Improve pipeline expressions lexer

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

@@ -3,6 +3,8 @@ module Gitlab
     module Pipeline
       module Expression
         class Lexer
+          include ::Gitlab::Utils::StrongMemoize
+
           LEXEMES = [
             Expression::Lexeme::Variable,
             Expression::Lexeme::String,
@@ -10,34 +12,44 @@ module Gitlab
             Expression::Lexeme::Equals
           ].freeze
 
-          MAX_CYCLES = 5
           SyntaxError = Class.new(Statement::StatementError)
 
+          MAX_TOKENS = 100
+
           def initialize(statement)
             @scanner = StringScanner.new(statement)
-            @tokens = []
           end
 
-          def tokens
-            return @tokens if @tokens.any?
+          def tokens(max: MAX_TOKENS)
+            strong_memoize(:tokens) { tokenize(max) }
+          end
+
+          def lexemes
+            tokens.map(&:to_lexeme)
+          end
 
-            MAX_CYCLES.times do
-              LEXEMES.each do |lexeme|
+          private
+
+          def tokenize(max_tokens)
+            tokens = []
+
+            max_tokens.times do
               @scanner.skip(/\s+/) # ignore whitespace
 
-                lexeme.scan(@scanner).tap do |token|
-                  @tokens.push(token) if token.present?
-                end
+              return tokens if @scanner.eos?
 
-                return @tokens if @scanner.eos?
+              lexeme = LEXEMES.find do |type|
+                type.scan(@scanner).tap do |token|
+                  tokens.push(token) if token.present?
                 end
               end
 
-            raise Lexer::SyntaxError unless @scanner.eos?
+              unless lexeme.present?
+                raise Lexer::SyntaxError, 'Unknown lexeme found!'
+              end
             end
 
-          def lexemes
-            tokens.map(&:to_lexeme)
+            raise Lexer::SyntaxError, 'Too many tokens!'
           end
         end
       end

spec/lib/gitlab/ci/pipeline/expression/lexer_spec.rb

@@ -45,10 +45,10 @@ describe Gitlab::Ci::Pipeline::Expression::Lexer do
       expect(tokens.third.value).to eq '"text"'
     end
 
-    it 'limits statement to 5 tokens' do
+    it 'limits statement to specified amount of tokens' do
       lexer = described_class.new("$V1 $V2 $V3 $V4 $V5 $V6")
 
-      expect { lexer.tokens }
+      expect { lexer.tokens(max: 5) }
         .to raise_error described_class::SyntaxError
     end