Tweak the plugin directory search (#5819)

* Update load-plugins.js

* Update load-plugins.js

* Adds a test

* Fixes lint

src/common/load-plugins.js

@@ -52,17 +52,23 @@ function loadPlugins(plugins, pluginSearchDirs) {
         pluginSearchDir
       );
 
-      if (!isDirectory(resolvedPluginSearchDir)) {
-        throw new Error(
-          `${pluginSearchDir} does not exist or is not a directory`
-        );
-      }
-
       const nodeModulesDir = path.resolve(
         resolvedPluginSearchDir,
         "node_modules"
       );
 
+      // In some fringe cases (ex: files "mounted" as virtual directories), the
+      // isDirectory(resolvedPluginSearchDir) check might be false even though
+      // the node_modules actually exists.
+      if (
+        !isDirectory(nodeModulesDir) &&
+        !isDirectory(resolvedPluginSearchDir)
+      ) {
+        throw new Error(
+          `${pluginSearchDir} does not exist or is not a directory`
+        );
+      }
+
       return findPluginsInNodeModules(nodeModulesDir).map(pluginName => ({
         name: pluginName,
         requirePath: resolve.sync(pluginName, {

tests_integration/__tests__/plugin-virtual-directory.js

@@ -0,0 +1,16 @@
+"use strict";
+
+const runPrettier = require("../runPrettier");
+
+describe("plugin search should not crash when prettier isn't inside a directory", () => {
+  runPrettier(
+    "plugins/virtualDirectory",
+    ["--stdin-filepath", "example.js", "--plugin-search-dir=."],
+    { input: "" }
+  ).test({
+    stdout: "",
+    stderr: "",
+    status: 0,
+    write: []
+  });
+});

tests_integration/runPrettier.js

@@ -55,6 +55,15 @@ function runPrettier(dir, args, options) {
     write.push({ filename, content });
   });
 
+  const origStatSync = fs.statSync;
+
+  jest.spyOn(fs, "statSync").mockImplementation(filename => {
+    if (path.basename(filename) === `virtualDirectory`) {
+      return origStatSync(path.join(__dirname, __filename));
+    }
+    return origStatSync(filename);
+  });
+
   const originalCwd = process.cwd();
   const originalArgv = process.argv;
   const originalExitCode = process.exitCode;