mpich2: Add option to re-enable shared libs

MPICH2 fails to build with clang because of a clang (and/or ld) bug with
Xcode 4.5.1.  Issue originally reported to homebrew in #15533, "fixed"
by disabling shared libraries altogether in bcb64c7.

- Add an `--enable-shared` option
- Add a `fails_with :clang` when building shared libs
- Upstream is aware of the issue, but has no workaround besides using
  `llvm-gcc` when building shared libs
- MacPorts is using a similar workaround at this time.
- Tested on 10.7.5 with Xcode 4.5.2 with and without `--enable-shared`

Closes #16299.

Signed-off-by: Charlie Sharpsteen <source@sharpsteen.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/Library/Formula/mpich2.rb b/Library/Formula/mpich2.rb
index 130f2166a..00a69d72e 100644
--- a/Library/Formula/mpich2.rb
+++ b/Library/Formula/mpich2.rb
@@ -15,6 +15,18 @@ class Mpich2 < Formula
   end
 
   option 'disable-fortran', "Do not attempt to build Fortran bindings"
+  option 'enable-shared', "Build shared libraries"
+
+  # fails with clang from Xcode 4.5.1 on 10.7 and 10.8 (see #15533)
+  fails_with :clang do
+    build 421
+    cause <<-EOS.undent
+      Clang generates code that causes the linker to segfault when building
+      MPICH2 with shared libraries.  Specific message:
+
+          collect2: ld terminated with signal 11 [Segmentation fault: 11]
+      EOS
+  end if build.include? 'enable-shared'
 
   def install
     if build.head?
@@ -36,6 +48,11 @@ class Mpich2 < Formula
       ENV.fortran
     end
 
+    # MPICH2 configure defaults to "--disable-shared"
+    if build.include? 'enable-shared'
+      args << "--enable-shared"
+    end
+
     system "./configure", *args
     system "make"
     system "make install"