TypeScript files are seen as JavaScript when tsup resolves types of an external package in certain conditions #1023
Description
If a package points a subpath export (exports: { "./a": "./a.ts" } in package.json) to a TypeScript file (“a.ts”: import {…} from "./b.ts"), and you use that package as a dependency, when you run tsup with dts: { resolve: true }:
the file (“a.ts”) itself is treated as TypeScript code, but TypeScript files (like “b.ts”) imported by the former file are treated as plain JavaScript codes.
If “a.ts” is set as the main export (exports: { ".": "./ts" }), everything works.
Reproduction
https://github.com/umajho/tsup-reproduction-dts-resolve-pnpm-workspace
in “packages/support-lib”:
// foo.ts:
export type Foo = "foo";
export const foo: Foo = "foo";
// bar-that-imports-foo.ts:
export * from "./foo";
// package.json:
{
// …
"exports": {
"./foo": "./foo.ts",
"./bar-that-imports-foo": "./bar-that-imports-foo.ts",
".": "./bar-that-imports-foo.ts"
}
}cd packages/lib-to-be-built
pnpm run build-foo-dts-resolve ⭕️
Importing from “support-lib” with the subpath “./foo”, and building the library using tsup with dts: { resolve: true }:
// lib-imports-foo.ts:
import { Foo, foo } from "@tsup-reproduction-dts-resolve-pnpm-workspace/support-lib/foo";
export const baz: Foo = foo;success
➜ lib-to-be-built git:(main) pnpm run build-foo-dts-resolve
> @tsup-reproduction-dts-resolve-pnpm-workspace/lib-to-be-built@1.0.0 build-foo-dts-resolve /private/tmp/test/packages/lib-to-be-built
> tsup --config tsup.foo-dts-resolve.config.ts
CLI Building entry: lib-imports-foo.ts
CLI Using tsconfig: tsconfig.json
CLI tsup v7.2.0
CLI Using tsup config: /private/tmp/test/packages/lib-to-be-built/tsup.foo-dts-resolve.config.ts
CLI Target: es2020
CLI Cleaning output folder
ESM Build start
ESM dist/lib-imports-foo.js 98.00 B
ESM ⚡️ Build success in 10ms
DTS Build start
DTS ⚡️ Build success in 474ms
DTS dist/lib-imports-foo.d.ts 60.00 B
pnpm run build-bar-using-main-dts-resolve ⭕️
Importing from “support-lib” with the main path, and building the library using tsup with dts: { resolve: true }:
// lib-imports-bar-using-main.ts:
import { Foo, foo } from "@tsup-reproduction-dts-resolve-pnpm-workspace/support-lib";
export const baz: Foo = foo;success
➜ lib-to-be-built git:(main) pnpm run build-bar-using-main-dts-resolve
> @tsup-reproduction-dts-resolve-pnpm-workspace/lib-to-be-built@1.0.0 build-bar-using-main-dts-resolve /private/tmp/test/packages/lib-to-be-built
> tsup --config tsup.bar-using-main-dts-resolve.config.ts
CLI Building entry: lib-imports-bar-using-main.ts
CLI Using tsconfig: tsconfig.json
CLI tsup v7.2.0
CLI Using tsup config: /private/tmp/test/packages/lib-to-be-built/tsup.bar-using-main-dts-resolve.config.ts
CLI Target: es2020
CLI Cleaning output folder
ESM Build start
ESM dist/lib-imports-bar-using-main.js 109.00 B
ESM ⚡️ Build success in 12ms
DTS Build start
DTS ⚡️ Build success in 453ms
DTS dist/lib-imports-bar-using-main.d.ts 60.00 B
pnpm run build-bar-dts-resolve ❌
Importing from “support-lib” with the subpath “./bar-that-imports-foo”, and building the library using tsup with dts: { resolve: true }:
// lib-imports-bar.ts:
import { Foo, foo } from "@tsup-reproduction-dts-resolve-pnpm-workspace/support-lib/bar-that-imports-foo";
export const baz: Foo = foo;failed
➜ lib-to-be-built git:(main) pnpm run build-bar-dts-resolve
> @tsup-reproduction-dts-resolve-pnpm-workspace/lib-to-be-built@1.0.0 build-bar-dts-resolve /private/tmp/test/packages/lib-to-be-built
> tsup --config tsup.bar-dts-resolve.config.ts
CLI Building entry: lib-imports-bar.ts
CLI Using tsconfig: tsconfig.json
CLI tsup v7.2.0
CLI Using tsup config: /private/tmp/test/packages/lib-to-be-built/tsup.bar-dts-resolve.config.ts
CLI Target: es2020
CLI Cleaning output folder
ESM Build start
ESM dist/lib-imports-bar.js 98.00 B
ESM ⚡️ Build success in 16ms
DTS Build start
Error parsing: /private/tmp/test/packages/support-lib/foo.ts:1:7
Error: error occured in dts build
at Worker.<anonymous> (/private/tmp/test/node_modules/.pnpm/tsup@7.2.0_typescript@5.2.2/node_modules/tsup/dist/index.js:2294:26)
at Worker.emit (node:events:511:28)
at MessagePort.<anonymous> (node:internal/worker:263:53)
at [nodejs.internal.kHybridDispatch] (node:internal/event_target:762:20)
at exports.emitMessage (node:internal/per_context/messageport:23:28)
DTS Build error
Unexpected token (Note that you need plugins to import files that are not JavaScript)
1: export type Foo = "foo";
^
2:
3: export const foo: Foo = "foo";
ELIFECYCLE Command failed with exit code 1.