[cmake-developers] [PATCH] FindRuby: Fix output check in _RUBY_CONFIG_VAR

[Evangelos Foutras]

Since commit 854e762 (FindRuby: clean up querying variables from Ruby)
we query RbConfig::CONFIG first and, if the command fails or its output
equates to a false constant, then fall back to querying Config::CONFIG.

Due to the above, an error condition exists with Ruby 2.2.0; when querying
RbConfig::CONFIG['TEENY'], the output of '0' will be discarded since it
matches the false constant '0'.

In previous versions this wasn't a problem, but Ruby 2.2 has completely
removed Config::CONFIG. This causes RUBY_VERSION_PATCH to be set to an
empty string and the Ruby version to be detected as '2.2.' (instead of
'2.2.0').

This patch fixes the output check to explicitly look for an empty string
before using the fallback query method. (Someone more familiar with Ruby
might be able to deem the fallback as unnecessary and fully remove it.)
---
 Modules/FindRuby.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/FindRuby.cmake b/Modules/FindRuby.cmake
index b5ac703..0950d15 100644
--- a/Modules/FindRuby.cmake
+++ b/Modules/FindRuby.cmake
@@ -90,7 +90,7 @@ if(RUBY_EXECUTABLE  AND NOT  RUBY_VERSION_MAJOR)
       RESULT_VARIABLE _RUBY_SUCCESS
       OUTPUT_VARIABLE _RUBY_OUTPUT
       ERROR_QUIET)
-    if(_RUBY_SUCCESS OR NOT _RUBY_OUTPUT)
+    if(_RUBY_SUCCESS OR _RUBY_OUTPUT STREQUAL "")
       execute_process(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['${RBVAR}']"
         RESULT_VARIABLE _RUBY_SUCCESS
         OUTPUT_VARIABLE _RUBY_OUTPUT
-- 
2.2.1