Cannot install gcc48 with homebrew - macos

Question

I cannot install gcc48 with homebrew. The install fails with
(starting from the last lines in configures output):
checking for version 0.10 of ISL... no
checking for version 0.11 of ISL... no
configure: error: Unable to find a usable ISL. See config.log for details.
==> Formula
Tap: homebrew/versions
Path: /usr/local/Library/Taps/homebrew-versions/gcc48.rb
==> Configuration
HOMEBREW_VERSION: 0.9.4
HEAD: e2b10438666f41366f596fe762b2455f5761bcd8
CPU: 8-core 64-bit sandybridge
OS X: 10.8.4-x86_64
Xcode: 4.6.3
CLT: 4.6.0.0.1.1365549073
X11: 2.7.4 => /opt/X11
==> ENV
HOMEBREW_CC: clang
MAKEFLAGS: -j1
CMAKE_PREFIX_PATH: /usr/local
CMAKE_INCLUDE_PATH: /opt/X11/include/freetype2:/usr/include/libxml2:/opt/X11/include
CMAKE_LIBRARY_PATH: /opt/X11/lib
PKG_CONFIG_PATH: /usr/local/opt/isl/lib/pkgconfig:/usr/local/opt/cloog/lib/pkgconfig
PKG_CONFIG_LIBDIR: /usr/lib/pkgconfig:/usr/local/Library/ENV/pkgconfig/10.8:/opt/X11/lib/pkgconfig:/opt/X11/share/pkgconfig
HOMEBREW_MAKE_JOBS: 1
ACLOCAL_PATH: /usr/local/share/aclocal:/opt/X11/share/aclocal
OBJC: cc
PATH: /usr/local/Library/ENV/4.3:/usr/local/opt/cloog/bin:/opt/X11/bin:/usr/bin:/bin:/usr/sbin:/sbin
Error: gcc48 did not build
I do have isl installed.
: brew info isl
isl: stable 0.12, HEAD
http://www.kotnet.org/~skimo/isl/
/usr/local/Cellar/isl/0.12 (55 files, 3.2M) *
Built from source
From: https://github.com/mxcl/homebrew/commits/master/Library/Formula/isl.rb
==> Dependencies
Required: gmp

Answer 1

GCC has imposed a strict requirement about ISL version. At the time being both 4.8 branch and trunk (4.9) requires ISL 0.10 or 0.11. Homebrew has temporarily reverted ISL to 0.11.2 so it should be fine now.

Answer 2

This isn't restricted to Homebrew. There's a problem with the configure script if cloog-0.18.0 uses the bundled sub-package of isl-0.11.1. The VERSION string is not correctly substituted, and is set to "UNKNOWN" in the isl_version() function call - the value that the gcc configure script is testing.
You might have to build (or install) ISL first, and then add --with-isl-prefix=$SOME_DIR to the cloog configure options, so it uses the external ISL installation. I built gcc-4.8.1 for AVR recently from source, and used:
## isl-0.11.1 # ftp://gcc.gnu.org/pub/gcc/infrastructure/
> ../configure --prefix=$CROSSDIR --with-gmp-prefix=$CROSSDIR
> make [check]; make install; rehash
and now build cloog-0.18.0 with the installed 'system' ISL:
> ../configure --prefix=$CROSSDIR --with-isl-prefix=$CROSSDIR \
--with-gmp-prefix=$CROSSDIR
> make [check]; make install; rehash
This also required adding: --with-isl=$CROSSDIR to the gcc configure options.