fix: resolve tsconfig extends

closes #371

example/tsconfig.base.json

@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "useDefineForClassFields": false
+  }
+}

example/tsconfig.json

@@ -1,5 +1,3 @@
 {
-  "compilerOptions": {
-    "useDefineForClassFields": false
-  }
+  "extends": ["./tsconfig.base.json"]
 }

package.json

@@ -38,7 +38,7 @@
     "@rollup/pluginutils": "^5.0.4",
     "debug": "^4.3.4",
     "es-module-lexer": "^1.3.1",
-    "joycon": "^3.1.1"
+    "get-tsconfig": "^4.7.2"
   },
   "peerDependencies": {
     "esbuild": ">=0.18.0",

src/index.ts

@@ -150,9 +150,7 @@ export default ({
       }
 
       const tsconfigRaw =
-        tsconfig === false
-          ? undefined
-          : await getTsconfig(dirname(id), tsconfig)
+        tsconfig === false ? undefined : getTsconfig(tsconfig || id)
 
       const result = await transform(code, {
         loader,

src/tsconfig.ts

@@ -1,18 +1,9 @@
-import { readFile } from 'fs/promises'
-import JoyCon from 'joycon'
+import { getTsconfig as findTsconfig, TsConfigJsonResolved } from 'get-tsconfig'
 
-const joycon = new JoyCon()
+const cache = new Map<string, unknown>()
 
-joycon.addLoader({
-  test: /\.json$/,
-  load: (file) => readFile(file, 'utf8'),
-})
-
-export const getTsconfig = async (
-  cwd: string,
-  tsconfig?: string,
-): Promise<string> => {
-  // This call is cached
-  const { data } = await joycon.load([tsconfig || 'tsconfig.json'], cwd)
-  return data
+export function getTsconfig(
+  filename: string,
+): TsConfigJsonResolved | undefined {
+  return findTsconfig(filename, undefined, cache)?.config
 }