". This is a constant
 * declaration for which there is no declared type and an RHS is present. This is useful for giving
 * warnings like the CONSTANT_WITHOUT_EXPLICIT_TYPE diagnostic.
 *
 * As a side effect, this callback also populates the given FileInfo (assumed empty) with all of
 * the declarations found throughout the compilation.
 */
abstract class ProcessConstJsdocCallback extends NodeTraversal.AbstractPostOrderCallback {

  private static final QualifiedName GOOG_DEFINE = QualifiedName.of("goog.define");
  private static final QualifiedName GOOG_PROVIDE = QualifiedName.of("goog.provide");
  private static final QualifiedName GOOG_REQUIRE = QualifiedName.of("goog.require");
  private static final QualifiedName CJS_REQUIRE = QualifiedName.of("require");

  private final FileInfo currentFile;

  ProcessConstJsdocCallback(FileInfo currentFile) {
    this.currentFile = currentFile;
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case CLASS:
        if (NodeUtil.isStatementParent(parent)) {
          currentFile.recordNameDeclaration(n.getFirstChild());
        }
        break;
      case MEMBER_FIELD_DEF:
        if (NodeUtil.getRValueOfLValue(n) != null) {
          processDeclarationWithRhs(t, n);
        }
        currentFile.recordMemberFieldDef(n);
        break;
      case FUNCTION:
        if (NodeUtil.isStatementParent(parent)) {
          currentFile.recordNameDeclaration(n.getFirstChild());
        } else if (ClassUtil.isClassMethod(n) && ClassUtil.hasNamedClass(n)) {
          currentFile.recordMethod(n);
        }
        break;
      case EXPR_RESULT:
        Node expr = n.getFirstChild();
        switch (expr.getToken()) {
          case CALL:
            Node callee = expr.getFirstChild();
            if (GOOG_PROVIDE.matches(callee)) {
              currentFile.markProvided(expr.getLastChild().getString());
            } else if (GOOG_REQUIRE.matches(callee) || CJS_REQUIRE.matches(callee)) {
              currentFile.recordImport(expr.getLastChild().getString());
            } else if (GOOG_DEFINE.matches(callee)) {
              currentFile.recordDefine(expr);
            }
            break;
          case ASSIGN:
            recordDeclaration(t, expr.getFirstChild(), expr.getLastChild());
            break;
          case GETPROP:
            currentFile.recordNameDeclaration(expr);
            break;
          default:
            throw new RuntimeException("Unexpected declaration: " + expr);
        }
        break;
      case VAR:
      case CONST:
      case LET:
        checkState(n.hasOneChild(), n);
        recordDeclaration(t, n.getFirstChild(), n.getFirstChild().getLastChild());
        break;
      case STRING_KEY:
        if (parent.isObjectLit() && n.hasOneChild()) {
          processDeclarationWithRhs(t, n);
          currentFile.recordStringKeyDeclaration(n);
        }
        break;
      default:
        break;
    }
  }

  private void recordDeclaration(NodeTraversal t, Node lhs, @Nullable Node rhs) {
    if (rhs != null
        && rhs.isCall()
        && GOOG_DEFINE.matches(rhs.getFirstChild())
        && lhs.isQualifiedName()) {
      currentFile.recordDefine(rhs);
    } else {
      recordNameDeclaration(lhs, rhs);
      if (!lhs.isDestructuringLhs() && rhs != null) {
        processDeclarationWithRhs(t, lhs);
      }
    }
  }

  private void recordNameDeclaration(Node lhs, @Nullable Node rhs) {
    checkArgument(NodeUtil.isNameDeclaration(lhs.getParent()) || lhs.getParent().isAssign());
    boolean isImport = PotentialDeclaration.isImportRhs(rhs);
    boolean isAlias = PotentialDeclaration.isAliasDeclaration(lhs, rhs);
    NodeUtil.visitLhsNodesInNode(
        lhs.getParent(),
        (name) -> {
          if (isAlias || isImport) {
            currentFile.recordAliasDeclaration(name);
          } else {
            currentFile.recordNameDeclaration(name);
          }
        });
  }

  private void processDeclarationWithRhs(NodeTraversal t, Node lhs) {
    checkArgument(lhs.isQualifiedName() || lhs.isStringKey() || lhs.isMemberFieldDef(), lhs);
    checkState(NodeUtil.getRValueOfLValue(lhs) != null, lhs);
    if (PotentialDeclaration.isConstToBeInferred(lhs)) {
      processConstWithRhs(t, lhs);
    }
  }

  protected abstract void processConstWithRhs(NodeTraversal t, Node lhs);
}