gnuplot: fix AquaTerm 1.1.1 library detection

Gnuplot supports use of AquaTerm as an output device on OSX, provided
it detects an installed AquaTerm at build time. AquaTerm provides its
support through a framework named 'AquaTerm', which is installed in the
standard location '/Library/Frameworks'.

Gnuplot v4.6.3 does not detect the current version of AquaTerm, v1.1.1,
which was released in July 2012. This is due to a small change to the
standard AquaTerm installation, which is designed to encourage client
software to link to the framework using '-framework' style compiler
options, in place of the traditional library style options. Gnuplot's
trunk (v4.7) does now use this '-framework' style.

References:
https://github.com/AquaTerm/AquaTerm/blob/v1.1.1/aquaterm/ReleaseNotes#L1-11
https://github.com/AquaTerm/AquaTerm/blob/v1.1.1/aquaterm/INSTALL#L7-15

This formula change modifies Gnuplot 4.6.x's configure script to
generate '-framework' style options, thereby allowing a standard
installation of AquaTerm v1.1.1 to be detected. It also makes a minor
modification to an 'import' specification, which is probably only of
relevance on a case sensitive file system.

Gnuplot trunk now includes a '--with-aquaterm' configure option, which
is required before it will attempt to detect AquaTerm. This change adds
a 'noaquaterm' option to the formula to support this (so we default to
--with-aquaterm). The option will also be effective with Gnuplot v4.6.x.

Closes Homebrew/homebrew#25121.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/gnuplot.rb

@@ -30,6 +30,7 @@ class Gnuplot < Formula
   option 'tests',  'Verify the build with make check (1 min)'
   option 'without-emacs', 'Do not build Emacs lisp files'
   option 'latex',  'Build with LaTeX support'
+  option 'without-aquaterm', 'Do not build AquaTerm support'
 
   depends_on 'pkg-config' => :build
   depends_on LuaRequirement unless build.include? 'nolua'
@@ -43,6 +44,26 @@ class Gnuplot < Formula
   depends_on :tex          if build.include? 'latex'
 
   def install
+    if build.with? "aquaterm"
+      # Add "/Library/Frameworks" to the default framework search path, so that an
+      # installed AquaTerm framework can be found. Brew does not add this path
+      # when building against an SDK (Nov 2013).
+      ENV.prepend "CPPFLAGS", "-F/Library/Frameworks"
+      ENV.prepend "LDFLAGS", "-F/Library/Frameworks"
+
+      unless build.head?
+        # Fix up Gnuplot v4.6.x to accommodate framework style linking. This is
+        # required with a standard install of AquaTerm 1.1.1 and is supported under
+        # earlier versions of AquaTerm. Refer:
+        # https://github.com/AquaTerm/AquaTerm/blob/v1.1.1/aquaterm/ReleaseNotes#L1-11
+        # https://github.com/AquaTerm/AquaTerm/blob/v1.1.1/aquaterm/INSTALL#L7-15
+        inreplace "configure", "-laquaterm", "-framework AquaTerm"
+        inreplace "term/aquaterm.trm", "<aquaterm/AQTAdapter.h>", "<AquaTerm/AQTAdapter.h>"
+      end
+    elsif !build.head?
+      inreplace "configure", "-laquaterm", ""
+    end
+
     # Help configure find libraries
     readline = Formula.factory 'readline'
     pdflib = Formula.factory 'pdflib-lite'
@@ -61,6 +82,7 @@ class Gnuplot < Formula
     args << '--enable-qt'             if build.include? 'qt'
     args << '--without-lua'           if build.include? 'nolua'
     args << '--without-lisp-files'    if build.include? 'without-emacs'
+    args << build.with?('aquaterm') ? '--with-aquaterm' : '--without-aquaterm'
 
     if build.include? 'latex'
       args << '--with-latex'
@@ -81,4 +103,15 @@ class Gnuplot < Formula
   def test
     system "#{bin}/gnuplot", "--version"
   end
+
+  def caveats
+    if build.with? "aquaterm"
+      <<-EOS.undent
+        AquaTerm support will only be built into Gnuplot if the standard AquaTerm
+        package from SourceForge has already been installed onto your system.
+        If you subsequently remove AquaTerm, you will need to uninstall and then
+        reinstall Gnuplot.
+      EOS
+    end
+  end
 end