Throw for duplicate package names (closes #339)

Author: webpro

packages/knip/fixtures/dependencies/package.json

@@ -1,4 +1,5 @@
 {
+  "name": "@fixtures/dependencies",
   "scripts": {
     "start": "start-server",
     "test": "jest"

packages/knip/fixtures/plugins/ava/package.json

@@ -1,4 +1,5 @@
 {
+  "name": "@fixtures/ava",
   "ava": {
     "files": [
       "**/*.test.*"

packages/knip/fixtures/plugins/ava2/package.json

@@ -1,4 +1,5 @@
 {
+  "name": "@fixtures/ava2",
   "knip": {
     "ava": true
   }

packages/knip/fixtures/plugins/ava3/package.json

@@ -1,4 +1,5 @@
 {
+  "name": "@fixtures/ava3",
   "knip": {
     "ava": true
   }

packages/knip/fixtures/tsconfig-extends/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "@fixtures/typescript-extends",
+  "name": "@fixtures/tsconfig-extends",
   "workspaces": [
     "packages/*"
   ],

packages/knip/fixtures/tsconfig-extends/packages/frontend/package.json

@@ -1,4 +1,5 @@
 {
+  "name": "@tsconfig-extends/frontend",
   "dependencies": {
     "hastscript": "*"
   },

packages/knip/src/ConfigurationChief.ts

@@ -246,7 +246,7 @@ export class ConfigurationChief {
       .map(dir => join(this.cwd, dir));
 
     this.availableWorkspaceManifests = this.getAvailableWorkspaceManifests(this.availableWorkspaceDirs);
-    this.availableWorkspacePkgNames = new Set(this.availableWorkspaceManifests.map(w => w.manifest.name));
+    this.availableWorkspacePkgNames = this.getAvailableWorkspacePkgNames(this.availableWorkspaceManifests);
     this.workspacesGraph = createPkgGraph(this.availableWorkspaceManifests);
     this.enabledWorkspaces = this.getEnabledWorkspaces();
   }
@@ -316,6 +316,16 @@ export class ConfigurationChief {
     });
   }
 
+  private getAvailableWorkspacePkgNames(availableWorkspaceManifests: { dir: string; manifest: PackageJson }[]) {
+    const pkgNames = new Set<string>();
+    for (const { dir, manifest } of availableWorkspaceManifests) {
+      if (!manifest.name) throw new ConfigurationError(`Missing package name in ${join(dir, 'package.json')}`);
+      if (pkgNames.has(manifest.name)) throw new ConfigurationError(`Duplicate package name: ${manifest.name}`);
+      pkgNames.add(manifest.name);
+    }
+    return pkgNames;
+  }
+
   private getEnabledWorkspaces() {
     if (workspaceArg && !existsSync(workspaceArg)) {
       throw new ConfigurationError(`Directory does not exist: ${workspaceArg}`);