fix(compiler): correct module type for nodenext

packages/type-compiler/src/compiler.ts

@@ -94,7 +94,7 @@ import {
 } from './reflection-ast.js';
 import { SourceFile } from './ts-types.js';
 import { MappedModifier, ReflectionOp, TypeNumberBrand } from '@deepkit/type-spec';
-import { Resolver } from './resolver.js';
+import { readNearestPackageJson, Resolver } from './resolver.js';
 import { knownLibFilesForCompilerOptions } from '@typescript/vfs';
 import { debug, debug2 } from './debug.js';
 import { ConfigResolver, getConfigResolver, MatchResult, ReflectionConfig, ReflectionConfigCache, reflectionModeMatcher, ResolvedConfig } from './config.js';
@@ -1081,12 +1081,12 @@ export class ReflectionTransformer implements CustomTransformer {
         return this.sourceFile;
     }
 
-    protected getModuleType(): 'cjs' | 'esm' {
+    protected getModuleType(): 'esm' | 'cjs' {
         if (this.compilerOptions.module === ts.ModuleKind.Node16 || this.compilerOptions.module === ts.ModuleKind.NodeNext) {
-            if (this.sourceFile.impliedNodeFormat === ts.ModuleKind.ESNext) {
-                return 'esm';
-            }
-            return 'cjs';
+            if (this.sourceFile.fileName.endsWith('.mjs')) return 'esm';
+            if (this.sourceFile.fileName.endsWith('.cjs')) return 'cjs';
+            const pkg = readNearestPackageJson(this.sourceFile.fileName);
+            return pkg?.type === 'module' ? 'esm' : 'cjs';
         }
         return this.compilerOptions.module === ts.ModuleKind.CommonJS ? 'cjs' : 'esm';
     }

packages/type-compiler/src/resolver.ts

@@ -10,9 +10,32 @@ import {
     StringLiteral,
 } from 'typescript';
 import ts from 'typescript';
+import { parse, join, dirname } from 'node:path';
+import { existsSync, readFileSync } from 'node:fs';
 
 const { createSourceFile, resolveModuleName, isStringLiteral, JSDocParsingMode, ScriptTarget } = ts;
 
+const packageJsonCache: { dir: string, content: any | null }[] = [];
+
+export function readNearestPackageJson(filePath: string): any {
+    const cachedEntry = packageJsonCache
+        .filter(entry => filePath.startsWith(entry.dir))
+        .sort((a, b) => b.dir.length - a.dir.length)[0];
+
+    if (cachedEntry) return cachedEntry.content;
+
+    let dir = dirname(filePath);
+    while (dir !== parse(dir).root) {
+        const packageJsonPath = join(dir, 'package.json');
+        if (existsSync(packageJsonPath)) {
+            const content = JSON.parse(readFileSync(packageJsonPath, 'utf8'));
+            packageJsonCache.push({ dir, content });
+            return content;
+        }
+        dir = dirname(dir);
+    }
+}
+
 export function patternMatch(path: string, patterns: string[], base?: string): boolean {
     const include = patterns.filter(pattern => pattern[0] !== '!');
 

packages/type-compiler/src/ts-types.ts

@@ -15,6 +15,8 @@ export interface SourceFile extends TSSourceFile {
      */
     redirectInfo?: any;
 
+    fileName: string;
+
     scriptKind?: ScriptKind;
 
     externalModuleIndicator?: Node;