Do not use keyword args to pass expression variables

lib/gitlab/ci/pipeline/expression/lexeme/equals.rb

@@ -11,7 +11,7 @@ module Gitlab
               @right = right
             end
 
-            def evaluate(**variables)
+            def evaluate(variables = {})
               @left.evaluate(variables) == @right.evaluate(variables)
             end
 

lib/gitlab/ci/pipeline/expression/lexeme/null.rb

@@ -10,7 +10,7 @@ module Gitlab
               @value = nil
             end
 
-            def evaluate(**_)
+            def evaluate(variables = {})
               nil
             end
 

lib/gitlab/ci/pipeline/expression/lexeme/string.rb

@@ -10,7 +10,7 @@ module Gitlab
               @value = value
             end
 
-            def evaluate(**_)
+            def evaluate(variables = {})
               @value.to_s
             end
 

lib/gitlab/ci/pipeline/expression/lexeme/variable.rb

@@ -10,8 +10,8 @@ module Gitlab
               @name = name
             end
 
-            def evaluate(**variables)
-              variables[@name.to_sym]
+            def evaluate(variables = {})
+              HashWithIndifferentAccess.new(variables).fetch(@name, nil)
             end
 
             def self.build(string)

lib/gitlab/ci/pipeline/expression/statement.rb

@@ -18,7 +18,7 @@ module Gitlab
             @lexer = Expression::Lexer.new(statement)
 
             @variables = pipeline.variables.map do |variable|
-              [variable.key.to_sym, variable.value]
+              [variable.key, variable.value]
             end
           end
 

spec/lib/gitlab/ci/pipeline/expression/lexeme/variable_spec.rb

@@ -22,6 +22,13 @@ describe Gitlab::Ci::Pipeline::Expression::Lexeme::Variable do
         .to eq 'my variable'
     end
 
+    it 'allows to use a string as a variable key too' do
+      variable = described_class.new('VARIABLE')
+
+      expect(variable.evaluate('VARIABLE' => 'my variable'))
+        .to eq 'my variable'
+    end
+
     it 'returns nil if it is not defined' do
       variable = described_class.new('VARIABLE')