Apple - How to install recent clang++ with Homebrew?

As of 2018, the Homebrew Versions repository ('tap') is out of service.

The stock Homebrew llvm package still doesn't include clang/clang++, by default. Thus, it isn't part of the prebuilt ('bottled') package.

One can build it via:

brew install --with-toolchain llvm

And then use it via e.g.:

$ PATH="/usr/local/opt/llvm/bin:$PATH" \
    LDFLAGS='-L/usr/local/opt/llvm/lib -Wl,-rpath,/usr/local/opt/llvm/lib' \
    cmake ...

But this --with-toolchain induced build takes a very long time and is thus unsuitable in a continuous integration (CI) environment.

However, the clang that comes with recent XCode (which is available in CI environments like Travis-CI, Version 9 is the default, 10 available, too) isn't that outdated anymore as it used to be (Apple uses an fantasy version scheme for clang that doesn't match upstream clang version numbers but cmake detects e.g. for AppleClang 9.1.0.9020039 the version 4.0.1). Thus, it is sufficient to build C++11/C++14 software with common dependencies like Boost (e.g. version 1.67).

2016 State of the Art

The llvm package in Homebrew doesn't include clang++, by default. When installing it, you have to add --with-clang to the command line (e.g. brew install --with-clang llvm). The extra --with-clang yields a full package compile because there is only one prebuild ('bottled') llvm package available (without clang++). In addition to that: the llvm package is relatively old - currently it has llvm 3.6 - where 3.7 was released 6 months ago.

Thus, to get a bottled clang++ 3.7 you have to install the llvm package from Homebrew Versions:

$ brew tap homebrew/versions
$ brew install llvm37

It is then available under:

/usr/local/bin/clang++-3.7

The formula also notes:

To link to libc++, something like the following is required:
  CXX="clang++-3.7 -stdlib=libc++"
  CXXFLAGS="$CXXFLAGS -nostdinc++ -I/usr/local/opt/llvm37/lib/llvm-3.7/include/c++/v1"
  LDFLAGS="$LDFLAGS -L/usr/local/opt/llvm37/lib/llvm-3.7/lib"

Now it's enough to run:

brew install llvm

The bottle now includes clang by default.

You have to install it with --with-clang option:

$ brew install --with-clang llvm
==> Installing dependencies for llvm: cmake
==> Installing llvm dependency: cmake
==> Downloading https://homebrew.bintray.com/bottles/cmake-3.4.3.el_capitan.bottle.tar.gz
######################################################################## 100.0%
==> Pouring cmake-3.4.3.el_capitan.bottle.tar.gz
==> Caveats
Emacs Lisp files have been installed to:
  /usr/local/share/emacs/site-lisp/cmake
==> Summary
  /usr/local/Cellar/cmake/3.4.3: 1,980 files, 27.4M
==> Installing llvm
==> Downloading http://llvm.org/releases/3.6.2/llvm-3.6.2.src.tar.xz
######################################################################## 100.0%
==> Downloading http://llvm.org/releases/3.6.2/cfe-3.6.2.src.tar.xz
######################################################################## 100.0%
==> cmake -G Unix Makefiles /private/tmp/llvm20160211-42310-16fdrbw/llvm-3.6.2.src -DCMAKE_C_FLAGS_RELEASE=-DNDEBUG -DCMAKE_CXX_FLAGS_RELEAS
==> make
==> make install
==> Caveats
LLVM executables are installed in /usr/local/opt/llvm/bin.
Extra tools are installed in /usr/local/opt/llvm/share/llvm.

This formula is keg-only, which means it was not symlinked into /usr/local.

OS X already provides this software and installing another version in
parallel can cause all kinds of trouble.

Generally there are no consequences of this for you. If you build your
own software and it requires this formula, you'll need to add to your
build variables:

    LDFLAGS:  -L/usr/local/opt/llvm/lib
    CPPFLAGS: -I/usr/local/opt/llvm/include


If you need Python to find bindings for this keg-only formula, run:
  echo /usr/local/opt/llvm/lib/python2.7/site-packages >> /usr/local/lib/python2.7/site-packages/llvm.pth
==> Summary
  /usr/local/Cellar/llvm/3.6.2: 1,350 files, 338.2M, built in 21 minutes 18 seconds

Then, you will find clang++ on /usr/local/opt/llvm/bin/clang++.