Bug report:

Default Troubleshooting

• Ran brew update and retried your prior step?
• Ran brew doctor, fixed as many issues as possible and retried your prior step?
• Confirmed this is a problem with specific formulae and not Homebrew/brew? If it's a general Homebrew/brew problem please file this issue at https://github.com/Homebrew/brew/issues/new

Expected Behavior

I expected brew install mu --with-emacs to install without error.

Actual Behavior

brew install mu --with-emacs fails on macOS Sierra 10.12.3. In contrast, brew install mu works just fine.

Attempted Diagnosis

The build logs may be difficult to follow, so here's what I did.

Initially, the install failed with this error:

Package guile-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `guile-2.0.pc'
to the PKG_CONFIG_PATH environment variable

Installing guile did not fix the problem, so I edited the formula to disable guile. I also disabled gtk & webkit for good measure. In short, I changed this:

    system "./configure", "--disable-dependency-tracking",
                          "--prefix=#{prefix}",
                          "--with-lispdir=#{elisp}"

to this:

    system "./configure", "--disable-dependency-tracking",
                          "--prefix=#{prefix}",
                          "--with-lispdir=#{elisp}",
                          "--disable-gtk",
                          "--disable-guile",
                          "--disable-webkit"

I've put my (failed) additions on my own branch.

The build log is here.

I tried this both with the standard emacs formula and emacs-plus, but got the same result from both. I also set $EMACS to /usr/local/bin/emacs without success.

Related Issues

I failed to compile mu manually and filed an issue with mu itself.

gist-logs

Here are the gist-logs.

My brew config output

HOMEBREW_VERSION: 1.1.11-132-g17cc40f1
ORIGIN: https://github.com/Homebrew/brew
HEAD: 17cc40f112cbb7e5da5ef6d8eb3e3d5afbbd43e5
Last commit: 18 hours ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 51d046569a1fc72d835449e705f60a7528081280
Core tap last commit: 3 hours ago
HOMEBREW_PREFIX: /usr/local
HOMEBREW_REPOSITORY: /usr/local/Homebrew
HOMEBREW_CELLAR: /usr/local/Cellar
HOMEBREW_BOTTLE_DOMAIN: https://homebrew.bintray.com
CPU: quad-core 64-bit haswell
Homebrew Ruby: 2.0.0-p648
Clang: 8.0 build 800
Git: 2.12.1 => /usr/local/bin/git
Perl: /usr/local/bin/perl => /usr/local/Cellar/perl/5.24.1/bin/perl
Python: /usr/local/bin/python => /usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/bin/python2.7
Ruby: /usr/local/bin/ruby => /usr/local/Cellar/ruby/2.4.0/bin/ruby
Java: 1.8.0_102, 1.8.0_66
macOS: 10.12.3-x86_64
Xcode: 8.2.1
CLT: 8.2.0.0.1.1480973914
X11: 2.7.9 => /opt/X11

My brew doctor output

Your system is ready to brew.

Solution without Mono

Here is recipe to build it without Mono - https://gist.github.com/KryDos/d306d6453ad0f30b55468aecc8eb09a3
Nothing is changed except def install => resource("gmime") section

Description

I didn't try solution by @neurolit since Mono is pretty big dependency as for me. But thanks anyway!

I never dived into how Homebrew works but here I noticed brew edit command which is really great :)

So, I researched a bit and found that gmime package (required by mu) can be compiled with --disable-mono option (and actually it was compiled with this option before 3.0.0 version). At this stage it compiles but mu isn't working because something wrong with linker.
But if I manually set GMIME_LIBS and GMIME_CFLAGS then it works.

Would you accept pull request for this? But I'm actually not sure what I fixed and I don't even know what is pkgconfig which is probably something related

I think I made the changes correctly. Thank you for the detailed

brew edit mu

command, I hadn't used that one before.

def install
 resource("gmime").stage do
   system "./configure", "--prefix=#{prefix}/gmime", "--disable-introspection"
   system "make", "install"
   ENV.append_path "PKG_CONFIG_PATH", "#{prefix}/gmime/lib/pkgconfig"
   ENV.append_path "C_INCLUDE_PATH", "#{prefix}/gmime/include/gmime-2.6"
   ENV.append_path "CMAKE_INCLUDE_PATH", "#{prefix}/gmime/include/gmime-2.6"
   ENV.append_path "CMAKE_LIBRARY_PATH", "#{prefix}/gmime/lib"
 end
system "autoreconf", "-ivf"
system "./configure", "--disable-dependency-tracking",
                      "--prefix=#{prefix}",
                      "--with-lispdir=#{elisp}",
                      "--disable-guile",
                      "--disable-gtk",
                      "--disable-webkit"
system "make"

Still getting an error.

checking for mcs... /usr/local/bin/mcs
checking whether /usr/local/bin/mcs is GNU Mono... yes 
checking for gacutil... /usr/local/bin/gacutil
checking for GLIB_SHARP... no

configure: error: Package requirements (glib-sharp-2.0 >= 2.4.0) were not met: