dmpolukhin wrote:
> @dmpolukhin I am still confusing about the problem. I mean, why your previous
> patch will break the reproducer and why this patch can "fix" it? I feel the
> current patch is somewhat workaround. It's not your fault. The original codes
> are somewhat tricky already. But let's try to find methods to fix it more
> fundamentally.
I understand why my previous patch broke Google's reproducer I attached to this
PR. It happens because it deserializes eagerly lambda classes from the module
that should be chosen as a pattern for template instantiation (function
`CallbackUnaryHandler::RunHandler`). However code:
```
if (auto *RD = dyn_cast<CXXRecordDecl>(FD->getLexicalParent()))
if (RD->isDependentContext() && !RD->isThisDeclarationADefinition())
continue;
```
skips setting body for the function so it cannot be used as the pattern and
function body from different module is selected that now doesn't match the
lambda. As I wrote in #109167 for captured variables to work correctly we need
to make sure that enclosing function and lambda are coming from the same
module. This code in some sense doing similar thing it forces canonical
definition for the function defined inline within a class template be from the
same module as class template.
What I don't understand why clang cannot handle inline friend function coming
from one module but class template coming from another module. It works in
cases of member functions but friend inline function inside class template are
special in this sense and template instantiation cannot deduce return type. I
agree that my code is just reduces scope of previous hack to work only in cases
when it is really required (we have test case). Full solution should be one of
two (1) figure out why inline friend function and template have to be from the
same module, relax this requirement and remove this check completely or (2)
make sure that canonical decls for class template, inline functions and
potential lambdas are always chosen from the same module (my code from #109167
allows deserializing related decls from the same module if needed). I'm
exploring option (1) at the moment but template instantiation code is not very
familiar for me so it might take some time.
https://github.com/llvm/llvm-project/pull/111992
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