fix(unplugin-dts): correct module-resolution precedence in setModuleResolution (#486)

In setModuleResolution, `options.target ?? ts.ScriptTarget.ES5 >= 2` parsed as
`options.target ?? (ES5 >= 2)` = `options.target ?? false`, because `>=` binds
tighter than `??`. The resolved target was never compared: called in isolation
with an explicit low target (e.g. ES5), the helper picked ES2015 modules instead
of CommonJS.

Parenthesize as `(options.target ?? ts.ScriptTarget.ES5) >= ts.ScriptTarget.ES2015`
so the default is applied before the comparison, and use the enum rather than the
literal `2` for intent.

Scope: this is an internal-correctness fix to the helper. Its only caller in
Runtime spreads `fixedCompilerOptions` (target: ESNext) before calling it, so the
plugin itself never reaches the ES5 branch and behaviour is unchanged today; the
fix makes the helper correct if reused, or if that call path ever changes.

Adds three setModuleResolution cases, appended to the existing utils suite.

Author: DanMat

packages/unplugin-dts/src/core/utils.ts

@@ -416,7 +416,7 @@ export function setModuleResolution(options: CompilerOptions) {
   const module =
     typeof options.module === 'number'
       ? options.module
-      : (options.target ?? ts.ScriptTarget.ES5 >= 2)
+      : (options.target ?? ts.ScriptTarget.ES5) >= ts.ScriptTarget.ES2015
         ? ts.ModuleKind.ES2015
         : ts.ModuleKind.CommonJS
 

packages/unplugin-dts/tests/utils.spec.ts

@@ -2,6 +2,7 @@ import { normalize, resolve } from 'node:path'
 import { existsSync } from 'node:fs'
 import { describe, expect, it } from 'vitest'
 
+import ts from '../src/core/ts-loader.cjs'
 import {
   base64VLQEncode,
   ensureAbsolute,
@@ -18,6 +19,7 @@ import {
   parseTsAliases,
   queryPublicPath,
   resolveConfigDir,
+  setModuleResolution,
   toCapitalCase,
   transformDtsPath,
   transformSourceMappingURL,
@@ -492,3 +494,28 @@ export { testFn } from './comment';
     )
   })
 })
+
+describe('setModuleResolution', () => {
+  it('keeps an explicit moduleResolution', () => {
+    const options: ts.CompilerOptions = {
+      moduleResolution: ts.ModuleResolutionKind.NodeNext,
+    }
+    setModuleResolution(options)
+    expect(options.moduleResolution).toBe(ts.ModuleResolutionKind.NodeNext)
+  })
+
+  it('maps an ES5 target to CommonJS module resolution (Node10)', () => {
+    const options: ts.CompilerOptions = { target: ts.ScriptTarget.ES5 }
+    setModuleResolution(options)
+    expect(options.moduleResolution).toBe(ts.ModuleResolutionKind.Node10)
+  })
+
+  it('maps an ES2015+ target to ES2015 module resolution', () => {
+    const options: ts.CompilerOptions = { target: ts.ScriptTarget.ES2020 }
+    setModuleResolution(options)
+    const expected = ts.version.startsWith('5')
+      ? ts.ModuleResolutionKind.Bundler
+      : ts.ModuleResolutionKind.Classic
+    expect(options.moduleResolution).toBe(expected)
+  })
+})