Fix include path bugs from libclang on OSX with llvm 10 (#1162)

On OSX, with LLVM 10, it seems that there can be a double linkage of
the libc++ that is built with llvm and the one in /usr/lib.

This leads to a very subtle problem where oslc's use of libclang for
preprocessing is unable to find included files when there are multiple
include search paths (!), unless you have the llvm lib directory first
in your DYLD_LIBRARY_PATH. That is obviously too brittle a fix.

Solve by forcing use of statically linked llvm/clang libraries when
on OSX and using LLVM+clang 10+, even if the user did not explicitly
request that.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/cmake/modules/FindLLVM.cmake

@@ -91,6 +91,25 @@ foreach (COMPONENT clangFrontend clangDriver clangSerialization
 endforeach ()
 
 
+############ HACK ##############
+# On OSX, the Homebrew (and maybe any build) of LLVM 10.0 seems to have a
+# link conflict with its dependency on the llvm libc++ and the system
+# libc++, both can end up dynamically linked and lead to very subtle and
+# frustrating behavior failures (in particular, osl's use of libclang will
+# botch include file parsing any time LD_LIBRARY_PATH doesn't have the llvm
+# libc++ first).
+#
+# It seems that this is not a problem when linking against the llvm and
+# libclang libraries statically. So on apple and when LLVM 10+ are involved,
+# just force that choice. Other than larger execubales, it seems harmless,
+# and in any case a better choice than this beastly bug.
+#
+# We can periodically revisit this with new version of LLVM, maybe they will
+# fix things and we won't require this preemptive static linking.
+if (APPLE AND LLVM_VERSION VERSION_GREATER_EQUAL 10.0)
+    set (LLVM_STATIC ON)
+endif ()
+
 # shared llvm library may not be available, this is not an error if we use LLVM_STATIC.
 if ((LLVM_LIBRARY OR LLVM_LIBRARIES OR LLVM_STATIC) AND LLVM_INCLUDES AND LLVM_DIRECTORY AND LLVM_LIB_DIR)
   if (LLVM_STATIC)
@@ -100,8 +119,10 @@ if ((LLVM_LIBRARY OR LLVM_LIBRARIES OR LLVM_STATIC) AND LLVM_INCLUDES AND LLVM_D
     execute_process (COMMAND ${LLVM_CONFIG} --libfiles --link-static
                      OUTPUT_VARIABLE LLVM_LIBRARIES
                      OUTPUT_STRIP_TRAILING_WHITESPACE)
-    string (REPLACE " " ";" LLVM_LIBRARIES "${LLVM_LIBRARIES}")
-    set (LLVM_LIBRARY "")
+    if (LLVM_LIBRARIES)
+        string (REPLACE " " ";" LLVM_LIBRARIES "${LLVM_LIBRARIES}")
+        set (LLVM_LIBRARY "")
+    endif ()
   else ()
     set (LLVM_LIBRARIES "${LLVM_LIBRARY}")
   endif ()

src/liboslcomp/oslcomp.cpp

@@ -203,6 +203,7 @@ OSLCompilerImpl::preprocess_buffer (const std::string &buffer,
     headerOpts.UseBuiltinIncludes = 0;
     headerOpts.UseStandardSystemIncludes = 0;
     headerOpts.UseStandardCXXIncludes = 0;
+    // headerOpts.Verbose = 1;
     std::string directory = OIIO::Filesystem::parent_path(filename);
     if (directory.empty())
         directory = OIIO::Filesystem::current_path();