[libcxx][test] Test visibility option before using it

[jsji]

Summary

On some platform visibility option might be unsupported. eg: AIX.
The error 'unsupported option '-fvisibility=hidden'' will prevent us
from running the intended test.

This patch propose that we set the substition according to compiler
support.

[jsji]

gentle ping...

[ldionne]

libcxx/test/libcxx/debug/extern-templates.sh.cpp

22

I checked and this test basically passes vacuously when we don't enforce hidden visibility. So instead, I would either mark the test as truly failing on AIX for lack of being able to control visibility (if that's the case -- IDK how AIX works when it comes to visibility):

// AIX doesn't have a notion of visibility, so this test is vacuous.
// UNSUPPORTED: whatever-triple-you-use-for-aix

Or, if there *is* a notion of visibility and it's simply that the compiler doesn't support -fvisibility=hidden, we should:

1. File a bug for the compiler to start supporting the option, and

2. Use this diff instead:

diff --git a/libcxx/test/libcxx/debug/extern-templates.sh.cpp b/libcxx/test/libcxx/debug/extern-templates.sh.cpp
index b43f4d10af5c..c635674a6606 100644
--- a/libcxx/test/libcxx/debug/extern-templates.sh.cpp
+++ b/libcxx/test/libcxx/debug/extern-templates.sh.cpp
@@ -21,12 +21,12 @@
 // option which clang doesn't accept on Windows.)
 // UNSUPPORTED: windows
 
-// XFAIL: LIBCXX-AIX-FIXME
-
-// RUN: %{cxx} %{flags} %{compile_flags} %s %{link_flags} -fPIC -DTU1 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -shared -o %t.lib
-// RUN: cd %T && %{cxx} %{flags} %{compile_flags} %s ./%basename_t.tmp.lib %{link_flags} -DTU2 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -o %t.exe
+// RUN: %{cxx} %{flags} %{compile_flags} %s %{link_flags} -fPIC -DTU1 -D_LIBCPP_DEBUG=1 -shared -o %t.lib
+// RUN: cd %T && %{cxx} %{flags} %{compile_flags} %s ./%basename_t.tmp.lib %{link_flags} -DTU2 -D_LIBCPP_DEBUG=1 -o %t.exe
 // RUN: %{exec} %t.exe
 
+#pragma GCC visibility push(hidden)
+
 #include <cassert>
 #include <cstdio>
 #include <sstream>

[jsji]

Yes, AIX clang hasn't supported visibility yet, we simply ignore all the visibility for now.

OK. Then I think we will leave this test as it is for now, we should be able to re-enable it once we support visibility later.

[daltenty]

We could pass the linker an export list with the desired visibility for the functions in test on AIX if we need the visibility for the test. This is likely what we'll have to do in other places in libc++ until clang on AIX has real visibility support.

libcxx/test/libcxx/debug/extern-templates.sh.cpp

 // UNSUPPORTED: libcpp-has-no-localization
 // UNSUPPORTED: cant-build-shared-library
 
 // This test relies on linking a shared library and then passing that shared
 // library as input when linking an executable; this is generally not supported
 // on Windows (GNU ld supports it, but MS link.exe and LLD don't) - one has to
 // use an import library instead. (Additionally, the test uses the -fPIC
 // option which clang doesn't accept on Windows.)
 // UNSUPPORTED: windows
 
-// XFAIL: LIBCXX-AIX-FIXME
-
-// RUN: %{cxx} %{flags} %{compile_flags} %s %{link_flags} -fPIC -DTU1 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -shared -o %t.lib
-// RUN: cd %T && %{cxx} %{flags} %{compile_flags} %s ./%basename_t.tmp.lib %{link_flags} -DTU2 -D_LIBCPP_DEBUG=1 -fvisibility=hidden -o %t.exe
+// RUN: %{cxx} %{flags} %{compile_flags} %s %{link_flags} -fPIC -DTU1 -D_LIBCPP_DEBUG=1 %{hiddenvisibility} -shared -o %t.lib
+// RUN: cd %T && %{cxx} %{flags} %{compile_flags} %s ./%basename_t.tmp.lib %{link_flags} -DTU2 -D_LIBCPP_DEBUG=1 %{hiddenvisibility} -o %t.exe
 // RUN: %{exec} %t.exe
 
 #include <cassert>
 #include <cstdio>
 #include <sstream>
 #include <string>
 
 std::string __attribute__((visibility("default"))) numToString(int x);

libcxx/utils/libcxx/test/features.py

Feature(name='broken-utf8-wchar-ctype',
           #include <locale.h>
           #include <wctype.h>
           int main(int, char**) {
             setlocale(LC_ALL, "en_US.UTF-8");
             return towlower(L'\\xDA') != L'\\xFA';
           }
           """)),
 
+  # Substitue the hidden visibility to empty string if unsupported.
+  Feature(name='hidden-visibility-if-support',
+          actions=lambda cfg:
+          [AddSubstitution('%{hiddenvisibility}', '-fvisibility=hidden')]
+          if hasCompileFlag(cfg, '-fvisibility=hidden') else
+          [AddSubstitution('%{hiddenvisibility}', '')]),
+
   # Whether Bash can run on the executor.
   # This is not always the case, for example when running on embedded systems.
   #
   # For the corner case of bash existing, but it being missing in the path
   # set in %{exec} as "--env PATH=one-single-dir", the executor does find
   # and executes bash, but bash then can't find any other common shell
   # utilities. Test executing "bash -c 'bash --version'" to see if bash
   # manages to find binaries to execute.