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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.
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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.parsing;

import com.google.common.base.Ascii;
import com.google.common.base.Preconditions;
import com.google.javascript.jscomp.parsing.Config.LanguageMode;
import com.google.javascript.jscomp.parsing.ParserRunner.ParseResult;
import com.google.javascript.rhino.ErrorReporter;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.SimpleErrorReporter;
import com.google.javascript.rhino.StaticSourceFile;
import java.util.HashSet;

/**
 * A parser for the type transformation expressions (TTL-Exp) as in
 * {@code @template T := TTL-Exp =:}
 *
 */
public final class TypeTransformationParser {

  private final String typeTransformationString;
  private Node typeTransformationAst;
  private final StaticSourceFile sourceFile;
  private final ErrorReporter errorReporter;
  private final int templateLineno;
  private final int templateCharno;

  private static final int VAR_ARGS = Integer.MAX_VALUE;

  /** The classification of the keywords */
  public static enum OperationKind {
    TYPE_CONSTRUCTOR,
    OPERATION,
    STRING_PREDICATE,
    TYPE_PREDICATE,
    TYPEVAR_PREDICATE
  }

  /** Keywords of the type transformation language */
  public static enum Keywords {
    ALL("all", 0, 0, OperationKind.TYPE_CONSTRUCTOR),
    COND("cond", 3, 3, OperationKind.OPERATION),
    EQ("eq", 2, 2, OperationKind.TYPE_PREDICATE),
    ISCTOR("isCtor", 1, 1, OperationKind.TYPE_PREDICATE),
    ISDEFINED("isDefined", 1, 1, OperationKind.TYPEVAR_PREDICATE),
    ISRECORD("isRecord", 1, 1, OperationKind.TYPE_PREDICATE),
    ISTEMPLATIZED("isTemplatized", 1, 1, OperationKind.TYPE_PREDICATE),
    ISUNKNOWN("isUnknown", 1, 1, OperationKind.TYPE_PREDICATE),
    INSTANCEOF("instanceOf", 1, 1, OperationKind.OPERATION),
    MAPUNION("mapunion", 2, 2, OperationKind.OPERATION),
    MAPRECORD("maprecord", 2, 2, OperationKind.OPERATION),
    NONE("none", 0, 0, OperationKind.TYPE_CONSTRUCTOR),
    PRINTTYPE("printType", 2, 2, OperationKind.OPERATION),
    PROPTYPE("propType", 2, 2, OperationKind.OPERATION),
    RAWTYPEOF("rawTypeOf", 1, 1, OperationKind.TYPE_CONSTRUCTOR),
    SUB("sub", 2, 2, OperationKind.TYPE_PREDICATE),
    STREQ("streq", 2, 2, OperationKind.STRING_PREDICATE),
    RECORD("record", 1, VAR_ARGS, OperationKind.TYPE_CONSTRUCTOR),
    TEMPLATETYPEOF("templateTypeOf", 2, 2, OperationKind.TYPE_CONSTRUCTOR),
    TYPE("type", 2, VAR_ARGS, OperationKind.TYPE_CONSTRUCTOR),
    TYPEEXPR("typeExpr", 1, 1, OperationKind.TYPE_CONSTRUCTOR),
    TYPEOFVAR("typeOfVar", 1, 1, OperationKind.OPERATION),
    UNION("union", 2, VAR_ARGS, OperationKind.TYPE_CONSTRUCTOR),
    UNKNOWN("unknown", 0, 0, OperationKind.TYPE_CONSTRUCTOR);

    public final String name;
    public final int minParamCount;
    public final int maxParamCount;
    public final OperationKind kind;

    Keywords(String name, int minParamCount, int maxParamCount,
        OperationKind kind) {
      this.name = name;
      this.minParamCount = minParamCount;
      this.maxParamCount = maxParamCount;
      this.kind = kind;
    }
  }

  public TypeTransformationParser(String typeTransformationString,
      StaticSourceFile sourceFile, ErrorReporter errorReporter,
      int templateLineno, int templateCharno) {
    this.typeTransformationString = typeTransformationString;
    this.sourceFile = sourceFile;
    this.errorReporter = errorReporter;
    this.templateLineno = templateLineno;
    this.templateCharno = templateCharno;
  }

  public Node getTypeTransformationAst() {
    return typeTransformationAst;
  }

  private void addNewWarning(String messageId, String messageArg, Node nodeWarning) {
    // TODO(lpino): Use the exact lineno and charno, it is currently using
    // the lineno and charno of the parent @template
    // TODO(lpino): Use only constants as parameters of this method
    errorReporter.warning(
        "Bad type annotation. "
            + SimpleErrorReporter.getMessage1(messageId, messageArg),
            sourceFile.getName(),
            templateLineno,
            templateCharno);
  }

  private Keywords nameToKeyword(String s) {
    return Keywords.valueOf(Ascii.toUpperCase(s));
  }

  private boolean isValidKeyword(String name) {
    for (Keywords k : Keywords.values()) {
      if (k.name.equals(name)) {
        return true;
      }
    }
    return false;
  }

  private boolean isOperationKind(String name, OperationKind kind) {
    return isValidKeyword(name) && nameToKeyword(name).kind == kind;
  }

  private boolean isValidStringPredicate(String name) {
    return isOperationKind(name, OperationKind.STRING_PREDICATE);
  }

  private boolean isValidTypePredicate(String name) {
    return isOperationKind(name, OperationKind.TYPE_PREDICATE);
  }

  private boolean isValidTypevarPredicate(String name) {
    return isOperationKind(name, OperationKind.TYPEVAR_PREDICATE);
  }

  private boolean isBooleanOperation(Node n) {
    return n.isAnd() || n.isOr() || n.isNot();
  }

  private boolean isValidPredicate(String name) {
    return isValidStringPredicate(name)
        || isValidTypePredicate(name)
        || isValidTypevarPredicate(name);
  }

  private int getFunctionParamCount(Node n) {
    Preconditions.checkArgument(n.isFunction(),
        "Expected a function node, found %s", n);
    return n.getSecondChild().getChildCount();
  }

  private Node getFunctionBody(Node n) {
    Preconditions.checkArgument(n.isFunction(),
        "Expected a function node, found %s", n);
    return n.getChildAtIndex(2);
  }

  private String getCallName(Node n) {
    Preconditions.checkArgument(n.isCall(),
        "Expected a call node, found %s", n);
    return n.getFirstChild().getString();
  }

  private Node getCallArgument(Node n, int i) {
    Preconditions.checkArgument(n.isCall(),
        "Expected a call node, found %s", n);
    return n.getChildAtIndex(i + 1);
  }

  private int getCallParamCount(Node n) {
    Preconditions.checkArgument(n.isCall(),
        "Expected a call node, found %s", n);
    return n.getChildCount() - 1;
  }

  private boolean isTypeVar(Node n) {
    return n.isName();
  }

  private boolean isTypeName(Node n) {
    return n.isString();
  }

  private boolean isOperation(Node n) {
    return n.isCall();
  }

  /**
   * A valid expression is either:
   * - NAME for a type variable
   * - STRING for a type name
   * - CALL for the other expressions
   */
  private boolean isValidExpression(Node e) {
    return isTypeVar(e) || isTypeName(e) || isOperation(e);
  }

  private void warnInvalid(String msg, Node e) {
    addNewWarning("msg.jsdoc.typetransformation.invalid", msg, e);
  }

  private void warnInvalidExpression(String msg, Node e) {
    addNewWarning("msg.jsdoc.typetransformation.invalid.expression", msg, e);
  }

  private void warnMissingParam(String msg, Node e) {
    addNewWarning("msg.jsdoc.typetransformation.missing.param", msg, e);
  }

  private void warnExtraParam(String msg, Node e) {
    addNewWarning("msg.jsdoc.typetransformation.extra.param", msg, e);
  }

  private void warnInvalidInside(String msg, Node e) {
    addNewWarning("msg.jsdoc.typetransformation.invalid.inside", msg, e);
  }

  private boolean checkParameterCount(Node expr, Keywords keyword) {
    int paramCount = getCallParamCount(expr);
    if (paramCount < keyword.minParamCount) {
      warnMissingParam(keyword.name, expr);
      return false;
    }
    if (paramCount > keyword.maxParamCount) {
      warnExtraParam(keyword.name, expr);
      return false;
    }
    return true;
  }

  /**
   * Takes a type transformation expression, transforms it to an AST using
   * the ParserRunner of the JSCompiler and then verifies that it is a valid
   * AST.
   * @return true if the parsing was successful otherwise it returns false and
   * at least one warning is reported
   */
  public boolean parseTypeTransformation() {
    Config config =
        new Config(
            new HashSet(),
            new HashSet(),
            LanguageMode.ECMASCRIPT6,
            Config.StrictMode.SLOPPY);
    // TODO(lpino): ParserRunner reports errors if the expression is not
    // ES6 valid. We need to abort the validation of the type transformation
    // whenever an error is reported.
    ParseResult result = ParserRunner.parse(
        sourceFile, typeTransformationString, config, errorReporter);
    Node ast = result.ast;
    // Check that the expression is a script with an expression result
    if (!ast.isScript() || !ast.getFirstChild().isExprResult()) {
      warnInvalidExpression("type transformation", ast);
      return false;
    }

    Node expr = ast.getFirstFirstChild();
    // The AST of the type transformation must correspond to a valid expression
    if (!validTypeTransformationExpression(expr)) {
      // No need to add a new warning because the validation does it
      return false;
    }
    fixLineNumbers(expr);
    // Store the result if the AST is valid
    typeTransformationAst = expr;
    return true;
  }

  private void fixLineNumbers(Node expr) {
    // TODO(tbreisacher): Also fix column numbers.
    expr.setLineno(expr.getLineno() + templateLineno);
    for (Node child : expr.children()) {
      fixLineNumbers(child);
    }
  }

  /**
   * A template type expression must be of the form type(typename, TTLExp,...)
   * or type(typevar, TTLExp...)
   */
  private boolean validTemplateTypeExpression(Node expr) {
    // The expression must have at least three children the type keyword,
    // a type name (or type variable) and a type expression
    if (!checkParameterCount(expr, Keywords.TYPE)) {
      return false;
    }
    int paramCount = getCallParamCount(expr);
    // The first parameter must be a type variable or a type name
    Node firstParam = getCallArgument(expr, 0);
    if (!isTypeVar(firstParam) && !isTypeName(firstParam)) {
      warnInvalid("type name or type variable", expr);
      warnInvalidInside("template type operation", expr);
      return false;
    }
    // The rest of the parameters must be valid type expressions
    for (int i = 1; i < paramCount; i++) {
      if (!validTypeTransformationExpression(getCallArgument(expr, i))) {
        warnInvalidInside("template type operation", expr);
        return false;
      }
    }
    return true;
  }

  /**
   * A Union type expression must be a valid type variable or
   * a union(TTLExp, TTLExp, ...)
   */
  private boolean validUnionTypeExpression(Node expr) {
    // The expression must have at least three children: The union keyword and
    // two type expressions
    if (!checkParameterCount(expr, Keywords.UNION)) {
      return false;
    }
    int paramCount = getCallParamCount(expr);
    // Check if each of the members of the union is a valid type expression
    for (int i = 0; i < paramCount; i++) {
      if (!validTypeTransformationExpression(getCallArgument(expr, i))) {
        warnInvalidInside("union type", expr);
        return false;
      }
    }
    return true;
  }

  /**
   * A none type expression must be of the form: none()
   */
  private boolean validNoneTypeExpression(Node expr) {
    // The expression must have no children
    return checkParameterCount(expr, Keywords.NONE);
  }

  /**
   * An all type expression must be of the form: all()
   */
  private boolean validAllTypeExpression(Node expr) {
    // The expression must have no children
    return checkParameterCount(expr, Keywords.ALL);
  }

  /**
   * An unknown type expression must be of the form: unknown()
   */
  private boolean validUnknownTypeExpression(Node expr) {
    // The expression must have no children
    return checkParameterCount(expr, Keywords.UNKNOWN);
  }

  /**
   * A raw type expression must be of the form rawTypeOf(TTLExp)
   */
  private boolean validRawTypeOfTypeExpression(Node expr) {
    // The expression must have two children. The rawTypeOf keyword and the
    // parameter
    if (!checkParameterCount(expr, Keywords.RAWTYPEOF)) {
      return false;
    }
    // The parameter must be a valid type expression
    if (!validTypeTransformationExpression(getCallArgument(expr, 0))) {
      warnInvalidInside(Keywords.RAWTYPEOF.name, expr);
      return false;
    }
    return true;
  }

  /**
   * A template type of expression must be of the form
   * templateTypeOf(TTLExp, index)
   */
  private boolean validTemplateTypeOfExpression(Node expr) {
    // The expression must have three children. The templateTypeOf keyword, a
    // templatized type and an index
    if (!checkParameterCount(expr, Keywords.TEMPLATETYPEOF)) {
      return false;
    }
    // The parameter must be a valid type expression
    if (!validTypeTransformationExpression(getCallArgument(expr, 0))) {
      warnInvalidInside(Keywords.TEMPLATETYPEOF.name, expr);
      return false;
    }
    if (!getCallArgument(expr, 1).isNumber()) {
      warnInvalid("index", expr);
      warnInvalidInside(Keywords.TEMPLATETYPEOF.name, expr);
      return false;
    }
    double index = getCallArgument(expr, 1).getDouble();
    if (index < 0 || index % 1 != 0) {
      warnInvalid("index", expr);
      warnInvalidInside(Keywords.TEMPLATETYPEOF.name, expr);
      return false;
    }
    return true;
  }

  /**
   * A record must be a valid type transformation expression or a node of the form:
   * {prop:TTLExp, prop:TTLExp, ...}
   * Notice that the values are mandatory and they must be valid type
   * transformation expressions
   */
  private boolean validRecordParam(Node expr) {
    if (expr.isObjectLit()) {
      // Each value of a property must be a valid expression
      for (Node prop : expr.children()) {
        if (!prop.hasChildren()) {
          warnInvalid("property, missing type", prop);
          return false;
        } else if (!validTypeTransformationExpression(prop.getFirstChild())) {
          return false;
        }
      }
    } else if (!validTypeTransformationExpression(expr)) {
      return false;
    }
    return true;
  }

  /**
   * A record type expression must be of the form:
   * record(RecordExp, RecordExp, ...)
   */
  private boolean validRecordTypeExpression(Node expr) {
    // The expression must have at least two children. The record keyword and
    // a record expression
    if (!checkParameterCount(expr, Keywords.RECORD)) {
      return false;
    }
    // Each child must be a valid record
    for (int i = 0; i < getCallParamCount(expr); i++) {
      if (!validRecordParam(getCallArgument(expr, i))) {
        warnInvalidInside(Keywords.RECORD.name, expr);
        return false;
      }
    }
    return true;
  }

  private boolean validNativeTypeExpr(Node expr) {
    // The expression must have two children:
    // - The typeExpr keyword
    // - A string
    if (!checkParameterCount(expr, Keywords.TYPEEXPR)) {
      return false;
    }
    Node typeString = getCallArgument(expr, 0);
    if (!typeString.isString()) {
      warnInvalidExpression("native type", expr);
      warnInvalidInside(Keywords.TYPEEXPR.name, expr);
      return false;
    }
    Node typeExpr = JsDocInfoParser.parseTypeString(typeString.getString());
    typeString.detach();
    expr.addChildToBack(typeExpr);
    return true;
  }

  /**
   * A TTL type expression must be a union type, a template type, a record type
   * or any of the type predicates (none, rawTypeOf, templateTypeOf).
   */
  private boolean validTypeExpression(Node expr) {
    String name = getCallName(expr);
    Keywords keyword = nameToKeyword(name);
    switch (keyword) {
      case TYPE:
        return validTemplateTypeExpression(expr);
      case UNION:
        return validUnionTypeExpression(expr);
      case NONE:
        return validNoneTypeExpression(expr);
      case ALL:
        return validAllTypeExpression(expr);
      case UNKNOWN:
        return validUnknownTypeExpression(expr);
      case RAWTYPEOF:
        return validRawTypeOfTypeExpression(expr);
      case TEMPLATETYPEOF:
        return validTemplateTypeOfExpression(expr);
      case RECORD:
        return validRecordTypeExpression(expr);
      case TYPEEXPR:
        return validNativeTypeExpr(expr);
      default:
        throw new IllegalStateException("Invalid type expression");
    }
  }

  private boolean validTypePredicate(Node expr, int paramCount) {
    // All the types must be valid type expressions
    for (int i = 0; i < paramCount; i++) {
      if (!validTypeTransformationExpression(getCallArgument(expr, i))) {
        warnInvalidInside("boolean", expr);
        return false;
      }
    }
    return true;
  }

  private boolean isValidStringParam(Node expr) {
    if (!expr.isName() && !expr.isString()) {
      warnInvalid("string", expr);
      return false;
    }
    if (expr.getString().isEmpty()) {
      warnInvalid("string parameter", expr);
      return false;
    }
    return true;
  }

  private boolean validStringPredicate(Node expr, int paramCount) {
    // Each parameter must be valid string parameter
    for (int i = 0; i < paramCount; i++) {
      if (!isValidStringParam(getCallArgument(expr, i))) {
        warnInvalidInside("boolean", expr);
        return false;
      }
    }
    return true;
  }

  private boolean validTypevarParam(Node expr) {
    if (!isTypeVar(expr)) {
      warnInvalid("name", expr);
      return false;
    }
    return true;
  }

  private boolean validTypevarPredicate(Node expr, int paramCount) {
    // Each parameter must be valid string parameter
    for (int i = 0; i < paramCount; i++) {
      if (!validTypevarParam(getCallArgument(expr, i))) {
        warnInvalidInside("boolean", expr);
        return false;
      }
    }
    return true;
  }

  private boolean validBooleanOperation(Node expr) {
    boolean valid;
    if (expr.isNot()) {
      valid = validBooleanExpression(expr.getFirstChild());
    } else {
      valid = validBooleanExpression(expr.getFirstChild())
          && validBooleanExpression(expr.getSecondChild());
    }
    if (!valid) {
      warnInvalidInside("boolean", expr);
      return false;
    }
    return true;
  }

  /**
   * A boolean expression must be a boolean predicate or a boolean
   * type predicate
   */
  private boolean validBooleanExpression(Node expr) {
    if (isBooleanOperation(expr)) {
      return validBooleanOperation(expr);
    }

    if (!isOperation(expr)) {
      warnInvalidExpression("boolean", expr);
      return false;
    }
    if (!isValidPredicate(getCallName(expr))) {
      warnInvalid("boolean predicate", expr);
      return false;
    }
    Keywords keyword = nameToKeyword(getCallName(expr));
    if (!checkParameterCount(expr, keyword)) {
      return false;
    }
    switch (keyword.kind) {
      case TYPE_PREDICATE:
        return validTypePredicate(expr, getCallParamCount(expr));
      case STRING_PREDICATE:
        return validStringPredicate(expr, getCallParamCount(expr));
      case TYPEVAR_PREDICATE:
        return validTypevarPredicate(expr, getCallParamCount(expr));
      default:
        throw new IllegalStateException("Invalid boolean expression");
    }
  }

  /**
   * A conditional type transformation expression must be of the
   * form cond(BoolExp, TTLExp, TTLExp)
   */
  private boolean validConditionalExpression(Node expr) {
    // The expression must have four children:
    // - The cond keyword
    // - A boolean expression
    // - A type transformation expression with the 'if' branch
    // - A type transformation expression with the 'else' branch
    if (!checkParameterCount(expr, Keywords.COND)) {
      return false;
    }
    // Check for the validity of the boolean and the expressions
    if (!validBooleanExpression(getCallArgument(expr, 0))) {
      warnInvalidInside("conditional", expr);
      return false;
    }
    if (!validTypeTransformationExpression(getCallArgument(expr, 1))) {
      warnInvalidInside("conditional", expr);
      return false;
    }
    if (!validTypeTransformationExpression(getCallArgument(expr, 2))) {
      warnInvalidInside("conditional", expr);
      return false;
    }
    return true;
  }

  /**
   * A mapunion type transformation expression must be of the form
   * mapunion(TTLExp, (typevar) => TTLExp).
   */
  private boolean validMapunionExpression(Node expr) {
    // The expression must have four children:
    // - The mapunion keyword
    // - A union type expression
    // - A map function
    if (!checkParameterCount(expr, Keywords.MAPUNION)) {
      return false;
    }
    // The second child must be a valid union type expression
    if (!validTypeTransformationExpression(getCallArgument(expr, 0))) {
      warnInvalidInside(Keywords.MAPUNION.name, getCallArgument(expr, 0));
      return false;
    }
    // The third child must be a function
    if (!getCallArgument(expr, 1).isFunction()) {
      warnInvalid("map function", getCallArgument(expr, 1));
      warnInvalidInside(Keywords.MAPUNION.name, getCallArgument(expr, 1));
      return false;
    }
    Node mapFn = getCallArgument(expr, 1);
    // The map function must have only one parameter
    int mapFnParamCount = getFunctionParamCount(mapFn);
    if (mapFnParamCount < 1) {
      warnMissingParam("map function", mapFn);
      warnInvalidInside(Keywords.MAPUNION.name, getCallArgument(expr, 1));
      return false;
    }
    if (mapFnParamCount > 1) {
      warnExtraParam("map function", mapFn);
      warnInvalidInside(Keywords.MAPUNION.name, getCallArgument(expr, 1));
      return false;
    }
    // The body must be a valid type transformation expression
    Node mapFnBody = getFunctionBody(mapFn);
    if (!validTypeTransformationExpression(mapFnBody)) {
      warnInvalidInside("map function body", mapFnBody);
      return false;
    }
    return true;
  }

  /**
   * A maprecord type transformation expression must be of the form
   * maprecord(TTLExp, (typevar, typevar) => TTLExp).
   */
  private boolean validMaprecordExpression(Node expr) {
    // The expression must have four children:
    // - The maprecord keyword
    // - A type expression
    // - A map function
    if (!checkParameterCount(expr, Keywords.MAPRECORD)) {
      return false;
    }
    // The second child must be a valid expression
    if (!validTypeTransformationExpression(getCallArgument(expr, 0))) {
      warnInvalidInside(Keywords.MAPRECORD.name, getCallArgument(expr, 0));
      return false;
    }
    // The third child must be a function
    if (!getCallArgument(expr, 1).isFunction()) {
      warnInvalid("map function", getCallArgument(expr, 1));
      warnInvalidInside(Keywords.MAPRECORD.name, getCallArgument(expr, 1));
      return false;
    }
    Node mapFn = getCallArgument(expr, 1);
    // The map function must have exactly two parameters
    int mapFnParamCount = getFunctionParamCount(mapFn);
    if (mapFnParamCount < 2) {
      warnMissingParam("map function", mapFn);
      warnInvalidInside(Keywords.MAPRECORD.name, getCallArgument(expr, 1));
      return false;
    }
    if (mapFnParamCount > 2) {
      warnExtraParam("map function", mapFn);
      warnInvalidInside(Keywords.MAPRECORD.name, getCallArgument(expr, 1));
      return false;
    }
    // The body must be a valid type transformation expression
    Node mapFnBody = getFunctionBody(mapFn);
    if (!validTypeTransformationExpression(mapFnBody)) {
      warnInvalidInside("map function body", mapFnBody);
      return false;
    }
    return true;
  }

  /**
   * A typeOfVar expression must be of the form typeOfVar('name')
   */
  private boolean validTypeOfVarExpression(Node expr) {
 // The expression must have two children:
    // - The typeOfVar keyword
    // - A string
    if (!checkParameterCount(expr, Keywords.TYPEOFVAR)) {
      return false;
    }
    if (!getCallArgument(expr, 0).isString()) {
      warnInvalid("name", expr);
      warnInvalidInside(Keywords.TYPEOFVAR.name, expr);
      return false;
    }
    return true;
  }

  /**
   * A typeOfVar expression must be of the form instanceOf('name')
   */
  private boolean validInstanceOfExpression(Node expr) {
    // The expression must have two children:
    // - The instanceOf keyword
    // - A string
    if (!checkParameterCount(expr, Keywords.INSTANCEOF)) {
      return false;
    }
    if (!validTypeTransformationExpression(getCallArgument(expr, 0))) {
      warnInvalidInside(Keywords.INSTANCEOF.name, expr);
      return false;
    }
    return true;
  }

  private boolean validPrintTypeExpression(Node expr) {
    // The expression must have three children. The printType keyword, a
    // message and a type transformation expression
    if (!checkParameterCount(expr, Keywords.PRINTTYPE)) {
      return false;
    }
    if (!getCallArgument(expr, 0).isString()) {
      warnInvalid("message", expr);
      warnInvalidInside(Keywords.PRINTTYPE.name, expr);
      return false;
    }
    if (!validTypeTransformationExpression(getCallArgument(expr, 1))) {
      warnInvalidInside(Keywords.PRINTTYPE.name, expr);
      return false;
    }
    return true;
  }

  private boolean validPropTypeExpression(Node expr) {
    // The expression must have three children. The propType keyword, a
    // a string and a type transformation expression
    if (!checkParameterCount(expr, Keywords.PROPTYPE)) {
      return false;
    }
    if (!getCallArgument(expr, 0).isString()) {
      warnInvalid("property name", expr);
      warnInvalidInside(Keywords.PROPTYPE.name, expr);
      return false;
    }
    if (!validTypeTransformationExpression(getCallArgument(expr, 1))) {
      warnInvalidInside(Keywords.PROPTYPE.name, expr);
      return false;
    }
    return true;
  }

  /**
   * An operation expression is a cond or a mapunion
   */
  private boolean validOperationExpression(Node expr) {
    String name = getCallName(expr);
    Keywords keyword = nameToKeyword(name);
    switch (keyword) {
      case COND:
        return validConditionalExpression(expr);
      case MAPUNION:
        return validMapunionExpression(expr);
      case MAPRECORD:
        return validMaprecordExpression(expr);
      case TYPEOFVAR:
        return validTypeOfVarExpression(expr);
      case INSTANCEOF:
        return validInstanceOfExpression(expr);
      case PRINTTYPE:
        return validPrintTypeExpression(expr);
      case PROPTYPE:
        return validPropTypeExpression(expr);
      default:
        throw new IllegalStateException("Invalid type transformation operation");
    }
  }

  /**
   * Checks the structure of the AST of a type transformation expression
   * in @template T := TTLExp =:
   */
  private boolean validTypeTransformationExpression(Node expr) {
    if (!isValidExpression(expr)) {
      warnInvalidExpression("type transformation", expr);
      return false;
    }
    if (isTypeVar(expr) || isTypeName(expr)) {
      return true;
    }
    // Check for valid keyword
    String name = getCallName(expr);
    if (!isValidKeyword(name)) {
      warnInvalidExpression("type transformation", expr);
      return false;
    }
    Keywords keyword = nameToKeyword(name);
    // Check the rest of the expression depending on the kind
    switch (keyword.kind) {
      case TYPE_CONSTRUCTOR:
        return validTypeExpression(expr);
      case OPERATION:
        return validOperationExpression(expr);
      default:
        throw new IllegalStateException("Invalid type transformation expression");
    }
  }
}