This relands https://github.com/llvm/llvm-project/pull/95963. It had to
be reverted because the `TestEarlyProcessLaunch.py` test was failing
on the incremental macOS bots. The test failed because it was relying on
expression log output from the ObjC introspection routines (but was
the expression was called from a C++ context). The relanded patch
simply ensures that the test runs the expressions as `ObjC` expressions.
When LLDB isn't able to find a `clang::Decl` in response
to a `FindExternalVisibleDeclsByName`, it will fall-back
to looking into the Objective-C runtime for that decl. This
ends up doing a lot of work which isn't necessary when we're
debugging a C++ program. This patch makes the ObjC lookup
conditional on the language that the ExpressionParser deduced
(which can be explicitly set using the `expr --language` option
or is set implicitly if we're stopped in an ObjC frame or a
C++ frame without debug-info).
rdar://96236519
This patch attempts to decouple C++ expression evaluation from
Objective-C support. We've previously enabled it by default (if a
runtime existed), but that meant we're opting into extra work we only
need to do for Objective-C, which complicates/slows down C++ expression
evaluation. Of course there's a valid use-case for this, which is
calling Objective-C APIs when stopped in C++ frames (which Objective-C++
developers might want to do). In those cases we should really prompt the
user to add the `expr --language objc++` flag. To accomodate a likely
frequent use-case where a user breaks in a system C++ library (without
debug-symbols) but their application is actually an Objective-C app, we
allow Objective-C support in C++ expressions if the current frame
doesn't have debug-info.
This fixes https://github.com/llvm/llvm-project/issues/75443 and allows
us to add more `LangOpts.ObjC` guards around the expression evaluator in
the future (e.g., we could avoid looking into the Objective-C runtime
during C++ expression evaluation, which we currently do
unconditionally).
Depends on https://github.com/llvm/llvm-project/pull/87657
