[libunwind] [test] Fix inferring source paths

[mgorny]

Summary

Fix two issues that caused libcxx source path not to be inferred
correctly when not specified explicitly:

1. get_lit_conf() uses default value only if the lit variable is set to None. Due to the mehod of substituting lit.site.cfg, they were "" rather than None when unset, effectively causing the default never to apply. Instead, use 'or' construct to use the default whenever get_lit_conf() returns a false value.

2. If os.path.join() is given a component starting with '/', it takes it to be an absolute path and ignores everything preceding it. Remove the slash to correctly append subdirectory.

With these two fixes, libunwind tests start working on NetBSD buildbot
again.

[mgorny]

Ping.

[krytarowski]

It is probably fine.. but I will defer review to lit/libc++ maintainers.

[mgorny]

Ping. Could somebody review this, please? It's blocking NetBSD buildbot for quite some time already.

[phosek]

LGTM

libunwind/test/libunwind/test/config.py

27 ↗

(On Diff #199799)

Can you use os.path.join(self.libunwind_src_root, '..', 'libcxx') to make it compatible with systems that don't use / as path separators?

[mgorny]

libunwind/test/libunwind/test/config.py

27 ↗

(On Diff #199799)

Good catch. Will do.

libunwind/trunk/test/libunwind/test/config.py

class Configuration(LibcxxConfiguration):
     def __init__(self, lit_config, config):
         super(Configuration, self).__init__(lit_config, config)
         self.libunwind_src_root = None
         self.libunwind_obj_root = None
         self.abi_library_path = None
         self.libcxx_src_root = None
 
     def configure_src_root(self):
-        self.libunwind_src_root = self.get_lit_conf(
-            'libunwind_src_root',
-            os.path.dirname(self.config.test_source_root))
-        self.libcxx_src_root = self.get_lit_conf(
-            'libcxx_src_root',
-            os.path.join(self.libunwind_src_root, '/../libcxx'))
+        self.libunwind_src_root = (self.get_lit_conf('libunwind_src_root')
+            or os.path.dirname(self.config.test_source_root))
+        self.libcxx_src_root = (self.get_lit_conf('libcxx_src_root')
+            or os.path.join(self.libunwind_src_root, '..', 'libcxx'))
 
     def configure_obj_root(self):
         self.libunwind_obj_root = self.get_lit_conf('libunwind_obj_root')
         super(Configuration, self).configure_obj_root()
 
     def has_cpp_feature(self, feature, required_value):
         return int(self.cxx.dumpMacros().get('__cpp_' + feature, 0)) >= required_value