Function parseFunction

packages/babel-parser/src/parser/statement.ts:1443–1495

(
    this: Parser,
    node: Undone<T>,
    flags: ParseFunctionFlag = ParseFunctionFlag.Expression,
  )

  // ParseFunctionFlag.Declaration flag).

  parseFunction<T extends N.NormalFunction>(
    this: Parser,
    node: Undone<T>,
    flags: ParseFunctionFlag = ParseFunctionFlag.Expression,
  ): T {
    const hangingDeclaration = flags & ParseFunctionFlag.HangingDeclaration;
    const isDeclaration = !!(flags & ParseFunctionFlag.Declaration);
    const requireId = isDeclaration && !(flags & ParseFunctionFlag.NullableId);
    const isAsync = !!(flags & ParseFunctionFlag.Async);

    this.initFunction(node, isAsync);

    if (this.match(tt.star)) {
      if (hangingDeclaration) {
        this.raise(
          Errors.GeneratorInSingleStatementContext,
          this.state.startLoc,
        );
      }
      this.next(); // eat *
      node.generator = true;
    }

    if (isDeclaration) {
      node.id = this.parseFunctionId(requireId);
    }

    this.scope.enter(ScopeFlag.FUNCTION);
    this.prodParam.enter(functionFlags(isAsync, node.generator));

    if (!isDeclaration) {
      node.id = this.parseFunctionId();
    }

    this.parseFunctionParams(node, /* isConstructor */ false);

    this.parseFunctionBodyAndFinish(
      node,
      isDeclaration ? "FunctionDeclaration" : "FunctionExpression",
    );

    this.prodParam.exit();
    this.scope.exit();

    if (isDeclaration && !hangingDeclaration) {
      // We need to register this _after_ parsing the function body
      // because of TypeScript body-less function declarations,
      // which shouldn't be added to the scope.
      this.registerFunctionStatementId(node as T);
    }

    return node as T;
  }

  parseFunctionId(requireId?: boolean): N.Identifier | undefined | null {
    return requireId || tokenIsIdentifier(this.state.type)