allow RelWithDebInfo, improve FindClangTools

SetupCxxFlags.cmake does not list "RELWITHDEBINFO" in the final flag
setup, so cmake will error out if that build config is selected. It's
handy for quick debugging without switching your python build etc over
to "DEBUG".

FindClangTools.cmake could check the version of 'clang-format' (no
version suffix) to see if it satisfies a version requirement.

add note about clang tools path

cpp/README.md

@@ -428,6 +428,12 @@ You may find the required packages at http://releases.llvm.org/download.html
 or use the Debian/Ubuntu APT repositories on https://apt.llvm.org/. On macOS
 with [Homebrew][1] you can get it via `brew install llvm@6`.
 
+Depending on how you installed clang-format, the build system may not be able
+to find it. You can provide an explicit path to your LLVM installation (or the
+root path for the clang tools) with the environment variable
+`$CLANG_TOOLS_PATH` or by passing `-DClangTools_PATH=$PATH_TO_CLANG_TOOLS` when
+invoking CMake.
+
 ## Checking for ABI and API stability
 
 To build ABI compliance reports, you need to install the two tools

cpp/cmake_modules/FindClangTools.cmake

@@ -20,7 +20,7 @@
 # Variables used by this module, they can change the default behaviour and need
 # to be set before calling find_package:
 #
-#  ClangToolsBin_HOME -
+#  ClangTools_PATH -
 #   When set, this path is inspected instead of standard library binary locations
 #   to find clang-tidy and clang-format
 #
@@ -75,10 +75,11 @@ if (CLANG_FORMAT_VERSION)
     )
 
     # If not found yet, search alternative locations
-    if (("${CLANG_FORMAT_BIN}" STREQUAL "CLANG_FORMAT_BIN-NOTFOUND") AND APPLE)
+    if ("${CLANG_FORMAT_BIN}" STREQUAL "CLANG_FORMAT_BIN-NOTFOUND")
+      STRING(REGEX REPLACE "^([0-9]+)\\.[0-9]+" "\\1" CLANG_FORMAT_MAJOR_VERSION "${CLANG_FORMAT_VERSION}")
+      STRING(REGEX REPLACE "^[0-9]+\\.([0-9]+)" "\\1" CLANG_FORMAT_MINOR_VERSION "${CLANG_FORMAT_VERSION}")
+      if (APPLE)
         # Homebrew ships older LLVM versions in /usr/local/opt/llvm@version/
-        STRING(REGEX REPLACE "^([0-9]+)\\.[0-9]+" "\\1" CLANG_FORMAT_MAJOR_VERSION "${CLANG_FORMAT_VERSION}")
-        STRING(REGEX REPLACE "^[0-9]+\\.([0-9]+)" "\\1" CLANG_FORMAT_MINOR_VERSION "${CLANG_FORMAT_VERSION}")
         if ("${CLANG_FORMAT_MINOR_VERSION}" STREQUAL "0")
             find_program(CLANG_FORMAT_BIN
               NAMES clang-format
@@ -102,7 +103,27 @@ if (CLANG_FORMAT_VERSION)
                   NO_DEFAULT_PATH
           )
         endif()
+      else()
+        # try searching for "clang-format" and check the version
+        find_program(CLANG_FORMAT_BIN
+          NAMES clang-format
+          PATHS
+                ${ClangTools_PATH}
+                $ENV{CLANG_TOOLS_PATH}
+                /usr/local/bin /usr/bin
+                NO_DEFAULT_PATH
+        )
+        if (NOT ("${CLANG_FORMAT_BIN}" STREQUAL "CLANG_FORMAT_BIN-NOTFOUND"))
+          execute_process(COMMAND ${CLANG_FORMAT_BIN} "-version"
+            OUTPUT_VARIABLE CLANG_FORMAT_FOUND_VERSION_MESSAGE
+            OUTPUT_STRIP_TRAILING_WHITESPACE)
+          if (NOT ("${CLANG_FORMAT_FOUND_VERSION_MESSAGE}" MATCHES "^clang-format version ${CLANG_FORMAT_MAJOR_VERSION}\\.${CLANG_FORMAT_MINOR_VERSION}.*"))
+            set(CLANG_FORMAT_BIN "CLANG_FORMAT_BIN-NOTFOUND")
+          endif()
+        endif()
+      endif()
     endif()
+
 else()
     find_program(CLANG_FORMAT_BIN
       NAMES clang-format-4.0

cpp/cmake_modules/SetupCxxFlags.cmake

@@ -365,6 +365,7 @@ message("Configured for ${CMAKE_BUILD_TYPE} build (set with cmake -DCMAKE_BUILD_
 if ("${CMAKE_BUILD_TYPE}" STREQUAL "DEBUG")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${C_FLAGS_DEBUG}")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CXX_FLAGS_DEBUG}")
+elseif ("${CMAKE_BUILD_TYPE}" STREQUAL "RELWITHDEBINFO")
 elseif ("${CMAKE_BUILD_TYPE}" STREQUAL "FASTDEBUG")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${C_FLAGS_FASTDEBUG}")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CXX_FLAGS_FASTDEBUG}")