6 files changed, 86 insertions, 12 deletions
diff --git a/lib/gitlab/ci/pipeline/expression/lexeme/matches.rb b/lib/gitlab/ci/pipeline/expression/lexeme/matches.rb
new file mode 100644
index 00000000000..10957598f76
--- /dev/null
+++ b/lib/gitlab/ci/pipeline/expression/lexeme/matches.rb
@@ -0,0 +1,29 @@
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        module Lexeme
+          class Matches < Lexeme::Operator
+            PATTERN = /=~/.freeze
+
+            def initialize(left, right)
+              @left = left
+              @right = right
+            end
+
+            def evaluate(variables = {})
+              text = @left.evaluate(variables)
+              regexp = @right.evaluate(variables)
+
+              regexp.scan(text.to_s).any?
+            end
+
+            def self.build(_value, behind, ahead)
+              new(behind, ahead)
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb b/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb
new file mode 100644
index 00000000000..9b239c29ea4
--- /dev/null
+++ b/lib/gitlab/ci/pipeline/expression/lexeme/pattern.rb
@@ -0,0 +1,33 @@
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        module Lexeme
+          require_dependency 're2'
+
+          class Pattern < Lexeme::Value
+            PATTERN = %r{^/.+/[ismU]*$}.freeze
+
+            def initialize(regexp)
+              @value = regexp
+
+              unless Gitlab::UntrustedRegexp.valid?(@value)
+                raise Lexer::SyntaxError, 'Invalid regular expression!'
+              end
+            end
+
+            def evaluate(variables = {})
+              Gitlab::UntrustedRegexp.fabricate(@value)
+            rescue RegexpError
+              raise Expression::RuntimeError, 'Invalid regular expression!'
+            end
+
+            def self.build(string)
+              new(string)
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/ci/pipeline/expression/lexeme/string.rb b/lib/gitlab/ci/pipeline/expression/lexeme/string.rb
index 48bde213d44..346c92dc51e 100644
--- a/lib/gitlab/ci/pipeline/expression/lexeme/string.rb
+++ b/lib/gitlab/ci/pipeline/expression/lexeme/string.rb
@@ -4,7 +4,7 @@ module Gitlab
       module Expression
         module Lexeme
           class String < Lexeme::Value
-            PATTERN = /("(?<string>.+?)")|('(?<string>.+?)')/.freeze
+            PATTERN = /("(?<string>.*?)")|('(?<string>.*?)')/.freeze
 
             def initialize(value)
               @value = value
diff --git a/lib/gitlab/ci/pipeline/expression/lexeme/variable.rb b/lib/gitlab/ci/pipeline/expression/lexeme/variable.rb
index b781c15fd67..37643c8ef53 100644
--- a/lib/gitlab/ci/pipeline/expression/lexeme/variable.rb
+++ b/lib/gitlab/ci/pipeline/expression/lexeme/variable.rb
@@ -11,7 +11,7 @@ module Gitlab
             end
 
             def evaluate(variables = {})
-              HashWithIndifferentAccess.new(variables).fetch(@name, nil)
+              variables.with_indifferent_access.fetch(@name, nil)
             end
 
             def self.build(string)
diff --git a/lib/gitlab/ci/pipeline/expression/lexer.rb b/lib/gitlab/ci/pipeline/expression/lexer.rb
index e1c68b7c3c2..4cacb1e62c9 100644
--- a/lib/gitlab/ci/pipeline/expression/lexer.rb
+++ b/lib/gitlab/ci/pipeline/expression/lexer.rb
@@ -5,15 +5,17 @@ module Gitlab
         class Lexer
           include ::Gitlab::Utils::StrongMemoize
 
+          SyntaxError = Class.new(Expression::ExpressionError)
+
           LEXEMES = [
             Expression::Lexeme::Variable,
             Expression::Lexeme::String,
+            Expression::Lexeme::Pattern,
             Expression::Lexeme::Null,
-            Expression::Lexeme::Equals
+            Expression::Lexeme::Equals,
+            Expression::Lexeme::Matches
           ].freeze
 
-          SyntaxError = Class.new(Statement::StatementError)
-
           MAX_TOKENS = 100
 
           def initialize(statement, max_tokens: MAX_TOKENS)
diff --git a/lib/gitlab/ci/pipeline/expression/statement.rb b/lib/gitlab/ci/pipeline/expression/statement.rb
index 4f0e101b730..b36f1e0f865 100644
--- a/lib/gitlab/ci/pipeline/expression/statement.rb
+++ b/lib/gitlab/ci/pipeline/expression/statement.rb
@@ -3,23 +3,21 @@ module Gitlab
     module Pipeline
       module Expression
         class Statement
-          StatementError = Class.new(StandardError)
+          StatementError = Class.new(Expression::ExpressionError)
 
           GRAMMAR = [
+            %w[variable],
             %w[variable equals string],
             %w[variable equals variable],
             %w[variable equals null],
             %w[string equals variable],
             %w[null equals variable],
-            %w[variable]
+            %w[variable matches pattern]
           ].freeze
 
-          def initialize(statement, pipeline)
+          def initialize(statement, variables = {})
             @lexer = Expression::Lexer.new(statement)
-
-            @variables = pipeline.variables.map do |variable|
-              [variable.key, variable.value]
-            end
+            @variables = variables.with_indifferent_access
           end
 
           def parse_tree
@@ -35,6 +33,18 @@ module Gitlab
           def evaluate
             parse_tree.evaluate(@variables.to_h)
           end
+
+          def truthful?
+            evaluate.present?
+          rescue Expression::ExpressionError
+            false
+          end
+
+          def valid?
+            parse_tree.is_a?(Lexeme::Base)
+          rescue Expression::ExpressionError
+            false
+          end
         end
       end
     end