Merge pull request #5114 from CocoaPods/seg-unknown-config-error

[Installer] List all found configurations when an unknown one is encountered

CHANGELOG.md

@@ -8,7 +8,10 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
 
 ##### Enhancements
 
-* None.  
+* When an unknown build configuration is mentioned in the Podfile, CocoaPods
+  will suggest the build configurations found in the user project.  
+  [Samuel Giddins](https://github.com/segiddins)
+  [CocoaPods#5113](https://github.com/CocoaPods/CocoaPods/issues/5113)
 
 ##### Bug Fixes
 

lib/cocoapods/installer.rb

@@ -249,7 +249,9 @@ module Pod
 
       remainder = whitelisted_configs - all_user_configurations
       unless remainder.empty?
-        raise Informative, "Unknown #{'configuration'.pluralize(remainder.size)} whitelisted: #{remainder.sort.to_sentence}."
+        raise Informative,
+              "Unknown #{'configuration'.pluralize(remainder.size)} whitelisted: #{remainder.sort.to_sentence}. " \
+              "CocoaPods found #{all_user_configurations.sort.to_sentence}, did you mean one of these?"
       end
     end