global: Rebuild PHP parser for GNU GLOBAL.

GNU GLOBAL is distributed with a PHP parser generated with an older
version of flex(1). That parser has some limitation (see
http://comments.gmane.org/gmane.comp.gnu.global.bugs/1439).

Added a rebuild of the PHP parser to the install target.

Closes Homebrew#13814.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Formula/global.rb

@@ -6,13 +6,42 @@ class Global < Formula
   mirror 'http://ftp.gnu.org/gnu/global/global-6.2.4.tar.gz'
   sha1 'fff915079e7099de0174c47a1a8f6a5b870517d5'
 
+  option "without-rebuilding-php-parser", "Don't rebuild PHP parser; use provied parser"
+
   def install
-    system "./configure", "--prefix=#{prefix}", "--disable-dependency-tracking"
+    # Rebuilding the PHP parser, see:
+    # http://comments.gmane.org/gmane.comp.gnu.global.bugs/1439
+    unless build.include? "without-rebuilding-php-parser"
+      system "flex -o libparser/php.c libparser/php.l"
+    end
+
+    system "./configure", "--disable-dependency-tracking",
+                          "--prefix=#{prefix}"
     system "make install"
 
     # we copy these in already
-    cd share+'gtags' do
+    cd share/'gtags' do
       rm %w[README COPYING LICENSE INSTALL ChangeLog AUTHORS]
     end
   end
+
+  def caveats; <<-EOS.undent
+    GNU GLOBAL is distributed with a PHP parser generated with an
+    old version of flex(1). That parser has some limitation. See:
+      http://comments.gmane.org/gmane.comp.gnu.global.bugs/1439
+
+    Installing GNU GLOBAL with Homebrew will therefor rebuild the
+    PHP parser using Mac OS X' newer version of flex(1) which
+    generates a parser without the limit.
+
+    You can install GNU GLOBAL without rebuilding the PHP parser
+    (and instead use the parser distributed by GNU GLOBAL) by using
+    the option '--without-rebuilding-php-parser':
+
+      brew install global --without-rebuilding-php-parser
+
+    Use i.e. if you want to be sure whether a problem is caused by
+    the rebuild parser or some other thing in GNU GLOBAL.
+    EOS
+  end
 end