fix: check for cpu and os constraints if the arrays are not empty

__tests__/commands/install/integration.js

@@ -793,11 +793,19 @@ test.concurrent('a subdependency of an optional dependency that fails should be
   });
 
 // disabled while fix is not merged
-test.skip('should not loose dependencies when installing with --production', 
-(): Promise<void> => {
-  // revealed https://github.com/yarnpkg/yarn/issues/2263
-  return runInstall({production: true}, 'prod-should-keep-subdeps', async (config) => {
-    // would be hoisted from gulp/vinyl-fs/glob-stream/minimatch/brace-expansion/balanced-match
-    assert.equal(await getPackageVersion(config, 'balanced-match'), '0.4.2');
+test.skip('should not loose dependencies when installing with --production',
+  (): Promise<void> => {
+    // revealed https://github.com/yarnpkg/yarn/issues/2263
+    return runInstall({production: true}, 'prod-should-keep-subdeps', async (config) => {
+      // would be hoisted from gulp/vinyl-fs/glob-stream/minimatch/brace-expansion/balanced-match
+      assert.equal(await getPackageVersion(config, 'balanced-match'), '0.4.2');
+    });
+  });
+
+// https://github.com/yarnpkg/yarn/issues/2470
+test.concurrent('a allows dependency with [] in os cpu requirements',
+  (): Promise<void> => {
+    return runInstall({}, 'empty-os', async (config) => {
+      assert(await fs.exists(path.join(config.cwd, 'node_modules', 'feed')));
+    });
   });
-});

__tests__/fixtures/install/empty-os/package.json

@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "feed": "0.3.0"
+  }
+}

__tests__/fixtures/install/empty-os/yarn.lock

@@ -0,0 +1,13 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+feed@0.3.0:
+  version "0.3.0"
+  resolved "https://registry.yarnpkg.com/feed/-/feed-0.3.0.tgz#65bcc4c9c57fde8e277faf4afff80c2d1d90e82d"
+  dependencies:
+    xml ">= 0.0.5"
+
+"xml@>= 0.0.5":
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/xml/-/xml-1.0.1.tgz#78ba72020029c5bc87b8a81a3cfcd74b4a2fc1e5"

src/package-compatibility.js

@@ -138,16 +138,20 @@ export default class PackageCompatibility {
       }
     };
 
-    if (!this.config.ignorePlatform && Array.isArray(info.os)) {
-      if (!PackageCompatibility.isValidPlatform(info.os)) {
-        pushError(this.reporter.lang('incompatibleOS', process.platform));
-      }
+    const invalidPlatform = !this.config.ignorePlatform &&
+      Array.isArray(info.os) &&
+      info.os.length > 0 &&
+      !PackageCompatibility.isValidPlatform(info.os);
+    if (invalidPlatform) {
+      pushError(this.reporter.lang('incompatibleOS', process.platform));
     }
 
-    if (!this.config.ignorePlatform && Array.isArray(info.cpu)) {
-      if (!PackageCompatibility.isValidArch(info.cpu)) {
-        pushError(this.reporter.lang('incompatibleCPU', process.arch));
-      }
+    const invalidCpu = !this.config.ignorePlatform &&
+      Array.isArray(info.cpu) &&
+      info.cpu.length > 0 &&
+      !PackageCompatibility.isValidArch(info.cpu);
+    if (invalidCpu) {
+      pushError(this.reporter.lang('incompatibleCPU', process.arch));
     }
 
     if (!this.ignoreEngines && typeof info.engines === 'object') {