Add source mapping from IR

[jeaye]

Overview

When using a debugger, or viewing a stack trace, we want jank source information tied to our native code. This requires specifically emitting that information in the LLVM IR which we generate.

Steps

• Add a flag to enable source mapping (-g)
• When that flag is enabled, generate source information for all expressions
  • Start with just function definitions, then add fn calls, then work on let bindings, etc
• Verify this is working in GDB, LLDB, etc
• Verify this is working for stacktrace generation

References

The LLVM documentation for this is here: https://llvm.org/docs/SourceLevelDebugging.html

The LLVM build-your-own-language tutorial has a chapter on this: https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/LangImpl09.html

I would also use Clang, with LLVM IR output enabled, to see what it adds. For example:

❯ cat source-info.c
#include <stdio.h>

int main()
{
    printf("meow");
    return 0;
}

❯ clang -O0 -ggdb -S -emit-llvm -o - source-info.c
<inspect output>