[WIP] Skip already installed modules

src/package-linker.js

@@ -125,6 +125,7 @@ export default class PackageLinker {
 
     //
     const queue: Map<string, CopyQueueItem> = new Map();
+    const skipped: string[] = [];
     for (const [dest, {pkg, loc: src}] of flatTree) {
       const ref = pkg._reference;
       invariant(ref, 'expected package reference');
@@ -137,6 +138,15 @@ export default class PackageLinker {
         phantomFiles.push(path.join(dest, file));
       }
 
+      try {
+        const obj = await fs.readJson(path.join(dest, 'package.json'));
+        // If the package is installed and is the exact same version, skip
+        if(obj.version == ref.version) {
+          skipped.push(dest);
+          continue;
+        }
+      } catch(ex) {}
+
       queue.set(dest, {
         src,
         dest,
@@ -147,6 +157,9 @@ export default class PackageLinker {
         },
       });
     }
+    if(skipped.length > 0) {
+      this.reporter.lang('skippedInstalledModules', skipped.length);
+    }
 
     // keep track of all scoped paths to remove empty scopes after copy
     const scopedPaths = new Set();
@@ -183,6 +196,11 @@ export default class PackageLinker {
       }
     }
 
+    // skipped modules
+    for (const loc of skipped) {
+      possibleExtraneous.delete(loc);
+    }
+
     //
     let tick;
     await fs.copyBulk(Array.from(queue.values()), this.reporter, {

src/reporters/lang/en.js

@@ -148,6 +148,8 @@ const messages = {
   unmetPeer: 'Unmet peer dependency $0.',
   incorrectPeer: 'Incorrect peer dependency $0.',
 
+  skippedInstalledModules: 'Skipped $0 module(s) because they are already installed.',
+
   savedNewDependency: 'Saved 1 new dependency.',
   savedNewDependencies: 'Saved $0 new dependencies.',
 

yarn.lock

@@ -1,7 +1,5 @@
 # THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
 # yarn lockfile v1
-
-
 abab@^1.0.0:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/abab/-/abab-1.0.3.tgz#b81de5f7274ec4e756d797cd834f303642724e5d"
@@ -5409,3 +5407,4 @@ yargs@~3.27.0:
     os-locale "^1.4.0"
     window-size "^0.1.2"
     y18n "^3.2.0"
+