Apply Prettier Schematic

apply-prettier.ts

import { Rule, Tree } from '@angular-devkit/schematics';
import * as prettier from 'prettier';
import { Observable } from 'rxjs';

export default function(): Rule {
  return (tree: Tree) =>
    new Observable<Tree>(o => {
      prettier.resolveConfig(process.cwd()).then(prettierConfig => {
        if (!prettierConfig) {
          o.error(new Error('Could not resolve prettier configuration'));
          return;
        }

        tree.visit(path => {
          if (path.endsWith('.tsx') || path.endsWith('.ts') || path.endsWith('.jsx') || path.endsWith('.js')) {
            const content = tree.read(path);
            if (content) {
              const formatted = prettier.format(content.toString(), prettierConfig);
              tree.overwrite(path, formatted);
            }
          }

          return false;
        });
        o.next(tree);
        o.complete();
      });
    });
}

collection.json

{
  "$schema": "../node_modules/@angular-devkit/schematics/collection-schema.json",
  "schematics": {
    "apply-prettier": {
      "factory": "./apply-prettier/index",
      "description": "Applies prettier to a tree of files",
      "private": true
    }
  }
}

usage.ts

// Simple Usage Example

import { strings } from '@angular-devkit/core';
import {
  apply,
  chain,
  filter,
  mergeWith,
  noop,
  Rule,
  schematic,
  SchematicContext,
  template,
  Tree,
  url
} from '@angular-devkit/schematics';
import { Schema as Options } from './schema';

export default function(options: Options): Rule {
  return chain([
    (_tree: Tree, _context: SchematicContext) => {
      const templateSource = apply(url('./files'), [
        template({
          ...strings,
          ...options
        }),
        schematic('apply-prettier', {}) // <- ❤️
      ]);

      return mergeWith(templateSource);
    }
  ]);
}

@keawade nice! thanks for you amendment :)