tests: don't use C instead of C++ compiler on case-insensitive platforms

This change fixes automake bug#11893 and bug#10766.

On at least Cygwin and Mac OS X 10.7, the file system where the system
compilers are located can be case-insensitive, so that looking for a
program named 'CC' might actually find the C compiler in /usr/bin/cc.

Now, the Automake configure script looks for a C++ compiler named 'CC'
before looking for more obvious names like c++ or g++ (that is done to
increase testsuite "coverage in the wild", e.g., preferring, on Solaris,
the Sun Studio C++ compiler /usr/bin/CC over the GNU C++ compiler).

Since the checks done in AC_PROG_CXX are apparently not strict enough
to rule out C compilers like those from GCC or Clang (which are smart
enough to recognize if a file has a C++ extension, passing it to the
C++ front end) the testsuite might end up using a C compiler where a
C++ one is expected, with some subtle bad consequences.

* configure.ac: Don't look for a C++ compiler named 'CC' if the
"top-level" file system(s) (where /bin and /usr/bin are) are detected
to be case-insensitive.

Reported-by: Peter Rosin <peda@lysator.liu.se>
Reported-by: Max Horn <max@quendi.de>
Helped-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

diff --git a/configure.ac b/configure.ac
index 49b008d..d49da6c 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -442,12 +442,23 @@ _AM_COMPILER_CAN_FAIL(dnl
 
 AS_IF([test x"$GCC" = x"yes"], [am_CC_is_GNU=yes], [am_CC_is_GNU=no])
 
+# On case-insensitive file systems (seen e.g. on Cygwin and Mac OS X)
+# we must avoid looking for 'CC', because that would be the same as
+# 'cc', and could cause $CXX to point to the C compiler, instead of
+# to a C++ compiler as expected.  See automake bugs #11893 and #10766.
+if test -f /bIn/rMdIr || test -f /uSr/bIn/rMdIr; then
+  # Case-insensitive file system, don't look for CC.
+  am_CC=
+else
+  am_CC=CC
+fi
+
 # The list of C++ compilers here has been copied, pasted and edited
 # from 'lib/autoconf/c.m4:AC_PROG_CXX' in the Autoconf distribution.
 # Keep it in sync, or better again, find out a way to avoid this code
 # duplication.
 _AM_COMPILER_CAN_FAIL([AC_PROG_CXX(dnl
-  [aCC CC FCC KCC RCC xlC_r xlC c++ cxx cc++ gpp g++])],
+  [aCC $am_CC FCC KCC RCC xlC_r xlC c++ cxx cc++ gpp g++])],
   [CXX=false; _AM_SKIP_COMP_TESTS([C++])])
 
 AS_IF([test x"$GXX" = x"yes"], [am_CXX_is_GNU=yes], [am_CXX_is_GNU=no])