The nounified frontend currently tries to construct dictionaries that
correspond to invalid instantiations (i.e., instantiations T[X] where
X does not satisfy the constraints specified on T's type parameter).
As a consequence, we may fail to find method expressions needed by the
dictionary.
The real fix for this is to avoid creating those dictionaries in the
first place, because they should never actually be needed at runtime.
But that seems scary for a backport: we've repeatedly attempted to
backport generics fixes, which have fixed one issue but introduced
another.
This CL is a minimally invasive solution to #54225, which avoids the
ICE by instead skipping emitting the invalid dictionary. If the
dictionary ends up not being needed (which I believe will always be
the case), then the linker's reachability analysis will simply ignore
its absence.
Or worst case, if the dictionary *is* reachable somehow, we've simply
turned an ICE into a link-time missing symbol failure. That's not
great for user experience, but it seems like a small trade off to
avoid risking breaking any other currently working code.
Updates #54225.
Change-Id: Ic379696079f4729b1dd6a66994a58cca50281a84
Reviewed-on: https://go-review.googlesource.com/c/go/+/429655
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
