Function mergeWithExistingDefinition

packages/core/src/render3/hmr.ts:125–155

* Merges two component definitions while preseving the original one in place. * @param currentDef Definition that should receive the new metadata. * @param newDef Source of the new metadata.

(
  currentDef: ComponentDef<unknown>,
  newDef: ComponentDef<unknown>,
)

 * @param newDef Source of the new metadata.
 */
function mergeWithExistingDefinition(
  currentDef: ComponentDef<unknown>,
  newDef: ComponentDef<unknown>,
) {
  // Clone the current definition since we reference its original data further
  // down in the replacement process (e.g. when destroying the renderer).
  const clone = {...currentDef};

  // Assign the new metadata in place while preserving the object literal. It's important to
  // Keep the object in place, because there can be references to it, for example in the
  // `directiveDefs` of another definition.
  const replacement = Object.assign(currentDef, newDef, {
    // We need to keep the existing directive and pipe defs, because they can get patched on
    // by a call to `setComponentScope` from a module file. That call won't make it into the
    // HMR replacement function, because it lives in an entirely different file.
    directiveDefs: clone.directiveDefs,
    pipeDefs: clone.pipeDefs,

    // Preserve the old `setInput` function, because it has some state.
    // This is fine, because the component instance is preserved as well.
    setInput: clone.setInput,

    // Externally this is redundant since we redeclare the definition using the original type.
    // Internally we may receive a definition with an alternate, but identical, type so we have
    // to ensure that the original one is preserved.
    type: clone.type,
  });

  ngDevMode && assertEqual(replacement, currentDef, 'Expected definition to be merged in place');
  return {newDef: replacement, oldDef: clone};
}

/**
 * Finds all LViews matching a specific component definition and recreates them.