Function ingestForBlock

packages/compiler/src/template/pipeline/src/ingest.ts:906–1007

* Ingest an `@for` block into the given `ViewCompilation`.

(unit: ViewCompilationUnit, forBlock: t.ForLoopBlock)

 * Ingest an `@for` block into the given `ViewCompilation`.
 */
function ingestForBlock(unit: ViewCompilationUnit, forBlock: t.ForLoopBlock): void {
  const repeaterView = unit.job.allocateView(unit.xref);

  // We copy TemplateDefinitionBuilder's scheme of creating names for `$count` and `$index`
  // that are suffixed with special information, to disambiguate which level of nested loop
  // the below aliases refer to.
  // TODO: We should refactor Template Pipeline's variable phases to gracefully handle
  // shadowing, and arbitrarily many levels of variables depending on each other.
  const indexName = `ɵ$index_${repeaterView.xref}`;
  const countName = `ɵ$count_${repeaterView.xref}`;
  const indexVarNames = new Set<string>();

  // Set all the context variables and aliases available in the repeater.
  repeaterView.contextVariables.set(forBlock.item.name, forBlock.item.value);

  for (const variable of forBlock.contextVariables) {
    if (variable.value === '$index') {
      indexVarNames.add(variable.name);
    }
    if (variable.name === '$index') {
      repeaterView.contextVariables.set('$index', variable.value).set(indexName, variable.value);
    } else if (variable.name === '$count') {
      repeaterView.contextVariables.set('$count', variable.value).set(countName, variable.value);
    } else {
      repeaterView.aliases.add({
        kind: ir.SemanticVariableKind.Alias,
        name: null,
        identifier: variable.name,
        expression: getComputedForLoopVariableExpression(variable, indexName, countName),
      });
    }
  }

  let track: o.Expression;

  if (forBlock.trackBy === null) {
    // `@for` without a `track` is invalid and it produces a parser error.
    // Put a placeholder here so we don't need to account for it throughout the pipeline.
    track = o.variable('$index');
  } else {
    track = convertAst(
      forBlock.trackBy,
      unit.job,
      convertSourceSpan(forBlock.trackBy.span, forBlock.sourceSpan),
    );
  }

  ingestNodes(repeaterView, forBlock.children);

  let emptyView: ViewCompilationUnit | null = null;
  let emptyTagName: string | null = null;
  if (forBlock.empty !== null) {
    emptyView = unit.job.allocateView(unit.xref);
    ingestNodes(emptyView, forBlock.empty.children);
    emptyTagName = ingestControlFlowInsertionPoint(unit, emptyView.xref, forBlock.empty);
  }

  const varNames: ir.RepeaterVarNames = {