Workspace dependency used only through a package.json imports alias is reported as unused #2952

What happened?

When a package imports a workspace package only through a package.json imports (#...) alias, the import resolves correctly and the imported export is treated as used, but the workspace package itself is reported as an unused dependency.

Possible cause

In try_package_imports_fallback in v3.30.0, external targets become NpmPackage, while internal targets become InternalPackageModule using the importing manifest's name. This appears to lose the target workspace package identity needed to credit the dependency.

Additional context

We import every workspace package through an imports alias ("#acme/log/*": "@acme/lib-log/*") so that application code does not depend on package names. In our monorepo this reports 99 workspace dependencies as unused. The workaround is to list each package in ignoreDependencies, which only accepts exact names.

We are also requesting glob support in ignoreDependencies in #2953 to reduce the maintenance cost of this workaround. That is a separate configuration enhancement; this issue asks for the used workspace dependency to be recognized without an ignore.

Related: #56 (support for package.json imports aliases; resolution itself works in this reproduction).

Reproduction

Create the following files in a new directory:

package.json
  { "name": "root", "private": true }

pnpm-workspace.yaml
  packages: ["packages/*"]

packages/lib/package.json
  { "name": "@repro/lib", "type": "module", "exports": { "./*": "./src/*.ts" } }

packages/lib/src/hello.ts
  export const hello = () => "hello";

packages/app/package.json
  {
    "name": "@repro/app",
    "type": "module",
    "private": true,
    "imports": { "#lib/*": "@repro/lib/*" },
    "dependencies": { "@repro/lib": "workspace:*" },
    "exports": { ".": "./src/index.ts" }
  }

packages/app/src/index.ts
  import { hello } from "#lib/hello";
  console.log(hello());

Run from the root directory:

$ pnpm install
$ fallow dead-code
● Unused dependencies (1)
  @repro/lib (packages/app/package.json)

Expected behavior

@repro/lib is credited as used by @repro/app, the same as when an imports alias points to an external npm package. hello is already treated as used, so only the dependency credit is missing.

Fallow version

3.30.0

Operating system

Linux

Configuration

None (default config).