sucrase/dist/transformers/TypeScriptTransformer.mjs

import {TokenType as tt} from "../parser/tokenizer/types";

import isIdentifier from "../util/isIdentifier";

import Transformer from "./Transformer";

export default class TypeScriptTransformer extends Transformer {
  constructor(
     rootTransformer,
     tokens,
     isImportsTransformEnabled,
  ) {
    super();this.rootTransformer = rootTransformer;this.tokens = tokens;this.isImportsTransformEnabled = isImportsTransformEnabled;;
  }

  process() {
    if (
      this.rootTransformer.processPossibleArrowParamEnd() ||
      this.rootTransformer.processPossibleAsyncArrowWithTypeParams() ||
      this.rootTransformer.processPossibleTypeRange()
    ) {
      return true;
    }
    if (
      this.tokens.matches1(tt._public) ||
      this.tokens.matches1(tt._protected) ||
      this.tokens.matches1(tt._private) ||
      this.tokens.matches1(tt._abstract) ||
      this.tokens.matches1(tt._readonly) ||
      this.tokens.matches1(tt._override) ||
      this.tokens.matches1(tt.nonNullAssertion)
    ) {
      this.tokens.removeInitialToken();
      return true;
    }
    if (this.tokens.matches1(tt._enum) || this.tokens.matches2(tt._const, tt._enum)) {
      this.processEnum();
      return true;
    }
    if (
      this.tokens.matches2(tt._export, tt._enum) ||
      this.tokens.matches3(tt._export, tt._const, tt._enum)
    ) {
      this.processEnum(true);
      return true;
    }
    return false;
  }

  processEnum(isExport = false) {
    // We might have "export const enum", so just remove all relevant tokens.
    this.tokens.removeInitialToken();
    while (this.tokens.matches1(tt._const) || this.tokens.matches1(tt._enum)) {
      this.tokens.removeToken();
    }
    const enumName = this.tokens.identifierName();
    this.tokens.removeToken();
    if (isExport && !this.isImportsTransformEnabled) {
      this.tokens.appendCode("export ");
    }
    this.tokens.appendCode(`var ${enumName}; (function (${enumName})`);
    this.tokens.copyExpectedToken(tt.braceL);
    this.processEnumBody(enumName);
    this.tokens.copyExpectedToken(tt.braceR);
    if (isExport && this.isImportsTransformEnabled) {
      this.tokens.appendCode(`)(${enumName} || (exports.${enumName} = ${enumName} = {}));`);
    } else {
      this.tokens.appendCode(`)(${enumName} || (${enumName} = {}));`);
    }
  }

  /**
   * Transform an enum into equivalent JS. This has complexity in a few places:
   * - TS allows string enums, numeric enums, and a mix of the two styles within an enum.
   * - Enum keys are allowed to be referenced in later enum values.
   * - Enum keys are allowed to be strings.
   * - When enum values are omitted, they should follow an auto-increment behavior.
   */
  processEnumBody(enumName) {
    // Code that can be used to reference the previous enum member, or null if this is the first
    // enum member.
    let previousValueCode = null;
    while (true) {
      if (this.tokens.matches1(tt.braceR)) {
        break;
      }
      const {nameStringCode, variableName} = this.extractEnumKeyInfo(this.tokens.currentToken());
      this.tokens.removeInitialToken();

      if (
        this.tokens.matches3(tt.eq, tt.string, tt.comma) ||
        this.tokens.matches3(tt.eq, tt.string, tt.braceR)
      ) {
        this.processStringLiteralEnumMember(enumName, nameStringCode, variableName);
      } else if (this.tokens.matches1(tt.eq)) {
        this.processExplicitValueEnumMember(enumName, nameStringCode, variableName);
      } else {
        this.processImplicitValueEnumMember(
          enumName,
          nameStringCode,
          variableName,
          previousValueCode,
        );
      }
      if (this.tokens.matches1(tt.comma)) {
        this.tokens.removeToken();
      }

      if (variableName != null) {
        previousValueCode = variableName;
      } else {
        previousValueCode = `${enumName}[${nameStringCode}]`;
      }
    }
  }

  /**
   * Detect name information about this enum key, which will be used to determine which code to emit
   * and whether we should declare a variable as part of this declaration.
   *
   * Some cases to keep in mind:
   * - Enum keys can be implicitly referenced later, e.g. `X = 1, Y = X`. In Sucrase, we implement
   *   this by declaring a variable `X` so that later expressions can use it.
   * - In addition to the usual identifier key syntax, enum keys are allowed to be string literals,
   *   e.g. `"hello world" = 3,`. Template literal syntax is NOT allowed.
   * - Even if the enum key is defined as a string literal, it may still be referenced by identifier
   *   later, e.g. `"X" = 1, Y = X`. That means that we need to detect whether or not a string
   *   literal is identifier-like and emit a variable if so, even if the declaration did not use an
   *   identifier.
   * - Reserved keywords like `break` are valid enum keys, but are not valid to be referenced later
   *   and would be a syntax error if we emitted a variable, so we need to skip the variable
   *   declaration in those cases.
   *
   * The variableName return value captures these nuances: if non-null, we can and must emit a
   * variable declaration, and if null, we can't and shouldn't.
   */
  extractEnumKeyInfo(nameToken) {
    if (nameToken.type === tt.name) {
      const name = this.tokens.identifierNameForToken(nameToken);
      return {
        nameStringCode: `"${name}"`,
        variableName: isIdentifier(name) ? name : null,
      };
    } else if (nameToken.type === tt.string) {
      const name = this.tokens.stringValueForToken(nameToken);
      return {
        nameStringCode: this.tokens.code.slice(nameToken.start, nameToken.end),
        variableName: isIdentifier(name) ? name : null,
      };
    } else {
      throw new Error("Expected name or string at beginning of enum element.");
    }
  }

  /**
   * Handle an enum member where the RHS is just a string literal (not omitted, not a number, and
   * not a complex expression). This is the typical form for TS string enums, and in this case, we
   * do *not* create a reverse mapping.
   *
   * This is called after deleting the key token, when the token processor is at the equals sign.
   *
   * Example 1:
   * someKey = "some value"
   * ->
   * const someKey = "some value"; MyEnum["someKey"] = someKey;
   *
   * Example 2:
   * "some key" = "some value"
   * ->
   * MyEnum["some key"] = "some value";
   */
  processStringLiteralEnumMember(
    enumName,
    nameStringCode,
    variableName,
  ) {
    if (variableName != null) {
      this.tokens.appendCode(`const ${variableName}`);
      // =
      this.tokens.copyToken();
      // value string
      this.tokens.copyToken();
      this.tokens.appendCode(`; ${enumName}[${nameStringCode}] = ${variableName};`);
    } else {
      this.tokens.appendCode(`${enumName}[${nameStringCode}]`);
      // =
      this.tokens.copyToken();
      // value string
      this.tokens.copyToken();
      this.tokens.appendCode(";");
    }
  }

  /**
   * Handle an enum member initialized with an expression on the right-hand side (other than a
   * string literal). In these cases, we should transform the expression and emit code that sets up
   * a reverse mapping.
   *
   * The TypeScript implementation of this operation distinguishes between expressions that can be
   * "constant folded" at compile time (i.e. consist of number literals and simple math operations
   * on those numbers) and ones that are dynamic. For constant expressions, it emits the resolved
   * numeric value, and auto-incrementing is only allowed in that case. Evaluating expressions at
   * compile time would add significant complexity to Sucrase, so Sucrase instead leaves the
   * expression as-is, and will later emit something like `MyEnum["previousKey"] + 1` to implement
   * auto-incrementing.
   *
   * This is called after deleting the key token, when the token processor is at the equals sign.
   *
   * Example 1:
   * someKey = 1 + 1
   * ->
   * const someKey = 1 + 1; MyEnum[MyEnum["someKey"] = someKey] = "someKey";
   *
   * Example 2:
   * "some key" = 1 + 1
   * ->
   * MyEnum[MyEnum["some key"] = 1 + 1] = "some key";
   */
  processExplicitValueEnumMember(
    enumName,
    nameStringCode,
    variableName,
  ) {
    const rhsEndIndex = this.tokens.currentToken().rhsEndIndex;
    if (rhsEndIndex == null) {
      throw new Error("Expected rhsEndIndex on enum assign.");
    }

    if (variableName != null) {
      this.tokens.appendCode(`const ${variableName}`);
      this.tokens.copyToken();
      while (this.tokens.currentIndex() < rhsEndIndex) {
        this.rootTransformer.processToken();
      }
      this.tokens.appendCode(
        `; ${enumName}[${enumName}[${nameStringCode}] = ${variableName}] = ${nameStringCode};`,
      );
    } else {
      this.tokens.appendCode(`${enumName}[${enumName}[${nameStringCode}]`);
      this.tokens.copyToken();
      while (this.tokens.currentIndex() < rhsEndIndex) {
        this.rootTransformer.processToken();
      }
      this.tokens.appendCode(`] = ${nameStringCode};`);
    }
  }

  /**
   * Handle an enum member with no right-hand side expression. In this case, the value is the
   * previous value plus 1, or 0 if there was no previous value. We should also always emit a
   * reverse mapping.
   *
   * Example 1:
   * someKey2
   * ->
   * const someKey2 = someKey1 + 1; MyEnum[MyEnum["someKey2"] = someKey2] = "someKey2";
   *
   * Example 2:
   * "some key 2"
   * ->
   * MyEnum[MyEnum["some key 2"] = someKey1 + 1] = "some key 2";
   */
  processImplicitValueEnumMember(
    enumName,
    nameStringCode,
    variableName,
    previousValueCode,
  ) {
    let valueCode = previousValueCode != null ? `${previousValueCode} + 1` : "0";
    if (variableName != null) {
      this.tokens.appendCode(`const ${variableName} = ${valueCode}; `);
      valueCode = variableName;
    }
    this.tokens.appendCode(
      `${enumName}[${enumName}[${nameStringCode}] = ${valueCode}] = ${nameStringCode};`,
    );
  }
}