fix bin links for link: protocol (fixes #5876) (#5879)

__tests__/commands/install/bin-links.js

@@ -166,6 +166,15 @@ test('Only top level (after hoisting) bin links should be linked', (): Promise<v
   });
 });
 
+// fixes https://github.com/yarnpkg/yarn/issues/5876
+test('can use link protocol to install a package that would not be found via node module resolution', (): Promise<
+  void,
+> => {
+  return runInstall({binLinks: true}, {source: 'install-link-siblings', cwd: '/bar'}, async config => {
+    expect(await linkAt(config, 'node_modules', '.bin', 'standard')).toEqual('../standard/bin/cmd.js');
+  });
+});
+
 describe('with nohoist', () => {
   // address https://github.com/yarnpkg/yarn/issues/5487
   test('nohoist bin should be linked to its own local module', (): Promise<void> => {

__tests__/fixtures/install/install-link-siblings/bar/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "bar",
+  "version": "0.0.0",
+  "main": "index.js",
+  "dependencies": {
+    "foo": "link:../foo"
+  }
+}

__tests__/fixtures/install/install-link-siblings/foo/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "foo",
+  "version": "1.0.0",
+  "license": "MIT",
+  "dependencies": {
+    "standard": "8.4.0"
+  }
+}

src/package-linker.js

@@ -158,9 +158,14 @@ export default class PackageLinker {
     const realLocations = await Promise.all(ref.locations.map(loc => fs.realpath(loc)));
     realLocations.forEach(loc => allLocations.indexOf(loc) !== -1 || allLocations.push(loc));
 
-    const distancePairs = allLocations.map(loc => {
+    const locationBinLocPairs = allLocations.map(loc => [loc, binLoc]);
+    if (binLoc !== realBinLoc) {
+      locationBinLocPairs.push(...allLocations.map(loc => [loc, realBinLoc]));
+    }
+
+    const distancePairs = locationBinLocPairs.map(([loc, curBinLoc]) => {
       let distance = 0;
-      let curLoc = realBinLoc;
+      let curLoc = curBinLoc;
       let notFound = false;
 
       while (path.join(curLoc, ref.name) !== loc && path.join(curLoc, moduleFolder, ref.name) !== loc) {
@@ -180,6 +185,8 @@ export default class PackageLinker {
     const filteredDistancePairs: any = distancePairs.filter(d => d);
     (filteredDistancePairs: Array<[string, number]>);
 
+    invariant(filteredDistancePairs.length > 0, `could not find a copy of ${pkg.name} to link in ${binLoc}`);
+
     //get smallest distance from package location
     const minItem = filteredDistancePairs.reduce((min, cur) => {
       return cur[1] < min[1] ? cur : min;