[clang][python][test] Move python binding tests to lit framework

As discussed in PR #142353, the current testsuite of the `clang` Python
bindings has several issues:

- It `libclang.so` cannot be loaded into `python` to run the testsuite, the
  whole `ninja check-all` aborts.
- The result of running the testsuite isn't report like the `lit`-based
  tests, rendering them almost invisible.
- The testsuite is disabled in a non-obvious way (`RUN_PYTHON_TESTS`) in
  `tests/CMakeLists.txt`, which again doesn't show up in the test results.

All these issues can be avoided by integrating the Python bindings tests
with `lit`, which is what this patch does:

- The actual test lives in `clang/test/bindings/python/bindings.sh` and is
  run by `lit`.
- The current `clang/bindings/python/tests` directory (minus the
  now-subperfluous `CMakeLists.txt`) is moved into the same directory.
- The check if `libclang` is loadable (originally from PR #142353) is now
  handled via a new `lit` feature, `libclang-loadable`.
- The various ways to disable the tests have been turned into `XFAIL`s as
  appropriate.  This isn't complete and not completely tested yet.

Tested on `sparc-sun-solaris2.11`, `sparcv9-sun-solaris2.11`,
`i386-pc-solaris2.11`, `amd64-pc-solaris2.11`, `i686-pc-linux-gnu`, and
`x86_64-pc-linux-gnu`.

Author: rorth

clang/CMakeLists.txt

@@ -530,7 +530,6 @@ if( CLANG_INCLUDE_TESTS )
     clang_unit_site_config=${CMAKE_CURRENT_BINARY_DIR}/test/Unit/lit.site.cfg
   )
   add_subdirectory(test)
-  add_subdirectory(bindings/python/tests)
 
   if(CLANG_BUILT_STANDALONE)
     umbrella_lit_testsuite_end(check-all)

clang/bindings/python/tests/CMakeLists.txt

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+# UNSUPPORTED: !libclang-loadable
+
+# Tests require libclang.so which is only built with LLVM_ENABLE_PIC=ON
+#
+# Covered by libclang-loadable, may need to augment test for lack of
+# libclang.so.
+
+# Do not try to run if libclang was built with sanitizers because
+# the sanitizer library will likely be loaded too late to perform
+# interception and will then fail.
+# We could use LD_PRELOAD/DYLD_INSERT_LIBRARIES but this isn't
+# portable so its easier just to not run the tests when building
+# with ASan.
+#
+# FIXME: Handle !LLVM_USE_SANITIZER = "".
+# lit.site.cfg.py has config.llvm_use_sanitizer = ""
+
+# Tests fail on Windows, and need someone knowledgeable to fix.
+# It's not clear whether it's a test or a valid binding problem.
+# XFAIL: target={{.*windows.*}}
+
+# The Python FFI interface is broken on AIX: https://bugs.python.org/issue38628.
+# XFAIL: target={{.*-aix.*}}
+
+# AArch64, Hexagon, and Sparc have known test failures that need to be
+# addressed.
+# SystemZ has broken Python/FFI interface:
+# https://reviews.llvm.org/D52840#1265716
+# XFAIL: target={{(aarch64|hexagon|sparc*|s390x)-.*}}
+
+# Tests will fail if cross-compiling for a different target, as tests will try
+# to use the host Python3_EXECUTABLE and make FFI calls to functions in target
+# libraries.
+#
+# FIXME: Consider a solution that allows better control over these tests in
+# a crosscompiling scenario. e.g. registering them with lit to allow them to
+# be explicitly skipped via appropriate LIT_ARGS, or adding a mechanism to
+# allow specifying a python interpreter compiled for the target that could
+# be executed using qemu-user.
+#
+# FIXME: Handle CMAKE_CROSSCOMPILING.
+# Again, might already be handled by libclang-loadable.
+
+# RUN: env PYTHONPATH=%S/../../../bindings/python \
+# RUN:   CLANG_LIBRARY_PATH=`llvm-config --libdir` \
+# RUN:   %python -m unittest discover -s %S/tests

clang/test/bindings/python/bindings.sh

@@ -0,0 +1,22 @@
+def is_libclang_loadable():
+    try:
+        sys.path.append(os.path.join(config.clang_src_dir, "bindings/python"))
+        from clang.cindex import Config
+        conf = Config()
+        Config.set_library_path(config.clang_lib_dir)
+        conf.lib
+        return True
+    except Exception as e:
+        # Benign error modes.
+        if "wrong ELF class: ELFCLASS32" in str(e):
+            return False
+        elif "No such file or directory" in str(e):
+            return False
+        # Unknown error modes.
+        else:
+            return True
+
+if is_libclang_loadable():
+    config.available_features.add("libclang-loadable")
+
+config.suffixes = ['.sh']