feat: add --skip-install to use and up

README.md

@@ -277,6 +277,9 @@ 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.
 
+Pass `--skip-install` to update `package.json` without installing the project's
+dependencies. The selected package manager is still downloaded and verified.
+
 ### `corepack up`
 
 Retrieve the latest available version for the current major release line of
@@ -289,6 +292,9 @@ range specified in `devEngines.packageManager.version`, or fallback to the
 same major line. Should you need to upgrade to a new major, use an explicit
 `corepack use {name}@latest` call (or simply `corepack use {name}`).
 
+Pass `--skip-install` to update `package.json` without installing the project's
+dependencies. The selected package manager is still downloaded and verified.
+
 ## Environment Variables
 
 - `COREPACK_DEFAULT_TO_LATEST` can be set to `0` in order to instruct Corepack

sources/commands/Base.ts

@@ -35,11 +35,14 @@ export abstract class BaseCommand extends Command<Context> {
     return resolvedSpecs;
   }
 
-  async setAndInstallLocalPackageManager(info: PreparedPackageManagerInfo) {
+  async setAndInstallLocalPackageManager(info: PreparedPackageManagerInfo, {skipInstall = false}: {skipInstall?: boolean} = {}) {
     const {
       previousPackageManager,
     } = await specUtils.setLocalPackageManager(this.context.cwd, info);
 
+    if (skipInstall)
+      return 0;
+
     const command = this.context.engine.getPackageManagerSpecFor(info.locator).commands?.use ?? null;
     if (command === null)
       return 0;

sources/commands/Up.ts

@@ -1,4 +1,4 @@
-import {Command, UsageError}           from 'clipanion';
+import {Command, Option, UsageError}   from 'clipanion';
 import semverMajor                     from 'semver/functions/major.js';
 import semverValid                     from 'semver/functions/valid.js';
 import semverValidRange                from 'semver/ranges/valid.js';
@@ -19,6 +19,9 @@ export class UpCommand extends BaseCommand {
       of the package manager used in the local project, and update the project
       to use it.
 
+      With \`--skip-install\`, update the package manager without installing
+      the project's dependencies.
+
       Unlike \`corepack use\` this command doesn't take a package manager name
       nor a version range, as it will always select the latest available
       version from the same major line. Should you need to upgrade to a new
@@ -30,6 +33,10 @@ export class UpCommand extends BaseCommand {
     ]],
   });
 
+  skipInstall = Option.Boolean(`--skip-install`, false, {
+    description: `Skip installing the project's dependencies`,
+  });
+
   async execute() {
     const [descriptor] = await this.resolvePatternsToDescriptors({
       patterns: [],
@@ -52,6 +59,6 @@ export class UpCommand extends BaseCommand {
     this.context.stdout.write(`Installing ${highestVersion.name}@${highestVersion.reference} in the project...\n`);
 
     const packageManagerInfo = await this.context.engine.ensurePackageManager(highestVersion);
-    await this.setAndInstallLocalPackageManager(packageManagerInfo);
+    await this.setAndInstallLocalPackageManager(packageManagerInfo, {skipInstall: this.skipInstall});
   }
 }

sources/commands/Use.ts

@@ -13,6 +13,9 @@ export class UseCommand extends BaseCommand {
       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.
+
+      With \`--skip-install\`, update the package manager without installing
+      the project's dependencies.
     `,
     examples: [[
       `Configure the project to use the latest Yarn release`,
@@ -22,6 +25,10 @@ export class UseCommand extends BaseCommand {
 
   pattern = Option.String();
 
+  skipInstall = Option.Boolean(`--skip-install`, false, {
+    description: `Skip installing the project's dependencies`,
+  });
+
   async execute() {
     const [descriptor] = await this.resolvePatternsToDescriptors({
       patterns: [this.pattern],
@@ -34,6 +41,6 @@ export class UseCommand extends BaseCommand {
     this.context.stdout.write(`Installing ${resolved.name}@${resolved.reference} in the project...\n`);
 
     const packageManagerInfo = await this.context.engine.ensurePackageManager(resolved);
-    await this.setAndInstallLocalPackageManager(packageManagerInfo);
+    await this.setAndInstallLocalPackageManager(packageManagerInfo, {skipInstall: this.skipInstall});
   }
 }

tests/SkipInstall.test.ts

@@ -0,0 +1,74 @@
+import {npath, ppath, xfs}                from '@yarnpkg/fslib';
+import {beforeEach, describe, expect, it} from 'vitest';
+
+import {runCli}                           from './_runCli.ts';
+
+beforeEach(async () => {
+  const home = await xfs.mktempPromise();
+  process.env.COREPACK_HOME = npath.fromPortablePath(home);
+  process.env.COREPACK_DEFAULT_TO_LATEST = `0`;
+  process.env.AUTH_TYPE = `COREPACK_NPM_TOKEN`;
+  process.env.TEST_INTEGRITY = `valid`;
+
+  return async () => {
+    await xfs.removePromise(home, {recursive: true});
+  };
+});
+
+describe.each([`use`, `up`])(`%s --skip-install`, command => {
+  const args = command === `use` ? [`use`, `pnpm@latest`] : [`up`];
+
+  it.each([undefined, `--skip-install`, `--no-skip-install`])(`updates the manifest with option %j`, async option => {
+    const options = option ? [option] : [];
+    await xfs.mktempPromise(async cwd => {
+      const manifestPath = ppath.join(cwd, `package.json`);
+      await xfs.writeJsonPromise(manifestPath, {packageManager: `pnpm@1.0.0`});
+
+      await expect(runCli(cwd, [...args, ...options], true)).resolves.toEqual({
+        exitCode: 0,
+        stdout: `Installing pnpm@1.9998.9999 in the project...\n${options.includes(`--skip-install`) ? `` : `\npnpm: Hello from custom registry\n`}`,
+        stderr: ``,
+      });
+      await expect(xfs.readJsonPromise(manifestPath)).resolves.toMatchObject({
+        packageManager: expect.stringMatching(/^pnpm@1\.9998\.9999\+sha512\./),
+      });
+
+      // The package manager itself is installed even when dependencies aren't.
+      process.env.COREPACK_ENABLE_NETWORK = `0`;
+      await expect(runCli(cwd, [`pnpm`, `--version`], true)).resolves.toEqual({
+        exitCode: 0,
+        stdout: `pnpm: Hello from custom registry\n`,
+        stderr: ``,
+      });
+    });
+  });
+
+  it(`still verifies downloads before updating the manifest`, async () => {
+    process.env.TEST_INTEGRITY = `invalid_signature`;
+    await xfs.mktempPromise(async cwd => {
+      const manifestPath = ppath.join(cwd, `package.json`);
+      const manifest = {packageManager: `pnpm@1.0.0`};
+      await xfs.writeJsonPromise(manifestPath, manifest);
+
+      await expect(runCli(cwd, [...args, `--skip-install`], true)).resolves.toMatchObject({
+        exitCode: 1,
+        stderr: expect.stringContaining(`Signature does not match`),
+      });
+      await expect(xfs.readJsonPromise(manifestPath)).resolves.toEqual(manifest);
+    });
+  });
+});
+
+it(`use --skip-install still enforces devEngines constraints`, async () => {
+  await xfs.mktempPromise(async cwd => {
+    const manifestPath = ppath.join(cwd, `package.json`);
+    const manifest = {devEngines: {packageManager: {name: `pnpm`, version: `2.x`}}};
+    await xfs.writeJsonPromise(manifestPath, manifest);
+
+    await expect(runCli(cwd, [`use`, `pnpm@latest`, `--skip-install`], true)).resolves.toMatchObject({
+      exitCode: 1,
+      stdout: expect.stringContaining(`does not match the devEngines specification (pnpm@2.x)`),
+    });
+    await expect(xfs.readJsonPromise(manifestPath)).resolves.toEqual(manifest);
+  });
+});

tests/Use.test.ts

@@ -54,7 +54,7 @@ describe(`UseCommand`, () => {
         await expect(runCli(cwd, [`use`, `yarn@1.22.4`])).resolves.toMatchObject({
           exitCode: 1,
           stderr: ``,
-          stdout: `Installing yarn@1.22.4 in the project...\nUsage Error: The requested version of yarn@1.22.4+sha512.a1833b862fe52169bd6c2a033045a07df5bc6a23595c259e675fed1b2d035ab37abe6ce309720abb6636d68f03615054b6292dc0a70da31c8697fda228b50d18 does not match the devEngines specification (yarn@2.x)\n\n$ corepack use <pattern>\n`,
+          stdout: `Installing yarn@1.22.4 in the project...\nUsage Error: The requested version of yarn@1.22.4+sha512.a1833b862fe52169bd6c2a033045a07df5bc6a23595c259e675fed1b2d035ab37abe6ce309720abb6636d68f03615054b6292dc0a70da31c8697fda228b50d18 does not match the devEngines specification (yarn@2.x)\n\n$ corepack use [--skip-install] <pattern>\n`,
         });
 
         // Should accept setting to a compatible version: