Function parseForLoopParameters

packages/compiler/src/render3/r3_control_flow.ts:354–490

Parses the parameters of a `for` loop block.

(
  block: html.Block,
  errors: ParseError[],
  bindingParser: BindingParser,
)

/** Parses the parameters of a `for` loop block. */
function parseForLoopParameters(
  block: html.Block,
  errors: ParseError[],
  bindingParser: BindingParser,
) {
  if (block.parameters.length === 0) {
    errors.push(new ParseError(block.startSourceSpan, '@for loop does not have an expression'));
    return null;
  }

  const [expressionParam, ...secondaryParams] = block.parameters;
  const match = stripOptionalParentheses(expressionParam, errors)?.match(
    FOR_LOOP_EXPRESSION_PATTERN,
  );

  if (!match || match[2].trim().length === 0) {
    errors.push(
      new ParseError(
        expressionParam.sourceSpan,
        'Cannot parse expression. @for loop expression must match the pattern "<identifier> of <expression>"',
      ),
    );
    return null;
  }

  const [, itemName, rawExpression] = match;
  if (ALLOWED_FOR_LOOP_LET_VARIABLES.has(itemName)) {
    errors.push(
      new ParseError(
        expressionParam.sourceSpan,
        `@for loop item name cannot be one of ${Array.from(ALLOWED_FOR_LOOP_LET_VARIABLES).join(
          ', ',
        )}.`,
      ),
    );
  }

  // `expressionParam.expression` contains the variable declaration and the expression of the
  // for...of statement, i.e. 'user of users' The variable of a ForOfStatement is _only_ the "const
  // user" part and does not include "of x".
  const variableName = expressionParam.expression.split(' ')[0];
  const variableSpan = new ParseSourceSpan(
    expressionParam.sourceSpan.start,
    expressionParam.sourceSpan.start.moveBy(variableName.length),
  );
  const result = {
    itemName: new t.Variable(itemName, '$implicit', variableSpan, variableSpan),
    trackBy: null as {expression: ASTWithSource; keywordSpan: ParseSourceSpan} | null,
    expression: parseBlockParameterToBinding(expressionParam, bindingParser, rawExpression),
    context: Array.from(ALLOWED_FOR_LOOP_LET_VARIABLES, (variableName) => {
      // Give ambiently-available context variables empty spans at the end of
      // the start of the `for` block, since they are not explicitly defined.
      const emptySpanAfterForBlockStart = new ParseSourceSpan(
        block.startSourceSpan.end,
        block.startSourceSpan.end,
      );
      return new t.Variable(
        variableName,