2 files changed, 27 insertions, 6 deletions

diff --git a/lib/gitlab/ci/variables/collection.rb b/lib/gitlab/ci/variables/collection.rb
index e2a8af9c26b..ef9ba1b73c7 100644
--- a/lib/gitlab/ci/variables/collection.rb
+++ b/lib/gitlab/ci/variables/collection.rb
@@ -24,6 +24,10 @@ module Gitlab
           self
         end
 
+        def compact
+          Collection.new(select { |variable| !variable.value.nil? })
+        end
+
         def concat(resources)
           return self if resources.nil?
 
@@ -64,11 +68,19 @@ module Gitlab
         end
 
         def expand_value(value, keep_undefined: false)
-          value.gsub(ExpandVariables::VARIABLES_REGEXP) do
+          value.gsub(Item::VARIABLES_REGEXP) do
             match = Regexp.last_match
-            result = @variables_by_key[match[1] || match[2]]&.value
-            result ||= match[0] if keep_undefined
-            result
+            if match[:key]
+              # we matched variable
+              if variable = @variables_by_key[match[:key]]
+                variable.value
+              elsif keep_undefined
+                match[0]
+              end
+            else
+              # we escape sequence
+              match[0]
+            end
           end
         end
 
diff --git a/lib/gitlab/ci/variables/collection/item.rb b/lib/gitlab/ci/variables/collection/item.rb
index 77da2c4cb91..0217e6129ca 100644
--- a/lib/gitlab/ci/variables/collection/item.rb
+++ b/lib/gitlab/ci/variables/collection/item.rb
@@ -7,6 +7,9 @@ module Gitlab
         class Item
           include Gitlab::Utils::StrongMemoize
 
+          VARIABLES_REGEXP = /\$\$|%%|\$(?<key>[a-zA-Z_][a-zA-Z0-9_]*)|\${\g<key>?}|%\g<key>%/.freeze.freeze
+          VARIABLE_REF_CHARS = %w[$ %].freeze
+
           def initialize(key:, value:, public: true, file: false, masked: false, raw: false)
             raise ArgumentError, "`#{key}` must be of type String or nil value, while it was: #{value.class}" unless
               value.is_a?(String) || value.nil?
@@ -34,9 +37,9 @@ module Gitlab
             strong_memoize(:depends_on) do
               next if raw
 
-              next unless ExpandVariables.possible_var_reference?(value)
+              next unless self.class.possible_var_reference?(value)
 
-              value.scan(ExpandVariables::VARIABLES_REGEXP).map(&:first)
+              value.scan(VARIABLES_REGEXP).filter_map(&:last)
             end
           end
 
@@ -64,6 +67,12 @@ module Gitlab
             end
           end
 
+          def self.possible_var_reference?(value)
+            return unless value
+
+            VARIABLE_REF_CHARS.any? { |symbol| value.include?(symbol) }
+          end
+
           def to_s
             return to_runner_variable.to_s unless depends_on