Function parseLetParameter

packages/compiler/src/render3/r3_control_flow.ts:496–570

Parses the `let` parameter of a `for` loop block.

(
  sourceSpan: ParseSourceSpan,
  expression: string,
  span: ParseSourceSpan,
  loopItemName: string,
  context: t.Variable[],
  errors: ParseError[],
)

/** Parses the `let` parameter of a `for` loop block. */
function parseLetParameter(
  sourceSpan: ParseSourceSpan,
  expression: string,
  span: ParseSourceSpan,
  loopItemName: string,
  context: t.Variable[],
  errors: ParseError[],
): void {
  const parts = expression.split(',');
  let startSpan = span.start;
  for (const part of parts) {
    const expressionParts = part.split('=');
    const name = expressionParts.length === 2 ? expressionParts[0].trim() : '';
    const variableName = expressionParts.length === 2 ? expressionParts[1].trim() : '';

    if (name.length === 0 || variableName.length === 0) {
      errors.push(
        new ParseError(
          sourceSpan,
          `Invalid @for loop "let" parameter. Parameter should match the pattern "<name> = <variable name>"`,
        ),
      );
    } else if (!ALLOWED_FOR_LOOP_LET_VARIABLES.has(variableName)) {
      errors.push(
        new ParseError(
          sourceSpan,
          `Unknown "let" parameter variable "${variableName}". The allowed variables are: ${Array.from(
            ALLOWED_FOR_LOOP_LET_VARIABLES,
          ).join(', ')}`,
        ),
      );
    } else if (name === loopItemName) {
      errors.push(
        new ParseError(
          sourceSpan,
          `Invalid @for loop "let" parameter. Variable cannot be called "${loopItemName}"`,
        ),
      );
    } else if (context.some((v) => v.name === name)) {
      errors.push(
        new ParseError(sourceSpan, `Duplicate "let" parameter variable "${variableName}"`),
      );
    } else {
      const [, keyLeadingWhitespace, keyName] =
        expressionParts[0].match(CHARACTERS_IN_SURROUNDING_WHITESPACE_PATTERN) ?? [];
      const keySpan =
        keyLeadingWhitespace !== undefined && expressionParts.length === 2
          ? new ParseSourceSpan(
              /* strip leading spaces */
              startSpan.moveBy(keyLeadingWhitespace.length),
              /* advance to end of the variable name */
              startSpan.moveBy(keyLeadingWhitespace.length + keyName.length),
            )
          : span;

      let valueSpan: ParseSourceSpan | undefined = undefined;
      if (expressionParts.length === 2) {
        const [, valueLeadingWhitespace, implicit] =