[CMake] Add error to clarify that lldb requires libcxx

[jryans]

Summary

This adds a specific error message to clarify that lldb requires libcxx when
built together with clang on macOS. In addition, the lldb building docs are also
updated.

Fixes https://bugs.llvm.org/show_bug.cgi?id=41866

[JDevlieghere]

lldb/CMakeLists.txt

127 ↗

(On Diff #199346)

Should we check that LLVM_ENABLE_PROJECTS is not empty, for people that are still using the old layout?

[sgraenitz]

Thanks for adding this. Would it make sense to use LLVM_ENABLE_PROJECTS_USED? https://github.com/llvm/llvm-project/blob/a568222d/llvm/CMakeLists.txt#L128

BTW LLVM_ENABLE_PROJECTS can be "all" but LLVM should already have handled it at this point.

lldb/CMakeLists.txt

127 ↗

(On Diff #199346)

+1

[jryans]

Updated to support old project layout as well

[jryans]

Thanks all for the review! 😄

In D61877#1500981, @sgraenitz wrote:

Thanks for adding this. Would it make sense to use LLVM_ENABLE_PROJECTS_USED? https://github.com/llvm/llvm-project/blob/a568222d/llvm/CMakeLists.txt#L128

BTW LLVM_ENABLE_PROJECTS can be "all" but LLVM should already have handled it at this point.

LLVM_ENABLE_PROJECTS_USED seems to be about "what did we use last time", which felt confusing to test here, so I have avoided that so far.

In the updated version, I have changed to testing if(NOT TARGET cxx), which should cover all cases, including:

• LLVM_ENABLE_PROJECTS='clang;lldb;libcxx'
• LLVM_ENABLE_PROJECTS='all'
• Old layout

lldb/CMakeLists.txt

127 ↗

(On Diff #199346)

Ah yes, thanks for catching that! I have updated this to support the old layout as well.

[sgraenitz]

LGTM

[jryans]

Thanks for the review! 😄 I don't have commit access yet, so could you please commit this for me?

[sgraenitz]

Sure, will commit this on your behalf tomorrow. (If nothing else comes up.)

[jryans]

@sgraenitz Thanks for committing! 😄 I guess the original author info is lost for this one, but consider adding a "Patch by" line for future commits from those without access.

[sgraenitz]

Yes, sorry for that. I realized it after the commit was in. The commit I got from arc patch did have the original author information. It must have changed in git llvm push, probably because it's still going to SVN and then gets mirrored back to git. I missed this last detail.

consider adding a "Patch by" line for future commits from those without access.

Given that I do this about once a year, I hope we will have switched to git at this point ;-)

lldb/trunk/CMakeLists.txt

if(APPLE)
       # 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}")
         endif()
       else()
+        # We require libcxx for the test suite, so if we aren't building it,
+        # try to provide a helpful error about how to resolve the situation.
+        if(NOT TARGET cxx)
+          if(LLVM_ENABLE_PROJECTS STREQUAL "")
+            # If `LLVM_ENABLE_PROJECTS` is not being used (implying that we are
+            # using the old layout), suggest checking it out.
+            message(FATAL_ERROR
+              "LLDB test suite requires libc++, but it is currently disabled. "
+              "Please checkout `libcxx` in `llvm/projects` or disable tests "
+              "via `LLDB_INCLUDE_TESTS=OFF`.")
+          else()
+            # If `LLVM_ENABLE_PROJECTS` is being used, suggest adding it.
+            message(FATAL_ERROR
+              "LLDB test suite requires libc++, but it is currently disabled. "
+              "Please add `libcxx` to `LLVM_ENABLE_PROJECTS` or disable tests "
+              "via `LLDB_INCLUDE_TESTS=OFF`.")
+          endif()
+        endif()
         list(APPEND LLDB_TEST_DEPS cxx)
       endif()
     endif()
   endif()
 
   if(TARGET dsymutil)
     list(APPEND LLDB_TEST_DEPS dsymutil)
   endif()

lldb/trunk/docs/resources/build.rst

::
   > cmake $PATH_TO_LLVM -G Ninja
   > ninja lldb
 
 As noted in the "Building LLVM with CMake" page mentioned above, you can pass
 variables to cmake to change build behavior. If LLDB is built as a part of
 LLVM, then you can pass LLVM-specific CMake variables to cmake when building
 LLDB.
 
+If you are building both Clang and LLDB together, be sure to also add libc++,
+which is currently required for testing on macOS:
+
+::
+
+  > cmake -D LLVM_ENABLE_PROJECTS='clang;lldb;libcxx' $PATH_TO_LLVM -G Ninja
 
 Here are some commonly used LLDB-specific CMake variables:
 
 * ``LLDB_EXPORT_ALL_SYMBOLS:BOOL`` : Exports all symbols. Useful in conjunction
   with CMAKE_BUILD_TYPE=Debug.
 * ``LLDB_BUILD_FRAMEWORK:BOOL`` : Builds LLDB.framework as Xcode would
 * ``LLDB_CODESIGN_IDENTITY:STRING`` : Determines the codesign identity to use.
   An empty string means skip building debugserver to avoid codesigning.