Fix unused @types DT dependencies (resolve #942)

packages/knip/fixtures/dependencies-types/index.ts

@@ -0,0 +1,5 @@
+import { meta } from '@eslint/js';
+import { Ajv } from 'ajv';
+
+console.log(meta);
+console.log(Ajv);

packages/knip/fixtures/dependencies-types/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "@fixtures/dependencies-types",
+  "dependencies": {
+    "@eslint/js": "^9.20.0",
+    "ajv": "^8.17.1"
+  },
+  "devDependencies": {
+    "@types/ajv": "^0.0.5",
+    "@types/eslint__js": "^8.42.3",
+    "@types/node": "^20.14.8"
+  }
+}

packages/knip/src/DependencyDeputy.ts

@@ -162,7 +162,7 @@ export class DependencyDeputy {
   }
 
   getHasTypesIncluded(workspaceName: string) {
-    return this.installedBinaries.get(workspaceName);
+    return this.hasTypesIncluded.get(workspaceName);
   }
 
   addReferencedDependency(workspaceName: string, packageName: string) {
@@ -214,7 +214,8 @@ export class DependencyDeputy {
 
     if (closestWorkspaceName || closestWorkspaceNameForTypes) {
       if (closestWorkspaceName) this.addReferencedDependency(closestWorkspaceName, packageName);
-      if (closestWorkspaceNameForTypes) this.addReferencedDependency(closestWorkspaceNameForTypes, typesPackageName);
+      if (closestWorkspaceNameForTypes && !this.hasTypesIncluded.get(closestWorkspaceNameForTypes)?.has(packageName))
+        this.addReferencedDependency(closestWorkspaceNameForTypes, typesPackageName);
       return true;
     }
     this.addReferencedDependency(workspace.name, packageName);
@@ -277,7 +278,7 @@ export class DependencyDeputy {
           if (IGNORE_DEFINITELY_TYPED.has(typedPackageName)) return true;
 
           // The `pkg` dependency already has types included, i.e. this `@types/pkg` is obsolete
-          if (hasTypesIncluded?.has(typedDependency)) return false;
+          if (hasTypesIncluded?.has(typedPackageName)) return false;
 
           // Ignore typed dependencies that have a host dependency that's referenced
           // Example: `next` (host) has `react-dom` and/or `@types/react-dom` (peer), peers can be ignored if host `next` is referenced
@@ -287,7 +288,7 @@ export class DependencyDeputy {
           ];
           if (hostDependencies.length) return !!hostDependencies.find(host => isReferencedDependency(host.name, true));
 
-          if (!referencedDependencies) return false;
+          if (!referencedDependencies?.has(dependency)) return false;
 
           return referencedDependencies.has(typedPackageName);
         }

packages/knip/test/definitely-typed.test.ts

@@ -14,6 +14,7 @@ test('Find unused DT @types', async () => {
   });
 
   assert(issues.devDependencies['package.json']['@types/unused']);
+  assert(issues.devDependencies['package.json']['@types/mocha']);
 
   assert.deepEqual(counters, {
     ...baseCounters,

packages/knip/test/dependencies-types.test.ts

@@ -0,0 +1,25 @@
+import { test } from 'bun:test';
+import assert from 'node:assert/strict';
+import { main } from '../src/index.js';
+import { resolve } from '../src/util/path.js';
+import baseArguments from './helpers/baseArguments.js';
+import baseCounters from './helpers/baseCounters.js';
+
+const cwd = resolve('fixtures/dependencies-types');
+
+test('Find unused @types dependencies', async () => {
+  const { issues, counters } = await main({
+    ...baseArguments,
+    cwd,
+  });
+
+  assert(issues.devDependencies['package.json']['@types/ajv']);
+  assert(issues.devDependencies['package.json']['@types/eslint__js']);
+
+  assert.deepEqual(counters, {
+    ...baseCounters,
+    devDependencies: 2,
+    processed: 1,
+    total: 1,
+  });
+});