You need support for each language in the debugger, as symbols do not contain semantics. As users we for example know that `foo::bar` and `foo::baz` are methods of the same class `foo`, the debugger doesn't.
The problem with GCs is that pointers must contain some additional information (like an additional bit for mark and sweep), they are not "just" pointing to some memory. Without "knowing" that, the debugger cannot follow the pointer to its target. Or tricks with unboxed ints like making them 1 bit smaller and using the first 1 as a tag for "this is not a pointer, but an integer".
What do you mean? Why not? Clang PDBs for C++ work great. A GC isn’t particular disruptive to debug symbols afaik.