One thing that crossed my mind when I was looking at the TypeScript compiler. Was that it was parsing header "d.ts" files even though it wasn't used in source.

One thing that crossed my mind when I was looking at the TypeScript compiler. Was that it was parsing header "d.ts" files even though it wasn't used in source. Although, it had some references of a type in a small main function. Iirc, I think this was how most compilers did. The downside is that transitive deps can easily explode. Thus, compiling a super small main function can takes seconds. I did suggest a solution to just lazily parse/check symbols if they are encountered in source. Instead of when including a type, you have to parse all the transitive header files of the file that defines the type.