[banshee] configure: better guess for the C# compiler available

[AndrÃs Aragoneses <aaragoneses src gnome org>]

commit 3d3f7899465ee46e634b53c236401f612dac1492
Author: Andres G. Aragoneses <knocte gmail com>
Date:   Tue Dec 11 00:28:51 2012 +0000

    configure: better guess for the C# compiler available
    
    There are some distributions that bundle only a limited set of class
    libraries to be able to meet size requirements better. Such is the case
    of Ubuntu, which normally ships with only the subset compiled for the
    4.0 version of the runtime.
    
    In this case, the user may install the default Mono SDK packages when
    asked by the configure script, which only includes the 4.0 compiler by
    default (dmcs). At that point, banshee can already be compiled, but
    the configure script would insist in requiring a 2.0 compiler. If the
    user installs it, compiles Banshee and launches the "run" target, she
    may get a runtime exception because of a runtime version mismatch, like
    in bgo#675113.
    
    This problem is commonly known, and there is a clear workaround for it:
    http://orangesquash.org.uk/~laney/blog/posts/2011/10/mono-gotcha/
    However it poses a small barrier of entry for new developers that try
    to compile and run banshee from sources for the first time.
    
    Now the configure script is smarter and tries to guess harder if there
    is a C# compiler, even one that targets a higher version of the runtime
    than the one that is required to compile banshee.
    
    This possibility is only enabled in case the Mono version found is 2.8
    or higher, because Mono 2.6.1 included the 4.0 profile only as a
    "preview" [1] and might not be stable enough.
    
    [1] http://www.mono-project.com/Release_Notes_Mono_2.6.4#C.23_Language

 build/m4/shamrock/mono.m4 |   14 ++++++++++++++
 configure.ac              |    2 +-
 2 files changed, 15 insertions(+), 1 deletions(-)
---
diff --git a/build/m4/shamrock/mono.m4 b/build/m4/shamrock/mono.m4
index c40ecbf..309e163 100644
--- a/build/m4/shamrock/mono.m4
+++ b/build/m4/shamrock/mono.m4
@@ -8,6 +8,20 @@ AC_DEFUN([SHAMROCK_FIND_MONO_2_0_COMPILER],
 	SHAMROCK_FIND_PROGRAM_OR_BAIL(MCS, gmcs)
 ])
 
+AC_DEFUN([SHAMROCK_FIND_MONO_2_0_COMPILER_OR_HIGHER],
+[
+	SHAMROCK_FIND_PROGRAM(MCS, gmcs)
+	if test "x$MCS" = "x" ; then
+		if pkg-config --atleast-version=2.8 mono; then
+			SHAMROCK_FIND_PROGRAM(MCS, dmcs)
+		fi
+	fi
+
+	if test "x$MCS" = "x" ; then
+		AC_MSG_ERROR([You need to install 'gmcs'])
+	fi
+])
+
 AC_DEFUN([SHAMROCK_FIND_MONO_4_0_COMPILER],
 [
 	SHAMROCK_FIND_PROGRAM_OR_BAIL(MCS, dmcs)
diff --git a/configure.ac b/configure.ac
index 50f2c4f..7ea5157 100644
--- a/configure.ac
+++ b/configure.ac
@@ -67,7 +67,7 @@ SHAMROCK_CHECK_GNOME_DOC_UTILS(0.17.3)
 
 dnl Mono and gmcs
 SHAMROCK_CHECK_MONO_MODULE(2.4.3)
-SHAMROCK_FIND_MONO_2_0_COMPILER
+SHAMROCK_FIND_MONO_2_0_COMPILER_OR_HIGHER
 SHAMROCK_FIND_MONO_RUNTIME
 SHAMROCK_CHECK_MONO_2_0_GAC_ASSEMBLIES([Mono.Cairo Mono.Posix ICSharpCode.SharpZipLib])