feat(use): add --from-npm CLI flag

README.md

@@ -211,11 +211,13 @@ calling their respective binaries outside of projects defining the
 Download the selected package managers and store them inside a tarball
 suitable for use with `corepack install -g`.
 
-### `corepack use <name[@<version>]>`
+### `corepack use <name[@<version>]> [--from-npm]`
 
 When run, this command will retrieve the latest release matching the provided
 descriptor, assign it to the project's package.json file, and automatically
 perform an install.
+When passing the `--from-npm` flag, Corepack will use the latest version of the
+package with the corresponding name from the npm registry.
 
 ### `corepack up`
 

sources/commands/Base.ts

@@ -39,14 +39,21 @@ export abstract class BaseCommand extends Command<Context> {
     const {data, indent} = nodeUtils.readPackageJson(content);
 
     const previousPackageManager = data.packageManager ?? `unknown`;
-    data.packageManager = `${info.locator.name}@${info.locator.reference}+${info.hash}`;
+    data.packageManager = `${info.locator.name}@${info.locator.reference}${URL.canParse(info.locator.reference) ? `#` : `+`}${info.hash}`;
 
     const newContent = nodeUtils.normalizeLineEndings(content, `${JSON.stringify(data, null, indent)}\n`);
     await fs.promises.writeFile(lookup.target, newContent, `utf8`);
 
-    const command = this.context.engine.getPackageManagerSpecFor(info.locator).commands?.use ?? null;
-    if (command === null)
+    let command: Array<string>;
+    try {
+      const _command = this.context.engine.getPackageManagerSpecFor(info.locator).commands?.use;
+      if (_command == null)
+        return 0;
+
+      command = _command;
+    } catch {
       return 0;
+    }
 
     // Adding it into the environment avoids breaking package managers that
     // don't expect those options.

sources/commands/Use.ts

@@ -1,12 +1,20 @@
 import {Command, Option, UsageError} from 'clipanion';
 
+
+import {fetchLatestStableVersion}    from '../corepackUtils';
+
 import {BaseCommand}                 from './Base';
 
+
 export class UseCommand extends BaseCommand {
   static paths = [
     [`use`],
   ];
 
+  fromNpm = Option.Boolean(`--from-npm`, false, {
+    description: `If true, the package manager will be installed from the npm registry`,
+  });
+
   static usage = Command.Usage({
     description: `Define the package manager to use for the current project`,
     details: `
@@ -17,23 +25,51 @@ export class UseCommand extends BaseCommand {
     examples: [[
       `Configure the project to use the latest Yarn release`,
       `corepack use yarn`,
+    ], [
+      `Configure the project to use the latest Yarn release available from the "yarn" package on the npm registry`,
+      `corepack use yarn --from-npm`,
     ]],
   });
 
   pattern = Option.String();
 
   async execute() {
-    const [descriptor] = await this.resolvePatternsToDescriptors({
-      patterns: [this.pattern],
-    });
+    let packageManagerInfo: Parameters<typeof this.setLocalPackageManager>[0];
+    if (this.fromNpm) {
+      const registry = {
+        type: `npm` as const,
+        package: this.pattern,
+      };
+      const versionWithHash = await fetchLatestStableVersion(registry);
+      const [version, hash] = versionWithHash.split(`+`);
+      const location = `https://registry.npmjs.com/${this.pattern}/-/${this.pattern}-${version}.tgz`;
+      packageManagerInfo = {
+        locator: {
+          name: this.pattern,
+          reference: location,
+        },
+        spec: {
+          bin: {},
+          registry,
+          url: location,
+        },
+        hash,
+        location,
+        bin: undefined,
+      };
+    } else {
+      const [descriptor] = await this.resolvePatternsToDescriptors({
+        patterns: [this.pattern],
+      });
 
-    const resolved = await this.context.engine.resolveDescriptor(descriptor, {allowTags: true, useCache: false});
-    if (resolved === null)
-      throw new UsageError(`Failed to successfully resolve '${descriptor.range}' to a valid ${descriptor.name} release`);
+      const resolved = await this.context.engine.resolveDescriptor(descriptor, {allowTags: true, useCache: false});
+      if (resolved === null)
+        throw new UsageError(`Failed to successfully resolve '${descriptor.range}' to a valid ${descriptor.name} release`);
 
-    this.context.stdout.write(`Installing ${resolved.name}@${resolved.reference} in the project...\n`);
+      this.context.stdout.write(`Installing ${resolved.name}@${resolved.reference} in the project...\n`);
 
-    const packageManagerInfo = await this.context.engine.ensurePackageManager(resolved);
+      packageManagerInfo = await this.context.engine.ensurePackageManager(resolved);
+    }
     await this.setLocalPackageManager(packageManagerInfo);
   }
 }

sources/specUtils.ts

@@ -20,7 +20,7 @@ export function parseSpec(raw: unknown, source: string, {enforceExactVersion = t
 
     const name = atIndex === -1 ? raw : raw.slice(0, -1);
     if (!isSupportedPackageManager(name))
-      throw new UsageError(`Unsupported package manager specification (${name})`);
+      throw new UsageError(`Unsupported package manager specification (${name}). Consider using the \`--from-npm\` flag if you meant to use the npm package \`${name}\` as your package manager`);
 
     return {
       name, range: `*`,
@@ -33,7 +33,7 @@ export function parseSpec(raw: unknown, source: string, {enforceExactVersion = t
   const isURL = URL.canParse(range);
   if (!isURL) {
     if (enforceExactVersion && !semver.valid(range))
-      throw new UsageError(`Invalid package manager specification in ${source} (${raw}); expected a semver version${enforceExactVersion ? `` : `, range, or tag`}`);
+      throw new UsageError(`Invalid package manager specification in ${source} (${raw}); expected a semver version`);
 
     if (!isSupportedPackageManager(name)) {
       throw new UsageError(`Unsupported package manager specification (${raw})`);

tests/Use.test.ts

@@ -64,4 +64,23 @@ describe(`UseCommand`, () => {
       });
     });
   });
+
+  it(`should accept --from-npm CLI flag`, async () => {
+    await xfs.mktempPromise(async cwd => {
+      await expect(runCli(cwd, [`use`, `test`])).resolves.toMatchObject({
+        exitCode: 1,
+        stdout: /Invalid package manager specification in CLI arguments. Consider adding the `--from-npm` flag if you meant to use the npm package `test` as your package manager/,
+        stderr: ``,
+      });
+
+      await expect(runCli(cwd, [`use`, `test`, `--from-npm`])).resolves.toMatchObject({
+        exitCode: 0,
+        stderr: ``,
+      });
+
+      await expect(xfs.readJsonPromise(ppath.join(cwd, `package.json`))).resolves.toMatchObject({
+        packageManager: `test@https://registry.npmjs.com/test/-/test-3.3.0.tgz#sha1.a2b56c6aa386c5732065793e8d9d92074a9cdd41`,
+      });
+    });
+  });
 });