Tsconfig extends resolution doesn't respect "tsconfig" key in package.json

[bgotink]

As part of resolving "extends" in tsconfig files, typescript looks for the "tsconfig" key in the package.json file. Esbuild instead looks for a few locations.

Our base tsconfig is called tsconfig.base.json as it's not meant to be picked up by typescript directly but via other tsconfigs that extend it. Our package.json includes "tsconfig": "./tsconfig.base.json", but esbuild doesn't pick that up.

https://github.com/microsoft/TypeScript/blob/4879087bef68e24ec2f7c98d83d70a88a5cc18c4/src/compiler/moduleNameResolver.ts#L377-L379

esbuild/internal/resolver/resolver.go

Line 1177 in ddfdfb8

filesToCheck := []string{r.fs.Join(join, "tsconfig.json"), join, join + ".json"}

[evanw]

Huh, today I learned. Where is that documented on https://www.typescriptlang.org/? I can't find any documentation about this. The only thing I found was this open issue which appears to be a request for a feature that doesn't exist.

[bgotink]

The only documentation I can find is in the typescript 3.2 release notes:

For each of those packages, TypeScript will first check whether package.json contains a "tsconfig" field, and if it does, TypeScript will try to load a configuration file from that field. If neither exists, TypeScript will try to read from a tsconfig.json at the root.

[evanw]

Thanks for the link. So it sounds like this only happens when you reference a package name via extends. In that case esbuild should check that package's package.json file for a tsconfig field. The relevant issue and PR is microsoft/TypeScript#18865 and microsoft/TypeScript#27348.