Add ESLint

.eslintrc.yaml

@@ -0,0 +1,5 @@
+root: true
+extends:
+  - remcohaszing
+rules:
+  import/no-extraneous-dependencies: off

.github/workflows/ci.yaml

@@ -7,6 +7,16 @@ on:
     tags: ['*']
 
 jobs:
+  eslint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 20
+      - run: npm ci
+      - run: npx eslint .
+
   pack:
     runs-on: ubuntu-latest
     steps:
@@ -73,6 +83,7 @@ jobs:
   release:
     runs-on: ubuntu-latest
     needs:
+      - eslint
       - test
       - pack
       - prettier

index.ts

@@ -1,9 +1,13 @@
 import { resolve } from 'node:path'
-import { CompilerFunction, FrozenProcessor } from 'unified'
+
 // @ts-expect-error https://github.com/prettier/prettier-synchronized/pull/11
 import prettier from '@prettier/sync'
-import { Options } from 'prettier'
+import { type Options } from 'prettier'
+import { type CompilerFunction, type FrozenProcessor } from 'unified'
 
+/**
+ * @param options Options to pass to Prettier.
+ */
 function unifiedPrettier<Processor extends FrozenProcessor>(
   this: Processor,
   options?: Options | undefined
@@ -17,6 +21,7 @@ function unifiedPrettier<Processor extends FrozenProcessor>(
   this.Compiler = (tree, file) => {
     let content: unknown
     if (Compiler.prototype?.compile) {
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
       const compiler = new (Compiler as any)(tree, file)
       content = compiler.compile()
     } else {