find ruby gems & make coverage conditional on BUILD_COVERAGE

Summary:
new finding tech:
- find_gem function configures gem-specific FindFoo files and wraps around
  find_package
- FindFoo files look for ruby and then attempt to require the gem name
  i.e. it checks if the gem can be successfully loaded by the interpreter
- since this is based on find_package it may be influenced in all the
  regular ways (e.g. forced found or disabled from finding altogether
  via CMAKE_DISABLE_FIND_PACKAGE_$PKGNAME)

various notes for the future:
- technically this isn't 100% correct because the require name of a gem and
  the gem name may not be the same. e.g. the gem `docker-api` has the
  require name `docker`. for all currently used gems the names are however
  the same and so simply requiring the gem name is expected to work
- the implementation doesn't care about versions, again because we don't
  need it to
- test-unit is a bundled gem, some distributions (e.g. Arch) do split it
  out without making suitable dependency arrangements on a package level
  though

the tech is heavily inspired by Aleix Pol's tech for finding QML modules
as seen in extra-cmake-modules

Test Plan:
- ruby not found: none of the modules found
- test-unit not present: error
- simplecov not prseent: never errors
- having a module installed or not is reported in the cmake output

Reviewers: #dolphin, elvisangelaccio

Reviewed By: #dolphin, elvisangelaccio

Subscribers: elvisangelaccio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D19856

1 files changed, 53 insertions, 0 deletions

diff --git a/cmake/FindGem.cmake.in b/cmake/FindGem.cmake.in
new file mode 100644
index 000000000..0dcc67766
--- /dev/null
+++ b/cmake/FindGem.cmake.in
@@ -0,0 +1,53 @@
+#=============================================================================
+# Copyright (c) 2019 Harald Sitter <[email protected]>
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+# 3. The name of the author may not be used to endorse or promote products
+#    derived from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#=============================================================================
+
+find_program(RUBY_EXE ruby)
+if(NOT RUBY_EXE)
+    message(WARNING "Could not find ruby program")
+    return()
+endif()
+
+execute_process(
+    COMMAND ${RUBY_EXE} -e "require '@GEM_NAME@'"
+    ERROR_VARIABLE ERROR_VAR
+    RESULT_VARIABLE RESULT_VAR
+)
+
+if(RESULT_VAR EQUAL 0)
+    set(@GEM_PACKAGE@_FOUND TRUE)
+else()
+    message(WARNING ${ERROR_VAR})
+    return()
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(@GEM_PACKAGE@
+    FOUND_VAR
+        @GEM_PACKAGE@_FOUND
+    REQUIRED_VARS
+        @GEM_PACKAGE@_FOUND
+)