Using the latest version 8.5.0 it seems tsup is not yet able to resolve the ${configDir} template variable in tsconfig files resulting in compile errors when issuing DTS files.

I've had no issue building the actual Javascript output but when emitting DTS files, there are TS2307 compiling errors related to paths still read with the template variable unreplaced.

I hacked line 1986 of index.js by adding options.dts.compilerOptions.paths = { '@/*': ['/home/path/to/my/project/src/*'] }; which solves the issue. So I'd be keen to investigate and submit a PR to fix this if this is really a bug or a missing feature.

Edit: after investigating a bit, it seems directly linked to evanw/esbuild#4050