Function ɵɵprojection

packages/core/src/render3/instructions/projection.ts:149–205

(
  nodeIndex: number,
  selectorIndex: number = 0,
  attrs?: TAttributes | null,
  fallbackTemplateFn?: ComponentTemplate<unknown>,
  fallbackDecls?: number,
  fallbackVars?: number,
)

 * @codeGenApi
 */
export function ɵɵprojection(
  nodeIndex: number,
  selectorIndex: number = 0,
  attrs?: TAttributes | null,
  fallbackTemplateFn?: ComponentTemplate<unknown>,
  fallbackDecls?: number,
  fallbackVars?: number,
): void {
  const lView = getLView();
  const tView = getTView();
  const fallbackIndex = fallbackTemplateFn ? nodeIndex + 1 : null;

  // Fallback content needs to be declared no matter whether the slot is empty since different
  // instances of the component may or may not insert it. Also it needs to be declare *before*
  // the projection node in order to work correctly with hydration.
  if (fallbackIndex !== null) {
    declareNoDirectiveHostTemplate(
      lView,
      tView,
      fallbackIndex,
      fallbackTemplateFn!,
      fallbackDecls!,
      fallbackVars!,
      null,
      attrs,
    );
  }

  const tProjectionNode = getOrCreateTNode(
    tView,
    HEADER_OFFSET + nodeIndex,
    TNodeType.Projection,
    null,
    attrs || null,
  );

  // We can't use viewData[HOST_NODE] because projection nodes can be nested in embedded views.
  if (tProjectionNode.projection === null) {
    tProjectionNode.projection = selectorIndex;
  }

  // `<ng-content>` has no content. Even if there's fallback
  // content, the fallback is shown next to it.
  setCurrentTNodeAsNotParent();

  const hydrationInfo = lView[HYDRATION];
  const isNodeCreationMode = !hydrationInfo || isInSkipHydrationBlock();
  const componentHostNode = lView[DECLARATION_COMPONENT_VIEW][T_HOST] as TElementNode;
  const isEmpty = componentHostNode.projection![tProjectionNode.projection] === null;

  if (isEmpty && fallbackIndex !== null) {
    insertFallbackContent(lView, tView, fallbackIndex);
  } else if (isNodeCreationMode && !isDetachedByI18n(tProjectionNode)) {
    // re-distribution of projectable nodes is stored on a component's view level
    applyProjection(tView, lView, tProjectionNode);
  }
}