Extract pipeline expressions parser to a separate class

3 files changed, 35 insertions, 21 deletions

diff --git a/lib/gitlab/ci/pipeline/expression/lexer.rb b/lib/gitlab/ci/pipeline/expression/lexer.rb
index 1536374f0da..9334358cd8e 100644
--- a/lib/gitlab/ci/pipeline/expression/lexer.rb
+++ b/lib/gitlab/ci/pipeline/expression/lexer.rb
@@ -17,7 +17,9 @@ module Gitlab
             @tokens = []
           end
 
-          def tokenize
+          def tokens
+            return @tokens if @tokens.any?
+
             MAX_CYCLES.times do
               LEXEMES.each do |lexeme|
                 @scanner.skip(/\s+/) # ignore whitespace
@@ -32,6 +34,10 @@ module Gitlab
 
             raise Lexer::SyntaxError unless @scanner.eos?
           end
+
+          def lexemes
+            tokens.map(&:to_lexeme)
+          end
         end
       end
     end
diff --git a/lib/gitlab/ci/pipeline/expression/parser.rb b/lib/gitlab/ci/pipeline/expression/parser.rb
new file mode 100644
index 00000000000..f3201ec0979
--- /dev/null
+++ b/lib/gitlab/ci/pipeline/expression/parser.rb
@@ -0,0 +1,25 @@
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        class Parser
+          def initialize(syntax)
+            if syntax.is_a?(Expression::Lexer)
+              @tokens = syntax.tokens
+            else
+              @tokens = syntax.to_a
+            end
+          end
+
+          def tree
+            if @tokens.many?
+              Expression::Equals.new(@tokens.first.build, @tokens.last.build)
+            else
+              @tokens.first.build
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/pipeline/expression/statement.rb b/lib/gitlab/ci/pipeline/expression/statement.rb
index fabfcd0393d..e1e37f0f5cb 100644
--- a/lib/gitlab/ci/pipeline/expression/statement.rb
+++ b/lib/gitlab/ci/pipeline/expression/statement.rb
@@ -23,31 +23,14 @@ module Gitlab
             end
           end
 
-          def tokens
-            @tokens ||= @lexer.tokenize
-          end
-
-          def lexemes
-            @lexemes ||= tokens.map(&:to_lexeme)
-          end
-
-          ##
-          # Our syntax is very simple, so we don't yet need to implement a
-          # recursive parser, we can use the most simple approach to create
-          # a reverse descent parse tree "by hand".
-          #
           def parse_tree
-            raise StatementError if lexemes.empty?
+            raise StatementError if @lexer.lexemes.empty?
 
-            unless GRAMMAR.find { |syntax| syntax == lexemes }
+            unless GRAMMAR.find { |syntax| syntax == @lexer.lexemes }
               raise StatementError, 'Unknown pipeline expression!'
             end
 
-            if tokens.many?
-              Expression::Equals.new(tokens.first.build, tokens.last.build)
-            else
-              tokens.first.build
-            end
+            Expression::Parser.new(@lexer).tree
           end
 
           def evaluate