--link-duplicates flag. Creates hardlinks to duplicate files in node_modules

__tests__/commands/install/integration-deduping.js

@@ -1,8 +1,10 @@
 /* @flow */
 
 import {getPackageVersion, runInstall} from '../_helpers.js';
+import * as fs from '../../../src/util/fs.js';
 
 const assert = require('assert');
+const path = require('path');
 
 jasmine.DEFAULT_TIMEOUT_INTERVAL = 120000;
 
@@ -201,3 +203,37 @@ test.concurrent('install should dedupe dependencies avoiding conflicts 9', (): P
     assert.equal(await getPackageVersion(config, 'run-async'), '0.1.0');
   });
 });
+
+test.concurrent('install should hardlink repeated dependencies', (): Promise<void> => {
+  // A@1
+  // B@1 -> A@2
+  // C@1 -> A@2 (this is hardlink to B@1->A@2)
+  return runInstall({linkDuplicates: true}, 'hardlink-repeated-dependencies', async (config) => {
+    const b_a = await fs.stat(path.join(
+      config.cwd,
+      'node_modules/b/node_modules/a/package.json',
+    ));
+    const c_a = await fs.stat(path.join(
+      config.cwd,
+      'node_modules/c/node_modules/a/package.json',
+    ));
+    assert.equal(b_a.ino, c_a.ino);
+  });
+});
+
+test.concurrent('install should not hardlink repeated dependencies if linkDuplicates=false', (): Promise<void> => {
+  // A@1
+  // B@1 -> A@2
+  // C@1 -> A@2
+  return runInstall({linkDuplicates: false}, 'hardlink-repeated-dependencies', async (config) => {
+    const b_a = await fs.stat(path.join(
+      config.cwd,
+      'node_modules/b/node_modules/a/package.json',
+    ));
+    const c_a = await fs.stat(path.join(
+      config.cwd,
+      'node_modules/c/node_modules/a/package.json',
+    ));
+    assert(b_a.ino != c_a.ino);
+  });
+});

__tests__/fixtures/install/hardlink-repeated-dependencies/deps/a-1/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "a",
+  "version": "1.0.0"
+}

__tests__/fixtures/install/hardlink-repeated-dependencies/deps/a-2/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "a",
+  "version": "2.0.0"
+}

__tests__/fixtures/install/hardlink-repeated-dependencies/deps/b-1/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "b",
+  "version": "1.0.0",
+  "dependencies": {
+    "a": "file:../a-2"
+  }
+}

__tests__/fixtures/install/hardlink-repeated-dependencies/deps/c-1/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "c",
+  "version": "1.0.0",
+  "dependencies": {
+    "a": "file:../a-2"
+  }
+}

__tests__/fixtures/install/hardlink-repeated-dependencies/package.json

@@ -0,0 +1,7 @@
+{
+  "dependencies": {
+    "a": "file:deps/a-1",
+    "b": "file:deps/b-1",
+    "c": "file:deps/c-1"
+  }
+}

src/cli/commands/install.js

@@ -50,11 +50,12 @@ export type IntegrityMatch = {
 
 type Flags = {
   // install
+  har: boolean,
   ignorePlatform: boolean,
   ignoreEngines: boolean,
   ignoreScripts: boolean,
   ignoreOptional: boolean,
-  har: boolean,
+  linkDuplicates: boolean,
   force: boolean,
   flat: boolean,
   lockfile: boolean,
@@ -128,6 +129,7 @@ function normalizeFlags(config: Config, rawFlags: Object): Flags {
     pureLockfile: !!rawFlags.pureLockfile,
     skipIntegrity: !!rawFlags.skipIntegrity,
     frozenLockfile: !!rawFlags.frozenLockfile,
+    linkDuplicates: !!rawFlags.linkDuplicates,
 
     // add
     peer: !!rawFlags.peer,
@@ -397,7 +399,7 @@ export class Install {
       const loc = await this.getIntegrityHashLocation();
       await fs.unlink(loc);
       this.reporter.step(curr, total, this.reporter.lang('linkingDependencies'), emoji.get('link'));
-      await this.linker.init(patterns);
+      await this.linker.init(patterns, this.flags.linkDuplicates);
     });
 
     steps.push(async (curr: number, total: number) => {

src/cli/index.js

@@ -64,6 +64,7 @@ commander.option('--prod, --production [prod]', '');
 commander.option('--no-lockfile', "don't read or generate a lockfile");
 commander.option('--pure-lockfile', "don't generate a lockfile");
 commander.option('--frozen-lockfile', "don't generate a lockfile and fail if an update is needed");
+commander.option('--link-duplicates', 'create hardlinks to the repeated modules in node_modules');
 commander.option('--global-folder <path>', '');
 commander.option(
   '--modules-folder <path>',

src/package-linker.js

@@ -112,7 +112,7 @@ export default class PackageLinker {
     return Promise.resolve(hoister.init());
   }
 
-  async copyModules(patterns: Array<string>): Promise<void> {
+  async copyModules(patterns: Array<string>, linkDuplicates: boolean): Promise<void> {
     let flatTree = await this.getFlatHoistedTree(patterns);
 
     // sorted tree makes file creation and copying not to interfere with each other
@@ -121,10 +121,13 @@ export default class PackageLinker {
     });
 
     // list of artifacts in modules to remove from extraneous removal
-    const phantomFiles = [];
+    const artifactFiles = [];
 
-    //
-    const queue: Map<string, CopyQueueItem> = new Map();
+    const copyQueue: Map<string, CopyQueueItem> = new Map();
+    const hardlinkQueue: Map<string, CopyQueueItem> = new Map();
+    const hardlinksEnabled = linkDuplicates && await fs.hardlinksWork(this.config.cwd);
+
+    const copiedSrcs: Map<string, string> = new Map();
     for (const [dest, {pkg, loc: src}] of flatTree) {
       const ref = pkg._reference;
       invariant(ref, 'expected package reference');
@@ -134,18 +137,34 @@ export default class PackageLinker {
       // extraneous
       const metadata = await this.config.readPackageMetadata(src);
       for (const file of metadata.artifacts) {
-        phantomFiles.push(path.join(dest, file));
+        artifactFiles.push(path.join(dest, file));
       }
 
-      queue.set(dest, {
-        src,
-        dest,
-        onFresh() {
-          if (ref) {
-            ref.setFresh(true);
-          }
-        },
-      });
+      const copiedDest = copiedSrcs.get(src);
+      if (!copiedDest) {
+        if (hardlinksEnabled) {
+          copiedSrcs.set(src, dest);
+        }
+        copyQueue.set(dest, {
+          src,
+          dest,
+          onFresh() {
+            if (ref) {
+              ref.setFresh(true);
+            }
+          },
+        });
+      } else {
+        hardlinkQueue.set(dest, {
+          src: copiedDest,
+          dest,
+          onFresh() {
+            if (ref) {
+              ref.setFresh(true);
+            }
+          },
+        });
+      }
     }
 
     // keep track of all scoped paths to remove empty scopes after copy
@@ -179,15 +198,15 @@ export default class PackageLinker {
       const stat = await fs.lstat(loc);
       if (stat.isSymbolicLink()) {
         possibleExtraneous.delete(loc);
-        queue.delete(loc);
+        copyQueue.delete(loc);
       }
     }
 
     //
     let tick;
-    await fs.copyBulk(Array.from(queue.values()), this.reporter, {
+    await fs.copyBulk(Array.from(copyQueue.values()), this.reporter, {
       possibleExtraneous,
-      phantomFiles,
+      artifactFiles,
 
       ignoreBasenames: [
         constants.METADATA_FILENAME,
@@ -204,6 +223,28 @@ export default class PackageLinker {
         }
       },
     });
+    await fs.hardlinkBulk(Array.from(hardlinkQueue.values()), this.reporter, {
+      possibleExtraneous,
+      artifactFiles,
+
+      onStart: (num: number) => {
+        tick = this.reporter.progress(num);
+      },
+
+      onProgress(src: string) {
+        if (tick) {
+          tick(src);
+        }
+      },
+    });
+
+    // remove all extraneous files that weren't in the tree
+    for (const loc of possibleExtraneous) {
+      this.reporter.verbose(
+        this.reporter.lang('verboseFileRemoveExtraneous', loc),
+      );
+      await fs.unlink(loc);
+    }
 
     // remove any empty scoped directories
     for (const scopedPath of scopedPaths) {
@@ -287,9 +328,9 @@ export default class PackageLinker {
     return range === '*' || semver.satisfies(version, range, this.config.looseSemver);
   }
 
-  async init(patterns: Array<string>): Promise<void> {
+  async init(patterns: Array<string>, linkDuplicates: boolean): Promise<void> {
     this.resolvePeerModules();
-    await this.copyModules(patterns);
+    await this.copyModules(patterns, linkDuplicates);
     await this.saveAll(patterns);
   }
 

src/reporters/lang/en.js

@@ -33,9 +33,11 @@ const messages = {
   manifestDirectoryNotFound: 'Unable to read $0 directory of module $1',
 
   verboseFileCopy: 'Copying $0 to $1.',
+  verboseFileLink: 'Creating hardlink at $0 to $1.',
   verboseFileSymlink: 'Creating symlink at $0 to $1.',
   verboseFileSkip: 'Skipping copying of file $0 as the file at $1 is the same size ($2) and mtime ($3).',
   verboseFileSkipSymlink: 'Skipping copying of $0 as the file at $1 is the same symlink ($2).',
+  verboseFileSkipHardlink: 'Skipping copying of $0 as the file at $1 is the same hardlink ($2).',
   verboseFileRemoveExtraneous: 'Removing extraneous file $0.',
   verboseFilePhantomExtraneous: "File $0 would be marked as extraneous but has been removed as it's listed as a phantom file.",
   verboseFileFolder: 'Creating directory $0.',