Reapplication of 7339c0f782d5c70e0928f8991b0c05338a90c84c with a fix
for a crash involving arrays without a size expression.
Clang supports VLAs in C++ as an extension, but we currently only warn
on their use when you pass -Wvla, -Wvla-extension, or -pedantic.
However, VLAs as they're expressed in C have been considered by WG21
and rejected, are easy to use accidentally to the surprise of users
(e.g., https://ddanilov.me/default-non-standard-features/), and they
have potential security implications beyond constant-size arrays
(https://wiki.sei.cmu.edu/confluence/display/c/ARR32-C.+Ensure+size+arguments+for+variable+length+arrays+are+in+a+valid+range).
C++ users should strongly consider using other functionality such as
std::vector instead.
This seems like sufficiently compelling evidence to warn users about
VLA use by default in C++ modes. This patch enables the -Wvla-extension
diagnostic group in C++ language modes by default, and adds the warning
group to -Wall in GNU++ language modes. The warning is still opt-in in
C language modes, where support for VLAs is somewhat less surprising to
users.
RFC: https://discourse.llvm.org/t/rfc-diagnosing-use-of-vlas-in-c/73109
Fixes https://github.com/llvm/llvm-project/issues/62836
Differential Revision: https://reviews.llvm.org/D156565
Based on post-commit review discussion on
2bd84938470bf2e337801faafb8a67710f46429d with Richard Smith.
Other uses of forcing HasEmptyPlaceHolder to false seem OK to me -
they're all around pointer/reference types where the pointer/reference
token will appear at the rightmost side of the left side of the type
name, so they make nested types (eg: the "int" in "int *") behave as
though there is a non-empty placeholder (because the "*" is essentially
the placeholder as far as the "int" is concerned).
This was originally committed in 277623f4d5a672d707390e2c3eaf30a9eb4b075c
Reverted in f9ad1d1c775a8e264bebc15d75e0c6e5c20eefc7 due to breakages
outside of clang - lldb seems to have some strange/strong dependence on
"char [N]" versus "char[N]" when printing strings (not due to that name
appearing in DWARF, but probably due to using clang to stringify type
names) that'll need to be addressed, plus a few other odds and ends in
other subprojects (clang-tools-extra, compiler-rt, etc).
Looks like lldb has some issues with this - somehow it causes lldb to
treat a "char[N]" type as an array of chars (prints them out
individually) but a "char [N]" is printed as a string. (even though the
DWARF doesn't have this string in it - it's something to do with the
string lldb generates for itself using clang)
This reverts commit 277623f4d5a672d707390e2c3eaf30a9eb4b075c.
Based on post-commit review discussion on
2bd84938470bf2e337801faafb8a67710f46429d with Richard Smith.
Other uses of forcing HasEmptyPlaceHolder to false seem OK to me -
they're all around pointer/reference types where the pointer/reference
token will appear at the rightmost side of the left side of the type
name, so they make nested types (eg: the "int" in "int *") behave as
though there is a non-empty placeholder (because the "*" is essentially
the placeholder as far as the "int" is concerned).
