[Bug] Fails to parse arrow function with generic argument

[DreierF]

ESBuild fails to parse a rather complex arrow function in my project.

Minimal example:

export const values = <V>(obj: Record<string, V>): V[] => Object.keys(obj).map(k => obj[k]);

Module build failed (from ./node_modules/esbuild-loader/src/index.js):
Error: Transform failed with 1 error:
.../src/test.ts:1:44: error: Expected ">" but found ","
    at failureErrorWithLog (.../node_modules/esbuild-loader/node_modules/esbuild/lib/main.js:303:15)
    at .../node_modules/esbuild-loader/node_modules/esbuild/lib/main.js:258:29
    at handleResponse (.../node_modules/esbuild-loader/node_modules/esbuild/lib/main.js:229:7)
    at Socket.readFromStdout (.../node_modules/esbuild-loader/node_modules/esbuild/lib/main.js:159:7)

[evanw]

This builds fine with esbuild when the file extension is .ts but fails with this error when the file extension is .tsx, so I'm assuming your file has a .tsx file extension:

example.tsx:1:44: error: Expected ">" but found ","
export const values = <V>(obj: Record<string, V>): V[] => Object.keys(obj).map(k => obj[k]);
                                            ^

If you try building this with the official TypeScript compiler, that also gives a similar error:

example.tsx:1:45 - error TS1003: Identifier expected.
export const values = <V>(obj: Record<string, V>): V[] => Object.keys(obj).map(k => obj[k]);
                                            ~

So this doesn't look like a bug with esbuild to me. The behavior of esbuild matches the behavior of the official TypeScript compiler. Perhaps you are using the incorrect file extension? Or perhaps you're using esbuild's API and incorrectly passing tsx as the loader instead of ts?

[DreierF]

Ah that makes sense!
I was actually using a ts file extension but had it wired up to options: { loader: 'tsx' } not considering the implications on parsing such constructs.

Thanks for the fast reply and sorry for the noise.