[lldb][cmake] Allow specifying custom libcxx for tests in standalone builds

[Michael137]

Summary

Standalone builds currently do not set the LLDB_HAS_LIBCXX,
LIBCXX_LIBRARY_DIR, LIBCXX_GENERATED_INCLUDE_DIR.
These are necessary for API tests with USE_LIBCPP to run against
a custom built libcxx. Thus on all buildbots using standalone builds
(most notably the public swift-ci), the API tests always run against
the libcxx headers in the system SDK.

This patch introduces a new cmake variable LLDB_TEST_LIBCXX_ROOT_DIR
that allows us to point the tests in standalone builds to a custom
libcxx directory.

Since the user can control the libcxx location we can hard error if
no such custom libcxx build exists.

[Michael137]

Outstanding question would be whether we want to mirror this change in utils/lldb-dotest/CMakeLists.txt. If so, we should probably extract all this libcxx logic into a common helper between the two.

[JDevlieghere]

lldb/test/CMakeLists.txt

142–143

If this is only necessary for the standalone build, then this should go in cmake/modules/LLDBStandalone.cmake.

[Michael137]

• Move variable into LLDBStandalone.cmake

[bulbazord]

LGTM!

lldb/cmake/modules/LLDBStandalone.cmake

 
 # We set LLVM_CMAKE_DIR so that GetSVN.cmake is found correctly when building SVNVersion.inc
 set(LLVM_CMAKE_DIR ${LLVM_CMAKE_DIR} CACHE PATH "Path to LLVM CMake modules")
 
 set(LLVM_MAIN_SRC_DIR ${LLVM_BUILD_MAIN_SRC_DIR} CACHE PATH "Path to LLVM source tree")
 set(LLVM_MAIN_INCLUDE_DIR ${LLVM_MAIN_INCLUDE_DIR} CACHE PATH "Path to llvm/include")
 set(LLVM_BINARY_DIR ${LLVM_BINARY_DIR} CACHE PATH "Path to LLVM build tree")
 
+set(LLDB_TEST_LIBCXX_ROOT_DIR "${LLVM_BINARY_DIR}" CACHE PATH
+    "The build root for libcxx. Used in standalone builds to point the API tests to a custom build of libcxx.")
+
 set(LLVM_LIT_ARGS "-sv" CACHE STRING "Default options for lit")
 
 set(lit_file_name "llvm-lit")
 if(CMAKE_HOST_WIN32 AND NOT CYGWIN)
   set(lit_file_name "${lit_file_name}.py")
 endif()
 
 function(append_configuration_directories input_dir output_dirs)

lldb/test/CMakeLists.txt

add_lldb_test_dependency(
     dsymutil
     llvm-strip
     not
     split-file
     yaml2obj
   )
 endif()
 
 # Add dependencies if we test with the in-tree clang.
 # This works with standalone builds as they import the clang target.
 if(TARGET clang)
   add_lldb_test_dependency(clang)
 
   # TestFullLtoStepping depends on LTO, and only runs when the compiler is clang.
   add_lldb_test_dependency(LTO)
 
   if (TARGET libcxx OR ("libcxx" IN_LIST LLVM_ENABLE_RUNTIMES))
     set(LLDB_HAS_LIBCXX ON)
if (TARGET compiler-rt OR "compiler-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
     set(LLDB_HAS_COMPILER_RT ON)
     add_lldb_test_dependency(compiler-rt)
   endif()
 
   if(APPLE AND NOT LLVM_TARGET_IS_CROSSCOMPILE_HOST)
     # FIXME: Standalone builds should import the cxx target as well.
     if(LLDB_BUILT_STANDALONE)
       # For now check that the include directory exists.
-      set(cxx_dir "${LLVM_BINARY_DIR}/include/c++")
-      if(NOT EXISTS ${cxx_dir})
-        message(WARNING "LLDB test suite requires libc++ in llvm/projects/libcxx or an existing build symlinked to ${cxx_dir}")
+      set(cxx_dir "${LLDB_TEST_LIBCXX_ROOT_DIR}/include/c++")
+      if(EXISTS ${cxx_dir})
+        # These variables make sure the API tests can run against a custom
+        # build of libcxx even for standalone builds.
+        set(LLDB_HAS_LIBCXX ON)
+        set(LIBCXX_LIBRARY_DIR "${LLDB_TEST_LIBCXX_ROOT_DIR}/lib${LIBCXX_LIBDIR_SUFFIX}")
+        set(LIBCXX_GENERATED_INCLUDE_DIR "${LLDB_TEST_LIBCXX_ROOT_DIR}/include/c++/v1")
+      else()
+        message(FATAL_ERROR
+            "Couldn't find libcxx build in '${LLDB_TEST_LIBCXX_ROOT_DIR}'. To run the "
+            "test-suite for a standalone LLDB build please build libcxx and point "
+            "LLDB_TEST_LIBCXX_ROOT_DIR to it.")
       endif()
     else()
       # We require libcxx for the test suite, so if we aren't building it,
       # provide a helpful error about how to resolve the situation.
       if(NOT LLDB_HAS_LIBCXX)
         message(FATAL_ERROR
           "LLDB test suite requires libc++, but it is currently disabled. "
           "Please add `libcxx` to `LLVM_ENABLE_RUNTIMES` or disable tests via "