`find_package(Ruby)` returns incorrect paths on macOS

• CMake Version: 3.7.0 (installed by brew install cmake)
• OS: macOS Sierra 10.12.1

Detailed steps to reproduce the problem

• Install Ruby 2.3 by brew install ruby.
• Create CMakeLists.txt with below content.

cmake_minimum_required (VERSION 3.7.0)
project(bug)
set(_RUBY_DEBUG_OUTPUT ON)
find_package(Ruby 2.3 REQUIRED)

• Run cmake .

What happened

CMake finds Ruby header and libraries, which are all pointed to the system framework (as shown in below log). However, this is incorrect. Because the version of system Ruby is 2.0 instead of 2.3 as required by CMakeLists.txt.

[snip]
-- --------FindRuby.cmake debug------------
-- _RUBY_POSSIBLE_EXECUTABLE_NAMES: ruby2.3;ruby23;ruby;ruby2.1;ruby21;ruby2.0;ruby20;ruby1.9;ruby19;ruby1.8;ruby18
-- _RUBY_POSSIBLE_LIB_NAMES: ruby;ruby-static;ruby2.3;ruby23;ruby-2.3;ruby-2.3.0
-- RUBY_ARCH_DIR: /usr/local/Cellar/ruby/2.3.1_2/lib/ruby/2.3.0/x86_64-darwin16
-- RUBY_HDR_DIR: /usr/local/Cellar/ruby/2.3.1_2/include/ruby-2.3.0
-- RUBY_POSSIBLE_LIB_DIR: /usr/local/Cellar/ruby/2.3.1_2/lib
-- Found RUBY_VERSION: "2.3.0" , short: "2.3", nodot: "23"
-- _RUBY_REQUIRED_VARS: RUBY_EXECUTABLE;RUBY_INCLUDE_DIR;RUBY_LIBRARY;RUBY_CONFIG_INCLUDE_DIR
-- RUBY_EXECUTABLE: /usr/local/bin/ruby
-- RUBY_LIBRARY: /System/Library/Frameworks/ruby.framework
-- RUBY_INCLUDE_DIR: /System/Library/Frameworks/Ruby.framework/Headers
-- RUBY_CONFIG_INCLUDE_DIR: /System/Library/Frameworks/Ruby.framework/Headers
-- --------------------
-- Found Ruby: /usr/local/bin/ruby (found suitable version "2.3.0", minimum required is "2.3")
[snip]

What should have happened

It should set RUBY_LIBRARY, RUBY_INCLUDE_DIR and RUBY_CONFIG_INCLUDE_DIR to Homebrew Ruby(v2.3) instead of system Ruby(v2.0).

Cause and Workaround

This is caused as by default CMake has CMAKE_FIND_FRAMEWORK as First on macOS. In turn, find_library and find_path inside FindRuby.cmake will search macOS Framework before the paths supplied by HINTS.

Related Codes which trigger the bug:

• find_path in FindRuby.cmake: https://github.com/Kitware/CMake/blob/v3.7.0/Modules/FindRuby.cmake#L182-L187
• find_library in FindRuby.cmake: https://github.com/Kitware/CMake/blob/v3.7.0/Modules/FindRuby.cmake#L238
• Framework path by default has higher priority over HINTS: https://github.com/Kitware/CMake/blob/v3.7.0/Source/cmFindPathCommand.cxx#L48-L61

I suspect this bug has wider impact than just Ruby. It may be triggered by other macOS system Framework libraries (e.g. Python). To solve it, I think HINTS should have the highest priority, regardless the value of CMAKE_FIND_FRAMEWORK.

To workaround it, set CMAKE_FIND_FRAMEWORK to Last in CMakeLists.txt.