Also detect llvm-config from build tree

CMakeLists.txt

@@ -18,7 +18,7 @@ macro_log_feature(CLANG_FOUND "libclang" "LibClang is a high level C interface t
 
 add_definitions(${LLVM_CFLAGS})
 include_directories(
-    ${LLVM_INCLUDE_DIR}
+    ${CLANG_INCLUDE_DIR}
 )
 
 if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "Intel")

cmake/FindClang.cmake

 # Detect Clang libraries
 #
 # Defines the following variables:
+#  CLANG_FOUND                 - True if Clang was found
+#  CLANG_INCLUDE_DIR           - Where to find Clang includes
+#  CLANG_LIBRARY_DIR           - Where to find Clang libraries
+#
 #  CLANG_CLANG_LIB             - LibClang library
 #  CLANG_CLANGFRONTEND_LIB     - Clang Frontend Library
 #  CLANG_CLANGDRIVER_LIB       - Clang Driver Library
@@ -19,6 +23,7 @@
 # This software is distributed WITHOUT ANY WARRANTY; without even the
 # implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 # See the License for more information.
+
 #=============================================================================
 
 find_package(LLVM ${Clang_FIND_VERSION} ${Clang_FIND_REQUIRED})
@@ -28,7 +33,7 @@ set(CLANG_FOUND FALSE)
 if (LLVM_FOUND AND LLVM_LIBRARY_DIR)
   macro(FIND_AND_ADD_CLANG_LIB _libname_)
     string(TOUPPER ${_libname_} _prettylibname_)
-    find_library(CLANG_${_prettylibname_}_LIB ${_libname_} ${LLVM_LIBRARY_DIR} ${CLANG_LIB_DIR})
+    find_library(CLANG_${_prettylibname_}_LIB ${_libname_} ${LLVM_LIBRARY_DIR})
     if(CLANG_${_prettylibname_}_LIB)
       set(CLANG_LIBS ${CLANG_LIBS} ${CLANG_${_prettylibname_}_LIB})
     endif()
@@ -66,8 +71,24 @@ else()
 endif()
 
 if(CLANG_FOUND)
-  message(STATUS "Found Clang: ${LLVM_INCLUDE_DIR}")
-  message(STATUS "  Libraries: ${CLANG_LIBS}")
+  set(CLANG_LIBRARY_DIR ${LLVM_LIBRARY_DIR})
+  set(CLANG_INCLUDE_DIR ${LLVM_INCLUDE_DIR})
+
+  # check whether llvm-config comes from an install prefix
+  execute_process(
+    COMMAND ${LLVM_CONFIG_EXECUTABLE} --src-root
+    OUTPUT_VARIABLE _llvmSourceRoot
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+  )
+  string(FIND "${LLVM_INCLUDE_DIR}" "${_llvmSourceRoot}" _llvmIsInstalled)
+  if (NOT _llvmIsInstalled)
+    message(STATUS "Detected that llvm-config comes from a build-tree, adding includes from source dir")
+    list(APPEND CLANG_INCLUDE_DIR "${_llvmSourceRoot}/tools/clang/include")
+  endif()
+
+  message(STATUS "Found Clang (LLVM version: ${LLVM_VERSION}")
+  message(STATUS "  Include dirs:  ${CLANG_INCLUDE_DIR}")
+  message(STATUS "  Libraries:     ${CLANG_LIBS}")
 else()
   if(Clang_FIND_REQUIRED)
     message(FATAL_ERROR "Could NOT find Clang")