feat: add pnpm dedupe --check (#6409)

.changeset/moody-jokes-destroy.md

@@ -0,0 +1,6 @@
+---
+"@pnpm/dedupe.issues-renderer": major
+"@pnpm/dedupe.check": major
+---
+
+Initial release.

.changeset/neat-cheetahs-turn.md

@@ -0,0 +1,6 @@
+---
+"@pnpm/plugin-commands-installation": minor
+pnpm: minor
+---
+
+Add `--check` flag to `pnpm dedupe`. No changes will be made to `node_modules` or the lockfile. Exits with a non-zero status code if changes are possible.

.changeset/poor-cobras-rule.md

@@ -0,0 +1,5 @@
+---
+"@pnpm/dedupe.types": major
+---
+
+Initial release.

.changeset/weak-maps-teach.md

@@ -0,0 +1,5 @@
+---
+"@pnpm/default-reporter": minor
+---
+
+Report errors from pnpm dedupe --check

cli/default-reporter/package.json

@@ -35,6 +35,8 @@
   "dependencies": {
     "@pnpm/config": "workspace:*",
     "@pnpm/core-loggers": "workspace:*",
+    "@pnpm/dedupe.issues-renderer": "workspace:*",
+    "@pnpm/dedupe.types": "workspace:*",
     "@pnpm/error": "workspace:*",
     "@pnpm/render-peer-issues": "workspace:*",
     "@pnpm/types": "workspace:*",

cli/default-reporter/src/reportError.ts

@@ -1,5 +1,7 @@
 import { type Config } from '@pnpm/config'
 import { type Log } from '@pnpm/core-loggers'
+import { renderDedupeCheckIssues } from '@pnpm/dedupe.issues-renderer'
+import { type DedupeCheckIssues } from '@pnpm/dedupe.types'
 import { type PnpmError } from '@pnpm/error'
 import { renderPeerIssues } from '@pnpm/render-peer-issues'
 import { type PeerDependencyIssuesByProjects } from '@pnpm/types'
@@ -66,6 +68,8 @@ function getErrorInfo (logObj: Log, config?: Config): {
       return reportEngineError(logObj as any) // eslint-disable-line @typescript-eslint/no-explicit-any
     case 'ERR_PNPM_PEER_DEP_ISSUES':
       return reportPeerDependencyIssuesError(err, logObj as any) // eslint-disable-line @typescript-eslint/no-explicit-any
+    case 'ERR_PNPM_DEDUPE_CHECK_ISSUES':
+      return reportDedupeCheckIssuesError(err, logObj as any) // eslint-disable-line @typescript-eslint/no-explicit-any
     case 'ERR_PNPM_FETCH_401':
     case 'ERR_PNPM_FETCH_403':
       return reportAuthError(err, logObj as any, config) // eslint-disable-line @typescript-eslint/no-explicit-any
@@ -414,3 +418,13 @@ function getHasMissingPeers (issuesByProjects: PeerDependencyIssuesByProjects) {
   return Object.values(issuesByProjects)
     .some((issues) => Object.values(issues.missing).flat().some(({ optional }) => !optional))
 }
+
+function reportDedupeCheckIssuesError (err: Error, msg: { dedupeCheckIssues: DedupeCheckIssues }) {
+  return {
+    title: err.message,
+    body: `\
+${renderDedupeCheckIssues(msg.dedupeCheckIssues)}
+Run ${chalk.yellow('pnpm dedupe')} to apply the changes above.
+`,
+  }
+}

cli/default-reporter/tsconfig.json

@@ -14,6 +14,12 @@
     {
       "path": "../../config/config"
     },
+    {
+      "path": "../../dedupe/issues-renderer"
+    },
+    {
+      "path": "../../dedupe/types"
+    },
     {
       "path": "../../packages/core-loggers"
     },

dedupe/check/README.md

@@ -0,0 +1,13 @@
+# @pnpm/dedupe.issues-renderer
+
+> Logic for "pnpm dedupe --check"
+
+## Installation
+
+```
+pnpm add @pnpm/dedupe.check
+```
+
+## License
+
+[MIT](LICENSE)

dedupe/check/jest.config.js

@@ -0,0 +1 @@
+module.exports = require('../../jest.config')

dedupe/check/package.json

@@ -0,0 +1,43 @@
+{
+  "name": "@pnpm/dedupe.check",
+  "version": "0.0.0",
+  "description": "Visualize pnpm dedupe --check issues.",
+  "bugs": {
+    "url": "https://github.com/pnpm/pnpm/issues"
+  },
+  "main": "lib/index.js",
+  "types": "lib/index.d.ts",
+  "files": [
+    "lib",
+    "!*.map"
+  ],
+  "keywords": [
+    "pnpm8"
+  ],
+  "license": "MIT",
+  "engines": {
+    "node": ">=16.14"
+  },
+  "repository": "https://github.com/pnpm/pnpm/blob/main/dedupe/check",
+  "scripts": {
+    "_test": "jest",
+    "test": "pnpm run compile && pnpm run _test",
+    "lint": "eslint \"src/**/*.ts\" \"test/**/*.ts\"",
+    "prepublishOnly": "pnpm run compile",
+    "compile": "tsc --build && pnpm run lint --fix"
+  },
+  "homepage": "https://github.com/pnpm/pnpm/blob/main/dedupe/check#readme",
+  "funding": "https://opencollective.com/pnpm",
+  "dependencies": {
+    "@pnpm/dedupe.types": "workspace:*",
+    "@pnpm/error": "workspace:*",
+    "@pnpm/lockfile-types": "workspace:*",
+    "@pnpm/types": "workspace:*"
+  },
+  "devDependencies": {
+    "@pnpm/dedupe.check": "workspace:*"
+  },
+  "exports": {
+    ".": "./lib/index.js"
+  }
+}

dedupe/check/src/DedupeCheckIssuesError.ts

@@ -0,0 +1,8 @@
+import { type DedupeCheckIssues } from '@pnpm/dedupe.types'
+import { PnpmError } from '@pnpm/error'
+
+export class DedupeCheckIssuesError extends PnpmError {
+  constructor (public dedupeCheckIssues: DedupeCheckIssues) {
+    super('DEDUPE_CHECK_ISSUES', 'Dedupe --check found changes to the lockfile')
+  }
+}

dedupe/check/src/dedupeDiffCheck.ts

@@ -0,0 +1,101 @@
+import { type ResolvedDependencies, type Lockfile } from '@pnpm/lockfile-types'
+import {
+  type ResolutionChangesByAlias,
+  type DedupeCheckIssues,
+  type SnapshotsChanges,
+} from '@pnpm/dedupe.types'
+import { DEPENDENCIES_FIELDS } from '@pnpm/types'
+import { DedupeCheckIssuesError } from './DedupeCheckIssuesError'
+
+const PACKAGE_SNAPSHOT_DEP_FIELDS = ['dependencies', 'optionalDependencies'] as const
+
+export function dedupeDiffCheck (prev: Lockfile, next: Lockfile): void {
+  const issues: DedupeCheckIssues = {
+    importerIssuesByImporterId: diffSnapshots(prev.importers, next.importers, DEPENDENCIES_FIELDS),
+    packageIssuesByDepPath: diffSnapshots(prev.packages ?? {}, next.packages ?? {}, PACKAGE_SNAPSHOT_DEP_FIELDS),
+  }
+
+  const changesCount =
+    countChangedSnapshots(issues.importerIssuesByImporterId) +
+    countChangedSnapshots(issues.packageIssuesByDepPath)
+
+  if (changesCount > 0) {
+    throw new DedupeCheckIssuesError(issues)
+  }
+}
+
+/**
+ * Get all the keys of an object T where the value extends some type U.
+ */
+type KeysOfValue<T, U> = KeyValueMatch<T, keyof T, U>
+type KeyValueMatch<T, K, U> = K extends keyof T
+  ? T[K] extends U ? K : never
+  : never
+
+/**
+ * Given a PackageSnapshot or ProjectSnapshot, returns the keys where values
+ * match ResolvedDependencies.
+ *
+ * Unfortunately the ResolvedDependencies interface is just
+ * Record<string,string> so this also matches the "engines" and "specifiers"
+ * block.
+ */
+type PossiblyResolvedDependenciesKeys<TSnapshot> = KeysOfValue<TSnapshot, ResolvedDependencies | undefined>
+
+function diffSnapshots<TSnapshot> (
+  prev: Record<string, TSnapshot>,
+  next: Record<string, TSnapshot>,
+  fields: ReadonlyArray<PossiblyResolvedDependenciesKeys<TSnapshot>>
+): SnapshotsChanges {
+  const removed: string[] = []
+  const updated: Record<string, ResolutionChangesByAlias> = {}
+
+  for (const [id, prevSnapshot] of Object.entries(prev)) {
+    const nextSnapshot = next[id]
+
+    if (nextSnapshot == null) {
+      removed.push(id)
+      continue
+    }
+
+    const updates = fields.reduce((acc: ResolutionChangesByAlias, dependencyField) => ({
+      ...acc,
+      ...getResolutionUpdates(prevSnapshot[dependencyField] ?? {}, nextSnapshot[dependencyField] ?? {}),
+    }), {})
+
+    if (Object.keys(updates).length > 0) {
+      updated[id] = updates
+    }
+  }
+
+  const added = Object.keys(next).filter(id => prev[id] == null)
+
+  return { added, removed, updated }
+}
+
+function getResolutionUpdates (prev: ResolvedDependencies, next: ResolvedDependencies): ResolutionChangesByAlias {
+  const updates: ResolutionChangesByAlias = {}
+
+  for (const [alias, prevResolution] of Object.entries(prev)) {
+    const nextResolution = next[alias]
+
+    if (prevResolution === nextResolution) {
+      continue
+    }
+
+    updates[alias] = nextResolution == null
+      ? { type: 'removed', prev: prevResolution }
+      : { type: 'updated', prev: prevResolution, next: nextResolution }
+  }
+
+  const newAliases = Object.entries(next).filter(([alias]) => prev[alias] == null)
+  for (const [alias, nextResolution] of newAliases) {
+    updates[alias] = { type: 'added', next: nextResolution }
+  }
+
+  return updates
+}
+
+export function countChangedSnapshots (snapshotChanges: SnapshotsChanges): number {
+  return snapshotChanges.added.length + snapshotChanges.removed.length + Object.keys(snapshotChanges.updated).length
+}

dedupe/check/src/index.ts

@@ -0,0 +1,2 @@
+export { dedupeDiffCheck, countChangedSnapshots } from './dedupeDiffCheck'
+export { DedupeCheckIssuesError } from './DedupeCheckIssuesError'

dedupe/check/test/dedupeDiffCheck.ts

@@ -0,0 +1,112 @@
+import { DedupeCheckIssuesError, dedupeDiffCheck } from '@pnpm/dedupe.check'
+import { type Lockfile } from '@pnpm/lockfile-types'
+
+describe('dedupeDiffCheck', () => {
+  it('should have no changes for same lockfile', () => {
+    const lockfile: Lockfile = {
+      importers: {
+        '.': {
+          specifiers: {},
+        },
+      },
+      lockfileVersion: 'testLockfileVersion',
+    }
+
+    expect(() => {
+      dedupeDiffCheck(lockfile, lockfile)
+    }).not.toThrow()
+  })
+
+  it('throws DedupeCheckIssuesError on changes', () => {
+    const before: Lockfile = {
+      importers: {
+        'packages/a': {
+          specifiers: {
+            'is-positive': '^3.0.0',
+          },
+          dependencies: {
+            'is-positive': '3.0.0',
+          },
+        },
+        'packages/b': {
+          specifiers: {
+            'is-positive': '^3.1.0',
+          },
+          dependencies: {
+            'is-positive': '3.1.0',
+          },
+        },
+      },
+      packages: {
+        '/is-positive@3.0.0': {
+          resolution: {
+            integrity: 'sha512-JDkaKp5jWv24ZaFuYDKTcBrC/wBOHdjhzLDkgrrkJD/j7KqqXsGcAkex336qHoOFEajMy7bYqUgm0KH9/MzQvw==',
+          },
+          engines: {
+            node: '>=0.10.0',
+          },
+        },
+        '/is-positive@3.1.0': {
+          resolution: {
+            integrity: 'sha1-hX21hKG6XRyymAUn/DtsQ103sP0=',
+          },
+          engines: {
+            node: '>=0.10.0',
+          },
+        },
+      },
+      lockfileVersion: 'testLockfileVersion',
+    }
+
+    const after: Lockfile = {
+      importers: {
+        'packages/a': {
+          specifiers: {
+            'is-positive': '^3.0.0',
+          },
+          dependencies: {
+            'is-positive': '3.1.0',
+          },
+        },
+        'packages/b': {
+          specifiers: {
+            'is-positive': '^3.1.0',
+          },
+          dependencies: {
+            'is-positive': '3.1.0',
+          },
+        },
+      },
+      packages: {
+        '/is-positive@3.1.0': {
+          resolution: {
+            integrity: 'sha1-hX21hKG6XRyymAUn/DtsQ103sP0=',
+          },
+          engines: {
+            node: '>=0.10.0',
+          },
+        },
+      },
+      lockfileVersion: 'testLockfileVersion',
+    }
+
+    expect(() => {
+      dedupeDiffCheck(before, after)
+    }).toThrow(new DedupeCheckIssuesError({
+      importerIssuesByImporterId: {
+        added: [],
+        removed: [],
+        updated: {
+          'packages/a': {
+            'is-positive': { type: 'updated', prev: '3.0.0', next: '3.1.0' },
+          },
+        },
+      },
+      packageIssuesByDepPath: {
+        added: [],
+        removed: ['/is-positive@3.0.0'],
+        updated: {},
+      },
+    }))
+  })
+})

dedupe/check/tsconfig.json

@@ -0,0 +1,26 @@
+{
+  "extends": "@pnpm/tsconfig",
+  "compilerOptions": {
+    "outDir": "lib",
+    "rootDir": "src"
+  },
+  "include": [
+    "src/**/*.ts",
+    "../../__typings__/**/*.d.ts"
+  ],
+  "references": [
+    {
+      "path": "../../lockfile/lockfile-types"
+    },
+    {
+      "path": "../../packages/error"
+    },
+    {
+      "path": "../../packages/types"
+    },
+    {
+      "path": "../types"
+    }
+  ],
+  "composite": true
+}

dedupe/check/tsconfig.lint.json

@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.json",
+  "include": [
+    "src/**/*.ts",
+    "test/**/*.ts",
+    "../../__typings__/**/*.d.ts"
+  ]
+}

dedupe/issues-renderer/README.md

@@ -0,0 +1,13 @@
+# @pnpm/dedupe.issues-renderer
+
+> Visualizes "pnpm dedupe --check" issues
+
+## Installation
+
+```
+pnpm add @pnpm/dedupe.issues-renderer
+```
+
+## License
+
+[MIT](LICENSE)

dedupe/issues-renderer/jest.config.js

@@ -0,0 +1 @@
+module.exports = require('../../jest.config')

dedupe/issues-renderer/package.json

@@ -0,0 +1,44 @@
+{
+  "name": "@pnpm/dedupe.issues-renderer",
+  "version": "0.0.0",
+  "description": "Visualize pnpm dedupe --check issues.",
+  "bugs": {
+    "url": "https://github.com/pnpm/pnpm/issues"
+  },
+  "main": "lib/index.js",
+  "types": "lib/index.d.ts",
+  "files": [
+    "lib",
+    "!*.map"
+  ],
+  "keywords": [
+    "pnpm8"
+  ],
+  "license": "MIT",
+  "engines": {
+    "node": ">=16.14"
+  },
+  "repository": "https://github.com/pnpm/pnpm/blob/main/dedupe/issues-renderer",
+  "scripts": {
+    "_test": "jest",
+    "test": "pnpm run compile && pnpm run _test",
+    "lint": "eslint \"src/**/*.ts\" \"test/**/*.ts\"",
+    "prepublishOnly": "pnpm run compile",
+    "compile": "tsc --build && pnpm run lint --fix"
+  },
+  "homepage": "https://github.com/pnpm/pnpm/blob/main/dedupe/issues-renderer#readme",
+  "funding": "https://opencollective.com/pnpm",
+  "dependencies": {
+    "@pnpm/dedupe.types": "workspace:*",
+    "archy": "^1.0.0",
+    "chalk": "^4.1.2"
+  },
+  "devDependencies": {
+    "@pnpm/dedupe.issues-renderer": "workspace:*",
+    "@types/archy": "0.0.32",
+    "strip-ansi": "^6.0.1"
+  },
+  "exports": {
+    ".": "./lib/index.js"
+  }
+}

dedupe/issues-renderer/src/index.ts

@@ -0,0 +1,56 @@
+import {
+  type ResolutionChange,
+  type DedupeCheckIssues,
+  type ResolutionChangesByAlias,
+  type SnapshotsChanges,
+} from '@pnpm/dedupe.types'
+import archy from 'archy'
+import chalk from 'chalk'
+
+export function renderDedupeCheckIssues (dedupeCheckIssues: DedupeCheckIssues) {
+  const importersReport = report(dedupeCheckIssues.importerIssuesByImporterId)
+  const packagesReport = report(dedupeCheckIssues.packageIssuesByDepPath)
+
+  const lines = []
+  if (importersReport !== '') {
+    lines.push(chalk.blueBright.underline('Importers'))
+    lines.push(importersReport)
+    lines.push('')
+  }
+  if (packagesReport !== '') {
+    lines.push(chalk.blueBright.underline('Packages'))
+    lines.push(packagesReport)
+    lines.push('')
+  }
+
+  return lines.join('\n')
+}
+
+/**
+ * Render snapshot changes. Expected to return an empty string for no changes.
+ */
+function report (snapshotChanges: SnapshotsChanges): string {
+  return [
+    ...Object.entries(snapshotChanges.updated).map(([alias, updates]) => archy(toArchy(alias, updates))),
+    ...snapshotChanges.added.map((id) => `${chalk.green('+')} ${id}`),
+    ...snapshotChanges.removed.map((id) => `${chalk.red('-')} ${id}`),
+  ].join('\n')
+}
+
+function toArchy (name: string, issue: ResolutionChangesByAlias): archy.Data {
+  return {
+    label: name,
+    nodes: Object.entries(issue).map(([alias, change]) => toArchyResolution(alias, change)),
+  }
+}
+
+function toArchyResolution (alias: string, change: ResolutionChange): archy.Data {
+  switch (change.type) {
+  case 'added':
+    return { label: `${chalk.green('+')} ${alias} ${chalk.gray(change.next)}` }
+  case 'removed':
+    return { label: `${chalk.red('-')} ${alias} ${chalk.gray(change.prev)}` }
+  case 'updated':
+    return { label: `${alias} ${chalk.red(change.prev)} ${chalk.gray('→')} ${chalk.green(change.next)}` }
+  }
+}

dedupe/issues-renderer/test/__snapshots__/index.ts.snap

@@ -0,0 +1,56 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`renderDedupeCheckIssues prints new importers and packages 1`] = `
+"Importers
+.
+└── + packages/a 0.0.0
+
++ packages/a
+
+Packages
+@types/tar-stream/2.2.2
+└── @types/node 14.18.42 → 18.15.11
+
+@types/tar/6.1.4
+└── @types/node 14.18.42 → 18.15.11
+
++ /@types/node/18.15.11
+- /@types/node/14.18.42
+"
+`;
+
+exports[`renderDedupeCheckIssues prints removed importer 1`] = `
+"Importers
+.
+└── @types/node 18.15.11 → 14.18.42
+
+- packages/a
+
+Packages
+@types/tar-stream/2.2.2
+└── @types/node 18.15.11 → 14.18.42
+
+@types/tar/6.1.4
+└── @types/node 18.15.11 → 14.18.42
+
++ /@types/node/14.18.42
+- /@types/node/18.15.11
+"
+`;
+
+exports[`renderDedupeCheckIssues prints removed packages and updated resolutions 1`] = `
+"Importers
+.
+└── @types/node 14.18.42 → 18.15.11
+
+
+Packages
+@types/tar-stream/2.2.2
+└── @types/node 14.18.42 → 18.15.11
+
+@types/tar/6.1.4
+└── @types/node 14.18.42 → 18.15.11
+
+- /@types/node/14.18.42
+"
+`;

dedupe/issues-renderer/test/index.ts

@@ -0,0 +1,85 @@
+import { renderDedupeCheckIssues } from '@pnpm/dedupe.issues-renderer'
+import stripAnsi from 'strip-ansi'
+
+describe('renderDedupeCheckIssues', () => {
+  test('prints removed packages and updated resolutions', () => {
+    expect(stripAnsi(renderDedupeCheckIssues({
+      importerIssuesByImporterId: {
+        added: [],
+        removed: [],
+        updated: {
+          '.': {
+            '@types/node': { type: 'updated', prev: '14.18.42', next: '18.15.11' },
+          },
+        },
+      },
+      packageIssuesByDepPath: {
+        added: [],
+        removed: ['/@types/node/14.18.42'],
+        updated: {
+          '@types/tar-stream/2.2.2': {
+            '@types/node': { type: 'updated', prev: '14.18.42', next: '18.15.11' },
+          },
+          '@types/tar/6.1.4': {
+            '@types/node': { type: 'updated', prev: '14.18.42', next: '18.15.11' },
+          },
+        },
+      },
+    }))).toMatchSnapshot()
+  })
+
+  test('prints new importers and packages', () => {
+    expect(stripAnsi(renderDedupeCheckIssues({
+      importerIssuesByImporterId: {
+        added: ['packages/a'],
+        removed: [],
+        updated: {
+          '.': {
+            'packages/a': { type: 'added', next: '0.0.0' },
+          },
+        },
+      },
+      packageIssuesByDepPath: {
+        added: [
+          // Suppose packages/a added a new @types/node dependency on 18.x.
+          '/@types/node/18.15.11',
+        ],
+        removed: ['/@types/node/14.18.42'],
+        updated: {
+          '@types/tar-stream/2.2.2': {
+            '@types/node': { type: 'updated', prev: '14.18.42', next: '18.15.11' },
+          },
+          '@types/tar/6.1.4': {
+            '@types/node': { type: 'updated', prev: '14.18.42', next: '18.15.11' },
+          },
+        },
+      },
+    }))).toMatchSnapshot()
+  })
+
+  test('prints removed importer', () => {
+    expect(stripAnsi(renderDedupeCheckIssues({
+      importerIssuesByImporterId: {
+        added: [],
+        removed: ['packages/a'],
+        updated: {
+          '.': {
+            '@types/node': { type: 'updated', prev: '18.15.11', next: '14.18.42' },
+          },
+        },
+      },
+      packageIssuesByDepPath: {
+        added: ['/@types/node/14.18.42'],
+        removed: ['/@types/node/18.15.11'],
+        updated: {
+          '@types/tar-stream/2.2.2': {
+            '@types/node': { type: 'updated', prev: '18.15.11', next: '14.18.42' },
+          },
+          '@types/tar/6.1.4': {
+            '@types/node': { type: 'updated', prev: '18.15.11', next: '14.18.42' },
+          },
+        },
+      },
+    }))).toMatchSnapshot()
+  })
+})

dedupe/issues-renderer/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "extends": "@pnpm/tsconfig",
+  "compilerOptions": {
+    "outDir": "lib",
+    "rootDir": "src"
+  },
+  "include": [
+    "src/**/*.ts",
+    "../../__typings__/**/*.d.ts"
+  ],
+  "references": [
+    {
+      "path": "../types"
+    }
+  ],
+  "composite": true
+}

dedupe/issues-renderer/tsconfig.lint.json

@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.json",
+  "include": [
+    "src/**/*.ts",
+    "test/**/*.ts",
+    "../../__typings__/**/*.d.ts"
+  ]
+}

dedupe/types/README.md

@@ -0,0 +1,13 @@
+# @pnpm/dedupe.types
+
+> Types for the pnpm dedupe command
+
+## Installation
+
+```
+pnpm add @pnpm/dedupe.types
+```
+
+## License
+
+[MIT](LICENSE)

dedupe/types/package.json

@@ -0,0 +1,36 @@
+{
+  "name": "@pnpm/dedupe.types",
+  "version": "0.0.0",
+  "description": "Types for the pnpm dedupe command",
+  "main": "lib/index.js",
+  "types": "lib/index.d.ts",
+  "exports": {
+    ".": "./lib/index.js"
+  },
+  "files": [
+    "lib",
+    "!*.map"
+  ],
+  "engines": {
+    "node": ">=16.14"
+  },
+  "scripts": {
+    "test": "pnpm run compile",
+    "prepublishOnly": "pnpm run compile",
+    "compile": "tsc --build && pnpm run lint --fix",
+    "lint": "eslint \"src/**/*.ts\""
+  },
+  "repository": "https://github.com/pnpm/pnpm/blob/main/dedupe/types",
+  "keywords": [
+    "pnpm8"
+  ],
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/pnpm/pnpm/issues"
+  },
+  "homepage": "https://github.com/pnpm/pnpm/blob/main/dedupe/types#readme",
+  "funding": "https://opencollective.com/pnpm",
+  "devDependencies": {
+    "@pnpm/dedupe.types": "workspace:*"
+  }
+}

dedupe/types/src/DedupeCheckIssues.ts

@@ -0,0 +1,30 @@
+export interface DedupeCheckIssues {
+  readonly importerIssuesByImporterId: SnapshotsChanges
+  readonly packageIssuesByDepPath: SnapshotsChanges
+}
+
+export interface SnapshotsChanges {
+  readonly added: readonly string[]
+  readonly removed: readonly string[]
+  readonly updated: Record<string, ResolutionChangesByAlias>
+}
+
+export type ResolutionChangesByAlias = Record<string, ResolutionChange>
+
+export type ResolutionChange = ResolutionAdded | ResolutionDeleted | ResolutionUpdated
+
+export interface ResolutionAdded {
+  readonly type: 'added'
+  readonly next: string
+}
+
+export interface ResolutionDeleted {
+  readonly type: 'removed'
+  readonly prev: string
+}
+
+export interface ResolutionUpdated {
+  readonly type: 'updated'
+  readonly prev: string
+  readonly next: string
+}

dedupe/types/src/index.ts

@@ -0,0 +1 @@
+export * from './DedupeCheckIssues'

dedupe/types/tsconfig.json

@@ -0,0 +1,13 @@
+{
+  "extends": "@pnpm/tsconfig",
+  "compilerOptions": {
+    "outDir": "lib",
+    "rootDir": "src"
+  },
+  "include": [
+    "src/**/*.ts",
+    "../../__typings__/**/*.d.ts"
+  ],
+  "references": [],
+  "composite": true
+}

dedupe/types/tsconfig.lint.json

@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.json",
+  "include": [
+    "src/**/*.ts",
+    "test/**/*.ts",
+    "../../__typings__/**/*.d.ts"
+  ]
+}

pkg-manager/plugin-commands-installation/package.json

@@ -65,6 +65,7 @@
     "@pnpm/config": "workspace:*",
     "@pnpm/constants": "workspace:*",
     "@pnpm/core": "workspace:*",
+    "@pnpm/dedupe.check": "workspace:*",
     "@pnpm/error": "workspace:*",
     "@pnpm/filter-workspace-packages": "workspace:*",
     "@pnpm/find-workspace-dir": "workspace:*",

pkg-manager/plugin-commands-installation/src/dedupe.ts

@@ -1,13 +1,19 @@
 import { docsUrl } from '@pnpm/cli-utils'
 import { UNIVERSAL_OPTIONS } from '@pnpm/common-cli-options-help'
+import { dedupeDiffCheck } from '@pnpm/dedupe.check'
 import renderHelp from 'render-help'
 import { type InstallCommandOptions } from './install'
 import { installDeps } from './installDeps'
 
-export const rcOptionsTypes = cliOptionsTypes
+export function rcOptionsTypes () {
+  return {}
+}
 
 export function cliOptionsTypes () {
-  return {}
+  return {
+    ...rcOptionsTypes(),
+    check: Boolean,
+  }
 }
 
 export const commandNames = ['dedupe']
@@ -20,6 +26,10 @@ export function help () {
         title: 'Options',
         list: [
           ...UNIVERSAL_OPTIONS,
+          {
+            description: 'Check if running dedupe would result in changes without installing packages or editing the lockfile. Exits with a non-zero status code if changes are possible.',
+            name: '--check',
+          },
         ],
       },
     ],
@@ -28,7 +38,11 @@ export function help () {
   })
 }
 
-export async function handler (opts: InstallCommandOptions) {
+export interface DedupeCommandOptions extends InstallCommandOptions {
+  readonly check?: boolean
+}
+
+export async function handler (opts: DedupeCommandOptions) {
   const include = {
     dependencies: opts.production !== false,
     devDependencies: opts.dev !== false,
@@ -39,5 +53,6 @@ export async function handler (opts: InstallCommandOptions) {
     dedupe: true,
     include,
     includeDirect: include,
+    lockfileCheck: opts.check ? dedupeDiffCheck : undefined,
   }, [])
 }

pkg-manager/plugin-commands-installation/test/dedupe.ts

@@ -1,4 +1,5 @@
 import path from 'path'
+import { DedupeCheckIssuesError } from '@pnpm/dedupe.check'
 import { readProjects } from '@pnpm/filter-workspace-packages'
 import { type Lockfile } from '@pnpm/lockfile-types'
 import { dedupe, install } from '@pnpm/plugin-commands-installation'
@@ -12,16 +13,64 @@ const f = fixtures(__dirname)
 
 describe('pnpm dedupe', () => {
   test('updates old resolutions from importers block and removes old packages', async () => {
-    const { originalLockfile, dedupedLockfile } = await testFixture('workspace-with-lockfile-dupes')
+    const { originalLockfile, dedupedLockfile, dedupeCheckError } = await testFixture('workspace-with-lockfile-dupes')
     // Many old packages should be deleted as result of deduping. See snapshot file for details.
     expect(diff(originalLockfile, dedupedLockfile, diffOptsForLockfile)).toMatchSnapshot()
+    expect(dedupeCheckError.dedupeCheckIssues).toEqual({
+      importerIssuesByImporterId: {
+        added: [],
+        removed: [],
+        updated: {
+          'packages/bar': {
+            ajv: {
+              next: '6.12.6',
+              prev: '6.10.2',
+              type: 'updated',
+            },
+          },
+        },
+      },
+      packageIssuesByDepPath: {
+        added: [],
+        removed: [
+          '/ajv/6.10.2',
+          '/fast-deep-equal/2.0.1',
+          '/fast-json-stable-stringify/2.0.0',
+          '/punycode/2.1.1',
+          '/uri-js/4.2.2',
+        ],
+        updated: {},
+      },
+    })
   })
 
   test('updates old resolutions from package block', async () => {
-    const { originalLockfile, dedupedLockfile } = await testFixture('workspace-with-lockfile-subdep-dupes')
+    const { originalLockfile, dedupedLockfile, dedupeCheckError } = await testFixture('workspace-with-lockfile-subdep-dupes')
     // This is a smaller scale test that should just update uri-js@4.2.2 to
     // punycode@2.3.0 and remove punycode@2.1.1. See snapshot file for details.
     expect(diff(originalLockfile, dedupedLockfile, diffOptsForLockfile)).toMatchSnapshot()
+    expect(dedupeCheckError.dedupeCheckIssues).toEqual({
+      importerIssuesByImporterId: {
+        added: [],
+        removed: [],
+        updated: {},
+      },
+      packageIssuesByDepPath: {
+        added: [],
+        removed: [
+          '/punycode/2.1.1',
+        ],
+        updated: {
+          '/uri-js/4.2.2': {
+            punycode: {
+              next: '2.3.0',
+              prev: '2.1.1',
+              type: 'updated',
+            },
+          },
+        },
+      },
+    })
   })
 })
 
@@ -67,6 +116,21 @@ async function testFixture (fixtureName: string) {
   await install.handler(opts)
   expect(await readProjectLockfile()).toEqual(originalLockfile)
 
+  let dedupeCheckError: DedupeCheckIssuesError | undefined
+  try {
+    await dedupe.handler({ ...opts, check: true })
+  } catch (err: unknown) {
+    expect(err).toBeInstanceOf(DedupeCheckIssuesError)
+    dedupeCheckError = err as DedupeCheckIssuesError
+  } finally {
+    // The dedupe check option should never change the lockfile.
+    expect(await readProjectLockfile()).toEqual(originalLockfile)
+  }
+
+  if (dedupeCheckError == null) {
+    throw new Error('Expected change report from pnpm dedupe --check')
+  }
+
   // The lockfile fixture has several packages that could be removed after
   // re-resolving versions.
   await dedupe.handler(opts)
@@ -88,5 +152,5 @@ async function testFixture (fixtureName: string) {
   await install.handler(opts)
   expect(await readProjectLockfile()).toEqual(dedupedLockfile)
 
-  return { originalLockfile, dedupedLockfile }
+  return { originalLockfile, dedupedLockfile, dedupeCheckError }
 }

pkg-manager/plugin-commands-installation/tsconfig.json

@@ -33,6 +33,9 @@
     {
       "path": "../../config/matcher"
     },
+    {
+      "path": "../../dedupe/check"
+    },
     {
       "path": "../../exec/plugin-commands-rebuild"
     },

pnpm-lock.yaml

@@ -433,6 +433,12 @@ importers:
       '@pnpm/core-loggers':
         specifier: workspace:*
         version: link:../../packages/core-loggers
+      '@pnpm/dedupe.issues-renderer':
+        specifier: workspace:*
+        version: link:../../dedupe/issues-renderer
+      '@pnpm/dedupe.types':
+        specifier: workspace:*
+        version: link:../../dedupe/types
       '@pnpm/error':
         specifier: workspace:*
         version: link:../../packages/error
@@ -746,6 +752,53 @@ importers:
         specifier: 1.3.31
         version: 1.3.31
 
+  dedupe/check:
+    dependencies:
+      '@pnpm/dedupe.types':
+        specifier: workspace:*
+        version: link:../types
+      '@pnpm/error':
+        specifier: workspace:*
+        version: link:../../packages/error
+      '@pnpm/lockfile-types':
+        specifier: workspace:*
+        version: link:../../lockfile/lockfile-types
+      '@pnpm/types':
+        specifier: workspace:*
+        version: link:../../packages/types
+    devDependencies:
+      '@pnpm/dedupe.check':
+        specifier: workspace:*
+        version: 'link:'
+
+  dedupe/issues-renderer:
+    dependencies:
+      '@pnpm/dedupe.types':
+        specifier: workspace:*
+        version: link:../types
+      archy:
+        specifier: ^1.0.0
+        version: 1.0.0
+      chalk:
+        specifier: ^4.1.2
+        version: 4.1.2
+    devDependencies:
+      '@pnpm/dedupe.issues-renderer':
+        specifier: workspace:*
+        version: 'link:'
+      '@types/archy':
+        specifier: 0.0.32
+        version: 0.0.32
+      strip-ansi:
+        specifier: ^6.0.1
+        version: 6.0.1
+
+  dedupe/types:
+    devDependencies:
+      '@pnpm/dedupe.types':
+        specifier: workspace:*
+        version: 'link:'
+
   env/node.fetcher:
     dependencies:
       '@pnpm/create-cafs-store':
@@ -3526,6 +3579,9 @@ importers:
       '@pnpm/core':
         specifier: workspace:*
         version: link:../core
+      '@pnpm/dedupe.check':
+        specifier: workspace:*
+        version: link:../../dedupe/check
       '@pnpm/error':
         specifier: workspace:*
         version: link:../../packages/error

pnpm-workspace.yaml

@@ -4,6 +4,7 @@ packages:
   - __utils__/*
   - cli/*
   - config/*
+  - dedupe/*
   - env/*
   - exec/*
   - fetching/*