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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 2014 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 static com.google.common.base.Preconditions.checkState;

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.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import org.jspecify.nullness.Nullable;

/** Checks for errors related to interfaces. */
public final class CheckInterfaces extends AbstractPostOrderCallback implements CompilerPass {
  // Placeholder class name for error reporting on anonymous classes.
  private static final String ANONYMOUS_CLASSNAME = "";

  public static final DiagnosticType NON_DECLARATION_STATEMENT_IN_INTERFACE =
      DiagnosticType.disabled(
          "JSC_NON_DECLARATION_STATEMENT_IN_INTERFACE",
          "@interface or @record functions should not contain statements other than field"
              + " declarations");

  public static final DiagnosticType MISSING_JSDOC_IN_DECLARATION_STATEMENT =
      DiagnosticType.disabled(
          "JSC_MISSING_JSDOC_IN_DECLARATION_STATEMENT",
          "@interface or @record functions must contain JSDoc for each field declaration.");

  public static final DiagnosticType INTERFACE_CLASS_NONSTATIC_METHOD_NOT_EMPTY =
      DiagnosticType.disabled(
          "JSC_INTERFACE_CLASS_NONSTATIC_METHOD_NOT_EMPTY",
          "interface methods must have an empty body");

  public static final DiagnosticType INTERFACE_CONSTRUCTOR_SHOULD_NOT_TAKE_ARGS =
      DiagnosticType.disabled(
          "JSC_INTERFACE_CONSTRUCTOR_SHOULD_NOT_TAKE_ARGS",
          "Interface constructors should not take any arguments");

  public static final DiagnosticType STATIC_MEMBER_FUNCTION_IN_INTERFACE_CLASS =
      DiagnosticType.disabled(
          "JSC_STATIC_MEMBER_FUNCTION_IN_INTERFACE_CLASS",
          "Interface class should not have static member functions. "
              + "Consider pulling out the static method into a flat name as {0}_{1}");

  public static final DiagnosticType INTERFACE_DEFINED_WITH_EXTENDS =
      DiagnosticType.disabled(
          "JSC_INTERFACE_DEFINED_WITH_EXTENDS",
          "Interface/Record class should use the `@extends` annotation instead of extends"
              + " keyword.");

  private final AbstractCompiler compiler;

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

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

  /** Whether jsDoc is present and has an {@code @interface} or {@code @record} annotation */
  private static boolean isInterface(JSDocInfo jsDoc) {
    return jsDoc != null && jsDoc.isInterface();
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case FUNCTION:
        {
          JSDocInfo jsdoc = NodeUtil.getBestJSDocInfo(n);
          if (isInterface(jsdoc)) {
            checkInterfaceConstructorArgs(t, n);
            checkConstructorBlock(t, n);
          }
          break;
        }
      case CLASS:
        {
          JSDocInfo jsdoc = NodeUtil.getBestJSDocInfo(n);
          if (isInterface(jsdoc)) {
            if (n.getSecondChild() != null && n.getSecondChild().isName()) {
              t.report(n, INTERFACE_DEFINED_WITH_EXTENDS);
            }
            Node ctorDef = NodeUtil.getEs6ClassConstructorMemberFunctionDef(n);
            if (ctorDef != null) {
              Node ctor = ctorDef.getFirstChild();
              checkInterfaceConstructorArgs(t, ctor);
              checkConstructorBlock(t, ctor);
            }
            checkClassMethods(t, n, ctorDef);
          }
          break;
        }
      default:
        return;
    }
  }

  private static void checkInterfaceConstructorArgs(NodeTraversal t, Node funcNode) {
    Node args = funcNode.getSecondChild();
    if (args.hasChildren()) {
      t.report(args.getFirstChild(), INTERFACE_CONSTRUCTOR_SHOULD_NOT_TAKE_ARGS);
    }
  }

  // Non-static class methods must be empty for `@record` and `@interface` as per the style guide.
  private static void checkClassMethods(NodeTraversal t, Node classNode, @Nullable Node ctorDef) {
    Node classMembers = classNode.getLastChild();
    checkState(classMembers.isClassMembers(), classMembers);
    for (Node memberFuncDef = classMembers.getFirstChild();
        memberFuncDef != null;
        memberFuncDef = memberFuncDef.getNext()) {
      if (memberFuncDef.equals(ctorDef)) {
        continue; // constructor was already checked; don't check here.
      }
      if (memberFuncDef.isStaticMember()) {
        // `static foo() {...}`
        String className = NodeUtil.getName(classNode);
        if (className == null) {
          className = ANONYMOUS_CLASSNAME;
        }
        String funcName = memberFuncDef.getString();
        t.report(memberFuncDef, STATIC_MEMBER_FUNCTION_IN_INTERFACE_CLASS, className, funcName);
      } else {
        Node block = memberFuncDef.getLastChild().getLastChild();
        if (block.hasChildren()) {
          t.report(block.getFirstChild(), INTERFACE_CLASS_NONSTATIC_METHOD_NOT_EMPTY);
        }
      }
    }
  }

  // `@record` constructors can be non-empty, check that only field declarations exist in them.
  private static void checkConstructorBlock(NodeTraversal t, Node funcNode) {
    Node block = funcNode.getLastChild();
    if (!block.hasChildren()) {
      return;
    }

    for (Node stmt = block.getFirstChild(); stmt != null; stmt = stmt.getNext()) {
      if (!isThisPropAccess(stmt)) {
        // Only field declarations are expected inside @record and @interface.
        t.report(stmt, NON_DECLARATION_STATEMENT_IN_INTERFACE);
        break;
      } else if (stmt.getFirstChild().getJSDocInfo() == null) {
        // A field declaration that's missing a JSDoc.
        t.report(stmt, MISSING_JSDOC_IN_DECLARATION_STATEMENT);
        break;
      }
    }
  }

  private static boolean isThisPropAccess(Node stmt) {
    return stmt.isExprResult()
        && stmt.getFirstChild().isGetProp()
        && stmt.getFirstFirstChild().isThis();
  }
}