Official C Challenge ①

Task:  Come up with an extension to the C programming language.  Provide a clear description of the extension, and a code sample that clearly shows what the extension is intended to do.

Prize:  (Winning criteria are not specified.)  The winner will have his extension featured in the C11 language standard.

My entry:  ... Sorry, I think C is perfect in every way already.

If I could add one language extension to C, it would be to compile a whole project at once instead of one file at a time, and not have to declare functions above where they are called.

Then you wouldn't need any header files. All identifiers are unique in C, so as long as the compiler can find it somewhere in your project, you never need to declare it. You don't need any kind of module system, any import declarations, nothing; as long as the compiler can see a function, you can call it.

And yes, this can be done incrementally. The compiler can just track dependencies, only recompiling those functions that change or that depend on a struct that has changed, and use incremental linking.