Add parenthesis support for if: conditions

This extends RPN to support `()` in expressions

changelogs/unreleased/support-parentheses-in-conditions.yml

+---
+title: 'Add parenthesis support for if: conditions'
+merge_request: 37574
+author:
+type: added

doc/ci/variables/README.md

@@ -742,6 +742,40 @@ Precedence of operators follows the
 [Ruby 2.5 standard](https://ruby-doc.org/core-2.5.0/doc/syntax/precedence_rdoc.html),
 so `&&` is evaluated before `||`.
 
+#### Parentheses
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/230938) in GitLab 13.3
+
+It is possible to use parentheses to group conditions. Parentheses have the highest
+precedence of all operators. Expressions enclosed in parentheses are evaluated first,
+and the result is used for the rest of the expression.
+
+Many nested parentheses can be used to create complex conditions, and the inner-most
+expressions in parentheses are evaluated first. For an expression to be valid an equal
+number of `(` and `)` need to be used.
+
+Examples:
+
+- `($VARIABLE1 =~ /^content.*/ || $VARIABLE2) && ($VARIABLE3 =~ /thing$/ || $VARIABLE4)`
+- `($VARIABLE1 =~ /^content.*/ || $VARIABLE2 =~ /thing$/) && $VARIABLE3`
+- `$CI_COMMIT_BRANCH == "my-branch" || (($VARIABLE1 == "thing" || $VARIABLE2 == "thing") && $VARIABLE3)`
+
+The feature is currently deployed behind a feature flag that is **disabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../administration/feature_flags.md)
+can opt to enable it for your instance.
+
+To enable it:
+
+```ruby
+Feature.enable(:ci_if_parenthesis_enabled)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:ci_if_parenthesis_enabled)
+```
+
 ### Storing regular expressions in variables
 
 It is possible to store a regular expression in a variable, to be used for pattern matching:

lib/gitlab/ci/features.rb

@@ -70,6 +70,10 @@ module Gitlab
         ::Feature.enabled?(:ci_bulk_insert_on_create, project, default_enabled: true)
       end
 
+      def self.ci_if_parenthesis_enabled?
+        ::Feature.enabled?(:ci_if_parenthesis_enabled)
+      end
+
       def self.allow_to_create_merge_request_pipelines_in_target_project?(target_project)
         ::Feature.enabled?(:ci_allow_to_create_merge_request_pipelines_in_target_project, target_project, default_enabled: true)
       end

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

@@ -5,7 +5,7 @@ module Gitlab
     module Pipeline
       module Expression
         module Lexeme
-          class And < Lexeme::Operator
+          class And < Lexeme::LogicalOperator
             PATTERN = /&&/.freeze
 
             def evaluate(variables = {})

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

@@ -10,6 +10,10 @@ module Gitlab
               raise NotImplementedError
             end
 
+            def name
+              self.class.name.demodulize.underscore
+            end
+
             def self.build(token)
               raise NotImplementedError
             end
@@ -23,6 +27,10 @@ module Gitlab
             def self.pattern
               self::PATTERN
             end
+
+            def self.consume?(lexeme)
+              lexeme && precedence >= lexeme.precedence
+            end
           end
         end
       end

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

@@ -5,7 +5,7 @@ module Gitlab
     module Pipeline
       module Expression
         module Lexeme
-          class Equals < Lexeme::Operator
+          class Equals < Lexeme::LogicalOperator
             PATTERN = /==/.freeze
 
             def evaluate(variables = {})

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

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        module Lexeme
+          class LogicalOperator < Lexeme::Operator
+            # This operator class is design to handle single operators that take two
+            # arguments. Expression::Parser was originally designed to read infix operators,
+            # and so the two operands are called "left" and "right" here. If we wish to
+            # implement an Operator that takes a greater or lesser number of arguments, a
+            # structural change or additional Operator superclass will likely be needed.
+
+            def initialize(left, right)
+              raise OperatorError, 'Invalid left operand' unless left.respond_to? :evaluate
+              raise OperatorError, 'Invalid right operand' unless right.respond_to? :evaluate
+
+              @left = left
+              @right = right
+            end
+
+            def inspect
+              "#{name}(#{@left.inspect}, #{@right.inspect})"
+            end
+
+            def self.type
+              :logical_operator
+            end
+          end
+        end
+      end
+    end
+  end
+end

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

@@ -5,7 +5,7 @@ module Gitlab
     module Pipeline
       module Expression
         module Lexeme
-          class Matches < Lexeme::Operator
+          class Matches < Lexeme::LogicalOperator
             PATTERN = /=~/.freeze
 
             def evaluate(variables = {})

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

@@ -5,7 +5,7 @@ module Gitlab
     module Pipeline
       module Expression
         module Lexeme
-          class NotEquals < Lexeme::Operator
+          class NotEquals < Lexeme::LogicalOperator
             PATTERN = /!=/.freeze
 
             def evaluate(variables = {})

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

@@ -5,7 +5,7 @@ module Gitlab
     module Pipeline
       module Expression
         module Lexeme
-          class NotMatches < Lexeme::Operator
+          class NotMatches < Lexeme::LogicalOperator
             PATTERN = /\!~/.freeze
 
             def evaluate(variables = {})

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

@@ -9,13 +9,17 @@ module Gitlab
             PATTERN = /null/.freeze
 
             def initialize(value = nil)
-              @value = nil
+              super
             end
 
             def evaluate(variables = {})
               nil
             end
 
+            def inspect
+              'null'
+            end
+
             def self.build(_value)
               self.new
             end

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

@@ -6,24 +6,10 @@ module Gitlab
       module Expression
         module Lexeme
           class Operator < Lexeme::Base
-            # This operator class is design to handle single operators that take two
-            # arguments. Expression::Parser was originally designed to read infix operators,
-            # and so the two operands are called "left" and "right" here. If we wish to
-            # implement an Operator that takes a greater or lesser number of arguments, a
-            # structural change or additional Operator superclass will likely be needed.
-
             OperatorError = Class.new(Expression::ExpressionError)
 
-            def initialize(left, right)
-              raise OperatorError, 'Invalid left operand' unless left.respond_to? :evaluate
-              raise OperatorError, 'Invalid right operand' unless right.respond_to? :evaluate
-
-              @left = left
-              @right = right
-            end
-
             def self.type
-              :operator
+              raise NotImplementedError
             end
 
             def self.precedence

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

@@ -5,7 +5,7 @@ module Gitlab
     module Pipeline
       module Expression
         module Lexeme
-          class Or < Lexeme::Operator
+          class Or < Lexeme::LogicalOperator
             PATTERN = /\|\|/.freeze
 
             def evaluate(variables = {})

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

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        module Lexeme
+          class ParenthesisClose < Lexeme::Operator
+            PATTERN = /\)/.freeze
+
+            def self.type
+              :parenthesis_close
+            end
+
+            def self.precedence
+              900
+            end
+          end
+        end
+      end
+    end
+  end
+end

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

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Pipeline
+      module Expression
+        module Lexeme
+          class ParenthesisOpen < Lexeme::Operator
+            PATTERN = /\(/.freeze
+
+            def self.type
+              :parenthesis_open
+            end
+
+            def self.precedence
+              # Needs to be higher than `ParenthesisClose` and all other Lexemes
+              901
+            end
+          end
+        end
+      end
+    end
+  end
+end

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

@@ -11,7 +11,7 @@ module Gitlab
             PATTERN = %r{^\/([^\/]|\\/)+[^\\]\/[ismU]*}.freeze
 
             def initialize(regexp)
-              @value = regexp.gsub(/\\\//, '/')
+              super(regexp.gsub(/\\\//, '/'))
 
               unless Gitlab::UntrustedRegexp::RubySyntax.valid?(@value)
                 raise Lexer::SyntaxError, 'Invalid regular expression!'
@@ -24,6 +24,10 @@ module Gitlab
               raise Expression::RuntimeError, 'Invalid regular expression!'
             end
 
+            def inspect
+              "/#{value}/"
+            end
+
             def self.pattern
               PATTERN
             end

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

@@ -9,13 +9,17 @@ module Gitlab
             PATTERN = /("(?<string>.*?)")|('(?<string>.*?)')/.freeze
 
             def initialize(value)
-              @value = value
+              super(value)
             end
 
             def evaluate(variables = {})
               @value.to_s
             end
 
+            def inspect
+              @value.inspect
+            end
+
             def self.build(string)
               new(string.match(PATTERN)[:string])
             end

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

@@ -9,6 +9,10 @@ module Gitlab
             def self.type
               :value
             end
+
+            def initialize(value)
+              @value = value
+            end
           end
         end
       end

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

@@ -8,12 +8,12 @@ module Gitlab
           class Variable < Lexeme::Value
             PATTERN = /\$(?<name>\w+)/.freeze
 
-            def initialize(name)
-              @name = name
+            def evaluate(variables = {})
+              variables.with_indifferent_access.fetch(@value, nil)
             end
 
-            def evaluate(variables = {})
-              variables.with_indifferent_access.fetch(@name, nil)
+            def inspect
+              "$#{@value}"
             end
 
             def self.build(string)

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

@@ -10,6 +10,8 @@ module Gitlab
           SyntaxError = Class.new(Expression::ExpressionError)
 
           LEXEMES = [
+            Expression::Lexeme::ParenthesisOpen,
+            Expression::Lexeme::ParenthesisClose,
             Expression::Lexeme::Variable,
             Expression::Lexeme::String,
             Expression::Lexeme::Pattern,
@@ -22,6 +24,28 @@ module Gitlab
             Expression::Lexeme::Or
           ].freeze
 
+          # To be removed with `ci_if_parenthesis_enabled`
+          LEGACY_LEXEMES = [
+            Expression::Lexeme::Variable,
+            Expression::Lexeme::String,
+            Expression::Lexeme::Pattern,
+            Expression::Lexeme::Null,
+            Expression::Lexeme::Equals,
+            Expression::Lexeme::Matches,
+            Expression::Lexeme::NotEquals,
+            Expression::Lexeme::NotMatches,
+            Expression::Lexeme::And,
+            Expression::Lexeme::Or
+          ].freeze
+
+          def self.lexemes
+            if ::Gitlab::Ci::Features.ci_if_parenthesis_enabled?
+              LEXEMES
+            else
+              LEGACY_LEXEMES
+            end
+          end
+
           MAX_TOKENS = 100
 
           def initialize(statement, max_tokens: MAX_TOKENS)
@@ -47,7 +71,7 @@ module Gitlab
 
               return tokens if @scanner.eos?
 
-              lexeme = LEXEMES.find do |type|
+              lexeme = self.class.lexemes.find do |type|
                 type.scan(@scanner).tap do |token|
                   tokens.push(token) if token.present?
                 end

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

@@ -15,11 +15,18 @@ module Gitlab
           def tree
             results = []
 
-            tokens_rpn.each do |token|
+            tokens =
+              if ::Gitlab::Ci::Features.ci_if_parenthesis_enabled?
+                tokens_rpn
+              else
+                legacy_tokens_rpn
+              end
+
+            tokens.each do |token|
               case token.type
               when :value
                 results.push(token.build)
-              when :operator
+              when :logical_operator
                 right_operand = results.pop
                 left_operand  = results.pop
 
@@ -27,7 +34,7 @@ module Gitlab
                   results.push(res)
                 end
               else
-                raise ParseError, 'Unprocessable token found in parse tree'
+                raise ParseError, "Unprocessable token found in parse tree: #{token.type}"
               end
             end
 
@@ -45,6 +52,7 @@ module Gitlab
 
           # Parse the expression into Reverse Polish Notation
           # (See: Shunting-yard algorithm)
+          # Taken from: https://en.wikipedia.org/wiki/Shunting-yard_algorithm#The_algorithm_in_detail
           def tokens_rpn
             output = []
             operators = []
@@ -53,7 +61,34 @@ module Gitlab
               case token.type
               when :value
                 output.push(token)
-              when :operator
+              when :logical_operator
+                output.push(operators.pop) while token.lexeme.consume?(operators.last&.lexeme)
+
+                operators.push(token)
+              when :parenthesis_open
+                operators.push(token)
+              when :parenthesis_close
+                output.push(operators.pop) while token.lexeme.consume?(operators.last&.lexeme)
+
+                raise ParseError, 'Unmatched parenthesis' unless operators.last
+
+                operators.pop if operators.last.lexeme.type == :parenthesis_open
+              end
+            end
+
+            output.concat(operators.reverse)
+          end
+
+          # To be removed with `ci_if_parenthesis_enabled`
+          def legacy_tokens_rpn
+            output = []
+            operators = []
+
+            @tokens.each do |token|
+              case token.type
+              when :value
+                output.push(token)
+              when :logical_operator
                 if operators.any? && token.lexeme.precedence >= operators.last.lexeme.precedence
                   output.push(operators.pop)
                 end

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

@@ -24,7 +24,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexeme::And do
 
   describe '.type' do
     it 'is an operator' do
-      expect(described_class.type).to eq :operator
+      expect(described_class.type).to eq :logical_operator
     end
   end
 

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

@@ -27,7 +27,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexeme::Equals do
 
   describe '.type' do
     it 'is an operator' do
-      expect(described_class.type).to eq :operator
+      expect(described_class.type).to eq :logical_operator
     end
   end
 

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

@@ -28,7 +28,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexeme::Matches do
 
   describe '.type' do
     it 'is an operator' do
-      expect(described_class.type).to eq :operator
+      expect(described_class.type).to eq :logical_operator
     end
   end
 

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

@@ -27,7 +27,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexeme::NotEquals do
 
   describe '.type' do
     it 'is an operator' do
-      expect(described_class.type).to eq :operator
+      expect(described_class.type).to eq :logical_operator
     end
   end
 

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

@@ -28,7 +28,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexeme::NotMatches do
 
   describe '.type' do
     it 'is an operator' do
-      expect(described_class.type).to eq :operator
+      expect(described_class.type).to eq :logical_operator
     end
   end
 

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

@@ -24,7 +24,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexeme::Or do
 
   describe '.type' do
     it 'is an operator' do
-      expect(described_class.type).to eq :operator
+      expect(described_class.type).to eq :logical_operator
     end
   end
 

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

@@ -81,6 +81,35 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Lexer do
       with_them do
         it { is_expected.to eq(tokens) }
       end
+
+      context 'with parentheses are used' do
+        where(:expression, :tokens) do
+          '($PRESENT_VARIABLE =~ /my var/) && $EMPTY_VARIABLE =~ /nope/' | ['(', '$PRESENT_VARIABLE', '=~', '/my var/', ')', '&&', '$EMPTY_VARIABLE', '=~', '/nope/']
+          '$PRESENT_VARIABLE =~ /my var/ || ($EMPTY_VARIABLE =~ /nope/)' | ['$PRESENT_VARIABLE', '=~', '/my var/', '||', '(', '$EMPTY_VARIABLE', '=~', '/nope/', ')']
+          '($PRESENT_VARIABLE && (null || $EMPTY_VARIABLE == ""))'       | ['(', '$PRESENT_VARIABLE', '&&', '(', 'null', '||', '$EMPTY_VARIABLE', '==', '""', ')', ')']
+        end
+
+        with_them do
+          context 'when ci_if_parenthesis_enabled is enabled' do
+            before do
+              stub_feature_flags(ci_if_parenthesis_enabled: true)
+            end
+
+            it { is_expected.to eq(tokens) }
+          end
+
+          context 'when ci_if_parenthesis_enabled is disabled' do
+            before do
+              stub_feature_flags(ci_if_parenthesis_enabled: false)
+            end
+
+            it do
+              expect { subject }
+                .to raise_error described_class::SyntaxError
+            end
+          end
+        end
+      end
     end
   end
 

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

 # frozen_string_literal: true
 
-require 'fast_spec_helper'
+require 'spec_helper'
 
 RSpec.describe Gitlab::Ci::Pipeline::Expression::Parser do
+  before do
+    stub_feature_flags(ci_if_parenthesis_enabled: true)
+  end
+
   describe '#tree' do
-    context 'when using two operators' do
-      it 'returns a reverse descent parse tree' do
-        expect(described_class.seed('$VAR1 == "123"').tree)
-          .to be_a Gitlab::Ci::Pipeline::Expression::Lexeme::Equals
+    context 'validates simple operators' do
+      using RSpec::Parameterized::TableSyntax
+
+      where(:expression, :result_tree) do
+        '$VAR1 == "123"' | 'equals($VAR1, "123")'
+        '$VAR1 == "123" == $VAR2' | 'equals(equals($VAR1, "123"), $VAR2)'
+        '$VAR' | '$VAR'
+        '"some value"' | '"some value"'
+        'null' | 'null'
+        '$VAR1 || $VAR2 && $VAR3' | 'or($VAR1, and($VAR2, $VAR3))'
+        '$VAR1 && $VAR2 || $VAR3' | 'or(and($VAR1, $VAR2), $VAR3)'
+        '$VAR1 && $VAR2 || $VAR3 && $VAR4' | 'or(and($VAR1, $VAR2), and($VAR3, $VAR4))'
+        '$VAR1 && ($VAR2 || $VAR3) && $VAR4' | 'and(and($VAR1, or($VAR2, $VAR3)), $VAR4)'
+      end
+
+      with_them do
+        it { expect(described_class.seed(expression).tree.inspect).to eq(result_tree) }
       end
     end
 
-    context 'when using three operators' do
-      it 'returns a reverse descent parse tree' do
-        expect(described_class.seed('$VAR1 == "123" == $VAR2').tree)
-          .to be_a Gitlab::Ci::Pipeline::Expression::Lexeme::Equals
+    context 'when combining && and OR operators' do
+      subject { described_class.seed('$VAR1 == "a" || $VAR2 == "b" && $VAR3 == "c" || $VAR4 == "d" && $VAR5 == "e"').tree }
+
+      context 'when parenthesis engine is enabled' do
+        before do
+          stub_feature_flags(ci_if_parenthesis_enabled: true)
+        end
+
+        it 'returns operations in a correct order' do
+          expect(subject.inspect)
+            .to eq('or(or(equals($VAR1, "a"), and(equals($VAR2, "b"), equals($VAR3, "c"))), and(equals($VAR4, "d"), equals($VAR5, "e")))')
         end
       end
 
-    context 'when using a single variable token' do
-      it 'returns a single token instance' do
-        expect(described_class.seed('$VAR').tree)
-          .to be_a Gitlab::Ci::Pipeline::Expression::Lexeme::Variable
+      context 'when parenthesis engine is disabled (legacy)' do
+        before do
+          stub_feature_flags(ci_if_parenthesis_enabled: false)
         end
+
+        it 'returns operations in a invalid order' do
+          expect(subject.inspect)
+            .to eq('or(equals($VAR1, "a"), and(equals($VAR2, "b"), or(equals($VAR3, "c"), and(equals($VAR4, "d"), equals($VAR5, "e")))))')
+        end
+      end
+    end
+
+    context 'when using parenthesis' do
+      subject { described_class.seed('(($VAR1 == "a" || $VAR2 == "b") && $VAR3 == "c" || $VAR4 == "d") && $VAR5 == "e"').tree }
+
+      before do
+        stub_feature_flags(ci_if_parenthesis_enabled: true)
       end
 
-    context 'when using a single string token' do
-      it 'returns a single token instance' do
-        expect(described_class.seed('"some value"').tree)
-          .to be_a Gitlab::Ci::Pipeline::Expression::Lexeme::String
+      it 'returns operations in a correct order' do
+        expect(subject.inspect)
+          .to eq('and(or(and(or(equals($VAR1, "a"), equals($VAR2, "b")), equals($VAR3, "c")), equals($VAR4, "d")), equals($VAR5, "e"))')
       end
     end
 
     context 'when expression is empty' do
-      it 'returns a null token' do
+      it 'raises a parsing error' do
         expect { described_class.seed('').tree }
           .to raise_error Gitlab::Ci::Pipeline::Expression::Parser::ParseError
       end
     end
 
-    context 'when expression is null' do
-      it 'returns a null token' do
-        expect(described_class.seed('null').tree)
-          .to be_a Gitlab::Ci::Pipeline::Expression::Lexeme::Null
-      end
-    end
-
     context 'when two value tokens have no operator' do
       it 'raises a parsing error' do
         expect { described_class.seed('$VAR "text"').tree }
@@ -66,5 +94,42 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Parser do
             .to raise_error Gitlab::Ci::Pipeline::Expression::Lexeme::Operator::OperatorError
       end
     end
+
+    context 'when parenthesis are unmatched' do
+      context 'when parenthesis engine is enabled' do
+        before do
+          stub_feature_flags(ci_if_parenthesis_enabled: true)
+        end
+
+        where(:expression) do
+          [
+            '$VAR == (',
+            '$VAR2 == ("aa"',
+            '$VAR2 == ("aa"))',
+            '$VAR2 == "aa")',
+            '(($VAR2 == "aa")',
+            '($VAR2 == "aa"))'
+          ]
+        end
+
+        with_them do
+          it 'raises a ParseError' do
+            expect { described_class.seed(expression).tree }
+              .to raise_error Gitlab::Ci::Pipeline::Expression::Parser::ParseError
+          end
+        end
+      end
+
+      context 'when parenthesis engine is disabled' do
+        before do
+          stub_feature_flags(ci_if_parenthesis_enabled: false)
+        end
+
+        it 'raises an SyntaxError' do
+          expect { described_class.seed('$VAR == (').tree }
+            .to raise_error Gitlab::Ci::Pipeline::Expression::Lexer::SyntaxError
+        end
+      end
+    end
   end
 end

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

 # frozen_string_literal: true
 
-require 'fast_spec_helper'
-require 'rspec-parameterized'
+require 'spec_helper'
 
 RSpec.describe Gitlab::Ci::Pipeline::Expression::Statement do
   subject do
@@ -109,6 +108,17 @@ RSpec.describe Gitlab::Ci::Pipeline::Expression::Statement do
       '$UNDEFINED_VARIABLE || $PRESENT_VARIABLE'                   | 'my variable'
       '$UNDEFINED_VARIABLE == null || $PRESENT_VARIABLE'           | true
       '$PRESENT_VARIABLE || $UNDEFINED_VARIABLE == null'           | 'my variable'
+
+      '($PRESENT_VARIABLE)'                                        | 'my variable'
+      '(($PRESENT_VARIABLE))'                                      | 'my variable'
+      '(($PRESENT_VARIABLE && null) || $EMPTY_VARIABLE == "")'     | true
+      '($PRESENT_VARIABLE) && (null || $EMPTY_VARIABLE == "")'     | true
+      '("string" || "test") == "string"'                           | true
+      '(null || ("test" == "string"))'                             | false
+      '("string" == ("test" && "string"))'                         | true
+      '("string" == ("test" || "string"))'                         | false
+      '("string" == "test" || "string")'                           | "string"
+      '("string" == ("string" || (("1" == "1") && ("2" == "3"))))' | true
     end
 
     with_them do