Regression: unable to resolve schematics via package name

[Vortex375]

🐞 Bug report

Command (mark with an x)

• [ x ] generate
• [ x ] add
• [ x ] update

Is this a regression?

Yes, it used to work in Angular <= 8.x

Description

I have a library "@mycompany/mylib" and a separate package containing its schematics called "@mycompany/mylib-schematics".

I used to have this entry in the library's package.json file:

"schematics": "@mycompany/mylib-schematics/collection.json"

And this worked fine.

When executing, for example ng generate @mycompany/mylib:foo it would correctly resolve the collection.json file residing in "node_modules/@mycompany/mylib-schematics" and execute the schematic.

With Angular 9 this does not work anymore. I can no longer specify a package name in the "schematics" property of the package.json file. The path specified there is always resolved relative to the package.json location. I can make it work again if I change it to this:

"schematics": "../mylib-schematics/collection.json"

The problem is within packages/angular_devkit/schematics/tools/node-module-engine-host.ts:

  protected _resolveCollectionPath(name: string): string {
    let collectionPath: string | undefined = undefined;
    if (name.startsWith('.') || name.startsWith('/')) {
      name = resolve(name);
    }

    if (extname(name)) {
      // When having an extension let's just resolve the provided path.
      collectionPath = require.resolve(name, { paths: this.paths });
    } else {
      const packageJsonPath = require.resolve(join(name, 'package.json'), { paths: this.paths });
      const { schematics } = require(packageJsonPath);

      if (!schematics || typeof schematics !== 'string') {
        throw new NodePackageDoesNotSupportSchematics(name);
      }

// !!!
// the below line is wrong: it should only try to resolve it that way if the path starts with '.' or '/'
// (i.e. when dealing with a relative or absolute path)
// otherwise it should use require.resolve() like above
// !!!
      collectionPath = resolve(dirname(packageJsonPath), schematics);
    }

🔬 Minimal Reproduction

As described above, create a library and add a "collections" property to its package.json that points to another node_module, then try to "ng generate".

package.json of "@mycompany/mylib":

"schematics": "@mycompany/mylib-schematics/collection.json"

ng generate @mycompany/mylib:foo:

An unhandled exception occurred: Collection "@mycompany/mylib" cannot be resolved.

🔥 Exception or Error

[error] Error: Collection "@mycompany/mylib" cannot be resolved.
    at NodeModulesEngineHost._resolveCollectionPath (test-project/node_modules/@angular-devkit/schematics/tools/node-module-engine-host.js:55:15)
    at NodeModulesEngineHost.createCollectionDescription (test-project/node_modules/@angular-devkit/schematics/tools/file-system-engine-host-base.js:109:27)
    at SchematicEngine._createCollectionDescription (test-project/node_modules/@angular-devkit/schematics/src/engine/engine.js:147:40)
    at SchematicEngine.createCollection (test-project/node_modules/@angular-devkit/schematics/src/engine/engine.js:140:43)
    at GenerateCommand.getCollection (test-project/node_modules/@angular/cli/models/schematic-command.js:127:35)
    at GenerateCommand.initialize (test-project/node_modules/@angular/cli/models/schematic-command.js:43:37)
    at async GenerateCommand.initialize (test-project/node_modules/@angular/cli/commands/generate-impl.js:12:9)
    at async GenerateCommand.validateAndRun (test-project/node_modules/@angular/cli/models/command.js:124:9)
    at async Object.runCommand (test-project/node_modules/@angular/cli/models/command-runner.js:201:24)
    at async default_1 (test-project/node_modules/@angular/cli/lib/cli/index.js:62:31)

🌍 Your Environment

Angular CLI: 9.0.2
Node: 12.14.1
OS: darwin x64

Angular: 9.0.1
... animations, common, compiler, compiler-cli, core, forms
... language-service, localize, platform-browser
... platform-browser-dynamic, router
Ivy Workspace: Yes

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.900.2
@angular-devkit/build-angular      0.900.2
@angular-devkit/build-optimizer    0.900.2
@angular-devkit/build-webpack      0.900.2
@angular-devkit/core               9.0.2
@angular-devkit/schematics         9.0.2
@angular/cdk                       9.0.0
@angular/cli                       9.0.2
@angular/material                  9.0.0
@angular/material-moment-adapter   9.0.0
@ngtools/webpack                   9.0.2
@schematics/angular                9.0.2
@schematics/update                 0.900.2
rxjs                               6.5.3
typescript                         3.7.5
webpack                            4.41.2

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