For a specific system (Linux, e.g):

What is the level of interoperability between the different D compilers; DMD, LDC, and GDC?

It appears each one has different benefits, and, different experimental features. Link-time optimization for LDC. GDC offering static analysis. I imagine there are more.

If I compile a D program with say, DMD, will every D library I include also have to use that same compiler (and compiler version) from scratch and need recompiled? Or is there a pre-defined ABI that makes everything compatible? If I use shared libraries instead of static linking, does the situation change?

Additionally, how do the debuggers GDB vs LLDB behave when compiled using a different brand D compiler? (e.g. demangling)

I have my own experiences but I'm not sure if there's clear cut "yes, definitely it's [this case]." answers out there.

On Friday, 7 July 2023 at 08:19:28 UTC, Chris Katko wrote:

Yes because of exception handling, the runtime functions are different.
You can try and you'll see linking error because of a missing "personality",
symbol.

From version to version of a same vendor that might work but as phobos is not binary compatible (ABI of functions is allowed to change from a version to another) this is a bit the lottery.

Mangling is identical for each vendor (this is a language spec) but as mentioned, EH functions are different so the breakpoint set to break on throw for DMD (i.e _d_throwdwarf) will not work for LDC (i.e _d_throw_exception)

So to conclude there's no interoperability