Here is the situation, AIUI:
1. We allow users to provide their own Monitors, which hook into
the synchronized(obj) statement.
2. These monitors' methods are unadorned (no nothrow/@nogc).
3. As a result, synchronized(obj) statements will not compile in
nothrow/@nogc code, because we can't know that the Monitor
implementation doesn't throw / use the GC.
4. As Matthias mentioned, fixing this was attempted before (by
making the Monitor methods `nothrow`). However, this broke code
(vibe.d specifically), as its implementation was actually not
`nothrow`: https://issues.dlang.org/show_bug.cgi?id=11216
This is a problem e.g. in Druntime code, because it currently
forces a lot of code that should be `nothrow` to not be annotated
as such, even when the synchronization objects used use the
standard D monitor implementation, which is actually `nothrow`.
So I guess the way forward here for the Druntime code is to
abandon the synchronized() statement and use locks directly?
