[libcxx] Always enable availability in the lit test suite.

[ldionne]

Summary

Running the tests without availability enabled doesn't really make sense:
availability annotations allow catching errors at compile-time instead
of link-time. Running the tests without availability enabled allows
confirming that a test breaks at link-time under some configuration,
but it is more useful to instead check that it should fail at compile-time.

Always enabling availability in the lit test suite will greatly simplify
XFAILs and troubleshooting of failing tests, which is currently a giant
pain because we have these two levels of possible failure: link-time and
compile-time.

[ldionne]

@mclow.lists This should fix the test failures you've been seeing. Would you please kindly test the patch on your system? I've tested the patch under several configurations but I'd like to make sure.

[ldionne]

I'm going to closely monitor potential CI failures. I think only CI on Apple platforms should be affected, but I'll keep an eye out.

libcxx/trunk/docs/DesignDocs/AvailabilityMarkup.rst

 
 * The `platform` parameter controls the deployment target. For example lit can
   be invoked with `--param=platform=macosx10.8`. Default is the current host.
 * The `use_system_cxx_lib` parameter indicates to use another library than the
   just built one. Invoking lit with `--param=use_system_cxx_lib=true` will run
   the test-suite against the host system library. Alternatively a path to the
   directory containing a specific prebuilt libc++ can be used, for example:
   `--param=use_system_cxx_lib=/path/to/macOS/10.8/`.
-* The `with_availability` boolean parameter enables the availability markup.
 
 Tests can be marked as XFAIL based on multiple features made available by lit:
 
 
-* if either `use_system_cxx_lib` or `with_availability` is passed to lit,
-  assuming `--param=platform=macosx10.8` is passed as well the following
-  features will be available:
+* if `use_system_cxx_lib` is passed to lit, assuming `--param=platform=macosx10.8`
+  is passed as well the following features will be available:
 
   - availability
   - availability=x86_64
   - availability=macosx
   - availability=x86_64-macosx
   - availability=x86_64-apple-macosx10.8
   - availability=macosx10.8
 

libcxx/trunk/utils/libcxx/test/config.py

class Configuration(object):
 
     def configure(self):
         self.configure_executor()
         self.configure_use_system_cxx_lib()
         self.configure_target_info()
         self.configure_cxx()
         self.configure_triple()
         self.configure_deployment()
-        self.configure_availability()
         self.configure_src_root()
         self.configure_obj_root()
         self.configure_cxx_stdlib_under_test()
         self.configure_cxx_library_root()
         self.configure_use_clang_verify()
         self.configure_use_thread_safety()
         self.configure_execute_external()
         self.configure_ccache()
def configure_use_system_cxx_lib(self):
             self.use_system_cxx_lib = True
         elif self.use_system_cxx_lib == 'false':
             self.use_system_cxx_lib = False
         elif self.use_system_cxx_lib:
             assert os.path.isdir(self.use_system_cxx_lib), "the specified use_system_cxx_lib parameter (%s) is not a valid directory" % self.use_system_cxx_lib
         self.lit_config.note(
             "inferred use_system_cxx_lib as: %r" % self.use_system_cxx_lib)
 
-    def configure_availability(self):
-        # See https://libcxx.llvm.org/docs/DesignDocs/AvailabilityMarkup.html
-        self.with_availability = self.get_lit_bool('with_availability', False)
-        self.lit_config.note(
-            "inferred with_availability as: %r" % self.with_availability)
-
     def configure_cxx_stdlib_under_test(self):
         self.cxx_stdlib_under_test = self.get_lit_conf(
             'cxx_stdlib_under_test', 'libc++')
         if self.cxx_stdlib_under_test not in \
                 ['libc++', 'libstdc++', 'msvc', 'cxx_default']:
             self.lit_config.fatal(
                 'unsupported value for "cxx_stdlib_under_test": %s'
                 % self.cxx_stdlib_under_test)
def configure_features(self):
                     'with_system_cxx_lib=%s' % component)
 
             # Add available features for more generic versions of the target
             # triple attached to  with_system_cxx_lib.
             if self.use_deployment:
                 self.add_deployment_feature('with_system_cxx_lib')
 
         # Configure the availability markup checks features.
-        if self.with_availability:
+        if self.use_deployment:
             self.config.available_features.add('availability_markup')
             self.add_deployment_feature('availability_markup')
 
-        if self.use_system_cxx_lib or self.with_availability:
             self.config.available_features.add('availability')
             self.add_deployment_feature('availability')
 
         if platform.system() == 'Darwin':
             self.config.available_features.add('apple-darwin')
 
         # Insert the platform name into the available features as a lower case.
         self.config.available_features.add(target_platform)
def configure_default_compile_flags(self):
                     ['-target', self.config.target_triple]):
                 self.lit_config.warning('use_target is true but -target is '\
                         'not supported by the compiler')
         if self.use_deployment:
             arch, name, version = self.config.deployment
             self.cxx.flags += ['-arch', arch]
             self.cxx.flags += ['-m' + name + '-version-min=' + version]
 
-        # Disable availability unless explicitly requested
-        if not self.with_availability:
-            self.cxx.flags += ['-D_LIBCPP_DISABLE_AVAILABILITY']
         # FIXME(EricWF): variant_size.pass.cpp requires a slightly larger
         # template depth with older Clang versions.
         self.cxx.addFlagIfSupported('-ftemplate-depth=270')
 
     def configure_compile_flags_header_includes(self):
         support_path = os.path.join(self.libcxx_src_root, 'test', 'support')
         self.configure_config_site_header()
         if self.cxx_stdlib_under_test != 'libstdc++' and \