Check that the SCM log file is writable before using it (#13541).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11698 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/scm/adapters/abstract_adapter.rb

@@ -219,18 +219,39 @@ module Redmine
         end
 
         # Path to the file where scm stderr output is logged
+        # Returns nil if the log file is not writable
         def self.stderr_log_file
-          @stderr_log_path ||=
-            Redmine::Configuration['scm_stderr_log_file'].presence ||
-            Rails.root.join("log/#{Rails.env}.scm.stderr.log").to_s
+          if @stderr_log_file.nil?
+            writable = false
+            path = Redmine::Configuration['scm_stderr_log_file'].presence
+            path ||= Rails.root.join("log/#{Rails.env}.scm.stderr.log").to_s
+            if File.exists?(path)
+              if File.file?(path) && File.writable?(path) 
+                writable = true
+              else
+                logger.warn("SCM log file (#{path}) is not writable")
+              end
+            else
+              begin
+                File.open(path, "w") {}
+                writable = true
+              rescue => e
+                logger.warn("SCM log file (#{path}) cannot be created: #{e.message}")
+              end
+            end
+            @stderr_log_file = writable ? path : false
+          end
+          @stderr_log_file || nil
         end
 
         def self.shellout(cmd, options = {}, &block)
           if logger && logger.debug?
             logger.debug "Shelling out: #{strip_credential(cmd)}"
             # Capture stderr in a log file
+            if stderr_log_file
               cmd = "#{cmd} 2>>#{shell_quote(stderr_log_file)}"
             end
+          end
           begin
             mode = "r+"
             IO.popen(cmd, mode) do |io|