Re: CMake + clang failure

[Kornel Benko]

Am Samstag, 11. Juni 2016 um 08:25:58, schrieb Georg Baum 
<georg.b...@post.rwth-aachen.de>
> Guillaume Munch wrote:
>
> > Le 11/06/2016 03:00, Scott Kostyshak a écrit :
> >> -- Using GCC version 4.2.1
> >> CMake Error at CMakeLists.txt:267 (message):
> >>    gcc >= 4.3 is required.
> >
> >  From INSTALL:
> >
> >    First of all, you will need a recent C++ compiler, where recent means
> >    that the compilers are close to C++11 standard conforming like gcc (at
> >    least 4.3) or clang.
> >
> > I do not know clang, but I am surprised, gcc 4.2 is very old. I
> > requested to drop gcc 4.6 in a recent message.
>
> From config/lyxinclude.m4:
>
> dnl clang++ pretends to be g++ 4.2.1; this is not useful
>
> This is the reason why the version test now fails.
>
> I forgot to test cmake+clang when requiring a C++11 compiler.
> clang+autotools work fine. This is beyond my cmake knowledge. Kornel, do you
> have an idea how to fix this? autotools detect clang and then ignore the gcc
> version, see LYX_PROG_CLANG and the line I quoted (both from
> config/lyxinclude.m4).
>
>
> Georg

Should we really ignore output of '${CMAKE_CXX_COMPILER} -dumpversion'?

Some questions:
1.) What if the compiler is even older?
or
2.) Should we in this case assume GCC_VERSION >= 4.9?

One possible fix is appended.

        Kornel

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diff --git a/CMakeLists.txt b/CMakeLists.txt
index fee89e1..95a89d1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -261,16 +261,23 @@ endif()
 set(LYX_GCC11_MODE)
 if(UNIX OR MINGW)
 	execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE)
-	message(STATUS "Using GCC version ${GCC_VERSION}")
-	if(GCC_VERSION VERSION_LESS 4.9)
-		if(GCC_VERSION VERSION_LESS 4.3)
-			message(FATAL_ERROR "gcc >= 4.3 is required.")
-		endif()
-		# <regex> in gcc is unusable in versions less than 4.9.0
-		# see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53631
-		set(LYX_USE_STD_REGEX 0)
+	if (CMAKE_CXX_COMPILER_ID MATCHES "^[cC]lang$")
+	  # ignore the GCC_VERSION for clang
+	  # We pretend the compiler version >= 4.9
+	  message(STATUS "Using clang version ${GCC_VERSION}")
+	  set(LYX_USE_STD_REGEX 1)
 	else()
-		set(LYX_USE_STD_REGEX 1)
+	  message(STATUS "Using GCC version ${GCC_VERSION}")
+	  if(GCC_VERSION VERSION_LESS 4.9)
+		  if(GCC_VERSION VERSION_LESS 4.3)
+			  message(FATAL_ERROR "gcc >= 4.3 is required.")
+		  endif()
+		  # <regex> in gcc is unusable in versions less than 4.9.0
+		  # see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53631
+		  set(LYX_USE_STD_REGEX 0)
+	  else()
+		  set(LYX_USE_STD_REGEX 1)
+	  endif()
 	endif()
 	set(LYX_GCC11_MODE "${CXX11_FLAG}")
 else()