refactor(@schematics/angular): organize use-application-builder migration

Reorganizes the `use-application-builder` migration by extracting the stylesheet-related logic into a separate, more focused file.

The key changes include:
- Moving stylesheet-related functions (`hasLessStylesheets`, `hasPostcssConfiguration`, `updateStyleImports`, and their helpers) from `migration.ts` into a new `stylesheet-updates.ts` file.
- Updating the main `migration.ts` file to import these functions from the new module.

Author: clydin

packages/schematics/angular/migrations/use-application-builder/migration.ts

@@ -7,15 +7,14 @@
  */
 
 import {
-  DirEntry,
   Rule,
   SchematicContext,
   SchematicsException,
   Tree,
   chain,
   externalSchematic,
 } from '@angular-devkit/schematics';
-import { basename, dirname, extname, join } from 'node:path/posix';
+import { dirname, join } from 'node:path/posix';
 import { removePackageJsonDependency } from '../../utility/dependencies';
 import {
   DependencyType,
@@ -27,13 +26,16 @@ import { JSONFile } from '../../utility/json-file';
 import { latestVersions } from '../../utility/latest-versions';
 import {
   TargetDefinition,
-  WorkspaceDefinition,
   allTargetOptions,
   allWorkspaceTargets,
   updateWorkspace,
 } from '../../utility/workspace';
 import { Builders, ProjectType } from '../../utility/workspace-models';
-import { findImports } from './css-import-lexer';
+import {
+  hasLessStylesheets,
+  hasPostcssConfiguration,
+  updateStyleImports,
+} from './stylesheet-updates';
 
 function* updateBuildTarget(
   projectName: string,
@@ -334,168 +336,6 @@ function updateProjects(tree: Tree, context: SchematicContext) {
   });
 }
 
-/**
- * Searches the schematic tree for files that have a `.less` extension.
- *
- * @param tree A Schematics tree instance to search
- * @returns true if Less stylesheet files are found; otherwise, false
- */
-function hasLessStylesheets(tree: Tree) {
-  const directories = [tree.getDir('/')];
-
-  let current;
-  while ((current = directories.pop())) {
-    for (const path of current.subfiles) {
-      if (path.endsWith('.less')) {
-        return true;
-      }
-    }
-
-    for (const path of current.subdirs) {
-      if (path === 'node_modules' || path.startsWith('.')) {
-        continue;
-      }
-      directories.push(current.dir(path));
-    }
-  }
-}
-
-/**
- * Searches for a Postcss configuration file within the workspace root
- * or any of the project roots.
- *
- * @param tree A Schematics tree instance to search
- * @param workspace A Workspace to check for projects
- * @returns true, if a Postcss configuration file is found; otherwise, false
- */
-function hasPostcssConfiguration(tree: Tree, workspace: WorkspaceDefinition) {
-  // Add workspace root
-  const searchDirectories = [''];
-
-  // Add each project root
-  for (const { root } of workspace.projects.values()) {
-    if (root) {
-      searchDirectories.push(root);
-    }
-  }
-
-  return searchDirectories.some(
-    (dir) =>
-      tree.exists(join(dir, 'postcss.config.json')) || tree.exists(join(dir, '.postcssrc.json')),
-  );
-}
-
-function* visit(
-  directory: DirEntry,
-): IterableIterator<[fileName: string, contents: string, sass: boolean]> {
-  for (const path of directory.subfiles) {
-    const sass = path.endsWith('.scss');
-    if (path.endsWith('.css') || sass) {
-      const entry = directory.file(path);
-      if (entry) {
-        const content = entry.content;
-
-        yield [entry.path, content.toString(), sass];
-      }
-    }
-  }
-
-  for (const path of directory.subdirs) {
-    if (path === 'node_modules' || path.startsWith('.')) {
-      continue;
-    }
-
-    yield* visit(directory.dir(path));
-  }
-}
-
-// Based on https://github.com/sass/dart-sass/blob/44d6bb6ac72fe6b93f5bfec371a1fffb18e6b76d/lib/src/importer/utils.dart
-function* potentialSassImports(
-  specifier: string,
-  base: string,
-  fromImport: boolean,
-): Iterable<string> {
-  const directory = join(base, dirname(specifier));
-  const extension = extname(specifier);
-  const hasStyleExtension = extension === '.scss' || extension === '.sass' || extension === '.css';
-  // Remove the style extension if present to allow adding the `.import` suffix
-  const filename = basename(specifier, hasStyleExtension ? extension : undefined);
-
-  if (hasStyleExtension) {
-    if (fromImport) {
-      yield join(directory, filename + '.import' + extension);
-      yield join(directory, '_' + filename + '.import' + extension);
-    }
-    yield join(directory, filename + extension);
-    yield join(directory, '_' + filename + extension);
-  } else {
-    if (fromImport) {
-      yield join(directory, filename + '.import.scss');
-      yield join(directory, filename + '.import.sass');
-      yield join(directory, filename + '.import.css');
-      yield join(directory, '_' + filename + '.import.scss');
-      yield join(directory, '_' + filename + '.import.sass');
-      yield join(directory, '_' + filename + '.import.css');
-    }
-    yield join(directory, filename + '.scss');
-    yield join(directory, filename + '.sass');
-    yield join(directory, filename + '.css');
-    yield join(directory, '_' + filename + '.scss');
-    yield join(directory, '_' + filename + '.sass');
-    yield join(directory, '_' + filename + '.css');
-  }
-}
-
-function updateStyleImports(tree: Tree, projectSourceRoot: string, buildTarget: TargetDefinition) {
-  const external = new Set<string>();
-  let needWorkspaceIncludePath = false;
-  for (const file of visit(tree.getDir(projectSourceRoot))) {
-    const [path, content, sass] = file;
-    const relativeBase = dirname(path);
-
-    let updater;
-    for (const { start, specifier, fromUse } of findImports(content, sass)) {
-      if (specifier[0] === '~') {
-        updater ??= tree.beginUpdate(path);
-        // start position includes the opening quote
-        updater.remove(start + 1, 1);
-      } else if (specifier[0] === '^') {
-        updater ??= tree.beginUpdate(path);
-        // start position includes the opening quote
-        updater.remove(start + 1, 1);
-        // Add to externalDependencies
-        external.add(specifier.slice(1));
-      } else if (
-        sass &&
-        [...potentialSassImports(specifier, relativeBase, !fromUse)].every(
-          (v) => !tree.exists(v),
-        ) &&
-        [...potentialSassImports(specifier, '/', !fromUse)].some((v) => tree.exists(v))
-      ) {
-        needWorkspaceIncludePath = true;
-      }
-    }
-    if (updater) {
-      tree.commitUpdate(updater);
-    }
-  }
-
-  if (needWorkspaceIncludePath) {
-    buildTarget.options ??= {};
-    buildTarget.options['stylePreprocessorOptions'] ??= {};
-    ((buildTarget.options['stylePreprocessorOptions'] as { includePaths?: string[] })[
-      'includePaths'
-    ] ??= []).push('.');
-  }
-
-  if (external.size > 0) {
-    buildTarget.options ??= {};
-    ((buildTarget.options['externalDependencies'] as string[] | undefined) ??= []).push(
-      ...external,
-    );
-  }
-}
-
 function deleteFile(path: string): Rule {
   return (tree) => {
     tree.delete(path);