Function createForLoop

packages/compiler/src/render3/r3_control_flow.ts:153–223

(
  ast: html.Block,
  connectedBlocks: html.Block[],
  visitor: html.Visitor,
  bindingParser: BindingParser,
)

/** Creates a `for` loop block from an HTML AST node. */
export function createForLoop(
  ast: html.Block,
  connectedBlocks: html.Block[],
  visitor: html.Visitor,
  bindingParser: BindingParser,
): {node: t.ForLoopBlock | null; errors: ParseError[]} {
  const errors: ParseError[] = [];
  const params = parseForLoopParameters(ast, errors, bindingParser);
  let node: t.ForLoopBlock | null = null;
  let empty: t.ForLoopBlockEmpty | null = null;

  for (const block of connectedBlocks) {
    if (block.name === 'empty') {
      if (empty !== null) {
        errors.push(new ParseError(block.sourceSpan, '@for loop can only have one @empty block'));
      } else if (block.parameters.length > 0) {
        errors.push(new ParseError(block.sourceSpan, '@empty block cannot have parameters'));
      } else {
        empty = new t.ForLoopBlockEmpty(
          html.visitAll(visitor, block.children, block.children),
          block.sourceSpan,
          block.startSourceSpan,
          block.endSourceSpan,
          block.nameSpan,
          block.i18n,
        );
      }
    } else {
      errors.push(new ParseError(block.sourceSpan, `Unrecognized @for loop block "${block.name}"`));
    }
  }

  if (params !== null) {
    // The `for` block has a main span that includes the `empty` branch. For only the span of the
    // main `for` body, use `mainSourceSpan`.
    const endSpan = empty?.endSourceSpan ?? ast.endSourceSpan;
    const sourceSpan = new ParseSourceSpan(
      ast.sourceSpan.start,
      endSpan?.end ?? ast.sourceSpan.end,
    );
    let trackExpression: ASTWithSource | null;
    let trackKeywordSpan: ParseSourceSpan | null;

    if (params.trackBy === null) {
      trackExpression = trackKeywordSpan = null;
      errors.push(new ParseError(ast.startSourceSpan, '@for loop must have a "track" expression'));
    } else {
      trackExpression = params.trackBy.expression;
      trackKeywordSpan = params.trackBy.keywordSpan;
      validateTrackByExpression(params.trackBy.expression, params.trackBy.keywordSpan, errors);
    }

    node = new t.ForLoopBlock(
      params.itemName,
      params.expression,
      trackExpression,
      trackKeywordSpan,
      params.context,