1 files changed, 43 insertions, 0 deletions
diff --git a/lib/rubygems/errors.rb b/lib/rubygems/errors.rb
index 8304647546..f607d14938 100644
--- a/lib/rubygems/errors.rb
+++ b/lib/rubygems/errors.rb
@@ -20,6 +20,49 @@ module Gem
     attr_accessor :requirement
   end
 
+  ##
+  # Raised when trying to activate a gem, and that gem does not exist on the
+  # system.  Instead of rescuing from this class, make sure to rescue from the
+  # superclass Gem::LoadError to catch all types of load errors.
+  class MissingSpecError < Gem::LoadError
+    def initialize name, requirement
+      @name        = name
+      @requirement = requirement
+    end
+
+    def message # :nodoc:
+      build_message +
+        "Checked in 'GEM_PATH=#{Gem.path.join(File::PATH_SEPARATOR)}', execute `gem env` for more information"
+    end
+
+    private
+
+    def build_message
+      total = Gem::Specification.stubs.size
+      "Could not find '#{name}' (#{requirement}) among #{total} total gem(s)\n"
+    end
+  end
+
+  ##
+  # Raised when trying to activate a gem, and the gem exists on the system, but
+  # not the requested version. Instead of rescuing from this class, make sure to
+  # rescue from the superclass Gem::LoadError to catch all types of load errors.
+  class MissingSpecVersionError < MissingSpecError
+    attr_reader :specs
+
+    def initialize name, requirement, specs
+      super(name, requirement)
+      @specs = specs
+    end
+
+    private
+
+    def build_message
+      names = specs.map(&:full_name)
+      "Could not find '#{name}' (#{requirement}) - did find: [#{names.join ','}]\n"
+    end
+  end
+
   # Raised when there are conflicting gem specs loaded
 
   class ConflictError < LoadError