Support Ruby 2.7's pattern match for Layout/ElseAlignment cop

CHANGELOG.md

@@ -8,6 +8,7 @@
 * [#7654](https://github.com/rubocop-hq/rubocop/issues/7654): Support `with_fixed_indentation` option for `Layout/ArrayAlignment` cop. ([@nikitasakov][])
 * [#7783](https://github.com/rubocop-hq/rubocop/pull/7783): Support Ruby 2.7's numbered parameter for `Style/RedundantSort`. ([@koic][])
 * [#7795](https://github.com/rubocop-hq/rubocop/issues/7795): Make `Layout/EmptyLineAfterGuardClause` aware of case where `and` or `or` is used before keyword that break control (e.g. `and return`). ([@koic][])
+* [#7786](https://github.com/rubocop-hq/rubocop/pull/7786): Support Ruby 2.7's pattern match for `Layout/ElseAlignment` cop. ([@koic][])
 
 ### Bug fixes
 

lib/rubocop.rb

@@ -37,6 +37,7 @@
 require_relative 'rubocop/ast/node/array_node'
 require_relative 'rubocop/ast/node/block_node'
 require_relative 'rubocop/ast/node/break_node'
+require_relative 'rubocop/ast/node/case_match_node'
 require_relative 'rubocop/ast/node/case_node'
 require_relative 'rubocop/ast/node/class_node'
 require_relative 'rubocop/ast/node/def_node'

lib/rubocop/ast/builder.rb

@@ -21,6 +21,7 @@ class Builder < Parser::Builders::Default
         array:        ArrayNode,
         block:        BlockNode,
         break:        BreakNode,
+        case_match:   CaseMatchNode,
         case:         CaseNode,
         class:        ClassNode,
         def:          DefNode,

lib/rubocop/ast/node/case_match_node.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module AST
+    # A node extension for `case_match` nodes. This will be used in place of
+    # a plain node when the builder constructs the AST, making its methods
+    # available to all `case_match` nodes within RuboCop.
+    class CaseMatchNode < Node
+      include ConditionalNode
+
+      # Returns the keyword of the `case` statement as a string.
+      #
+      # @return [String] the keyword of the `case` statement
+      def keyword
+        'case'
+      end
+
+      # Calls the given block for each `in_pattern` node in the `in` statement.
+      # If no block is given, an `Enumerator` is returned.
+      #
+      # @return [self] if a block is given
+      # @return [Enumerator] if no block is given
+      def each_in_pattern
+        return in_pattern_branches.to_enum(__method__) unless block_given?
+
+        in_pattern_branches.each do |condition|
+          yield condition
+        end
+
+        self
+      end
+
+      # Returns an array of all the when branches in the `case` statement.
+      #
+      # @return [Array<Node>] an array of `in_pattern` nodes
+      def in_pattern_branches
+        node_parts[1...-1]
+      end
+
+      # Returns the else branch of the `case` statement, if any.
+      #
+      # @return [Node] the else branch node of the `case` statement
+      # @return [nil] if the case statement does not have an else branch.
+      def else_branch
+        node_parts[-1]
+      end
+
+      # Checks whether this case statement has an `else` branch.
+      #
+      # @return [Boolean] whether the `case` statement has an `else` branch
+      def else?
+        !loc.else.nil?
+      end
+    end
+  end
+end

lib/rubocop/ast/traversal.rb

@@ -21,7 +21,7 @@ def walk(node)
                              arg restarg blockarg shadowarg
                              kwrestarg zsuper lambda redo retry
                              forward_args forwarded_args
-                             match_var match_nil_pattern].freeze
+                             match_var match_nil_pattern empty_else].freeze
       ONE_CHILD_NODE    = %i[splat kwsplat block_pass not break next
                              preexe postexe match_current_line defined?
                              arg_expr pin match_rest if_guard unless_guard
@@ -31,7 +31,7 @@ def walk(node)
                              undef alias args super yield or and
                              while_post until_post iflipflop eflipflop
                              match_with_lvasgn begin kwbegin return
-                             in_match case_match in_pattern match_alt
+                             in_match match_alt
                              match_as array_pattern array_pattern_with_tail
                              hash_pattern const_pattern].freeze
       SECOND_CHILD_ONLY = %i[lvasgn ivasgn cvasgn gvasgn optarg kwarg
@@ -178,13 +178,15 @@ def on_case(node)
         nil
       end
 
-      alias on_rescue  on_case
-      alias on_resbody on_case
-      alias on_ensure  on_case
-      alias on_for     on_case
-      alias on_when    on_case
-      alias on_irange  on_case
-      alias on_erange  on_case
+      alias on_rescue     on_case
+      alias on_resbody    on_case
+      alias on_ensure     on_case
+      alias on_for        on_case
+      alias on_when       on_case
+      alias on_case_match on_case
+      alias on_in_pattern on_case
+      alias on_irange     on_case
+      alias on_erange     on_case
 
       def on_numblock(node)
         children = node.children

lib/rubocop/cop/layout/else_alignment.rb

@@ -59,6 +59,14 @@ def on_case(node)
           check_alignment(node.when_branches.last.loc.keyword, node.loc.else)
         end
 
+        def on_case_match(node)
+          return unless node.else?
+
+          check_alignment(
+            node.in_pattern_branches.last.loc.keyword, node.loc.else
+          )
+        end
+
         def autocorrect(node)
           AlignmentCorrector.correct(processed_source, node, column_delta)
         end

spec/rubocop/ast/case_match_node_spec.rb

@@ -0,0 +1,130 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::AST::CaseMatchNode do
+  let(:case_match_node) { parse_source(source).ast }
+
+  context 'when using Ruby 2.7 or newer', :ruby27 do
+    describe '.new' do
+      let(:source) do
+        <<~RUBY
+          case expr
+          in pattern
+          end
+        RUBY
+      end
+
+      it { expect(case_match_node.is_a?(described_class)).to be(true) }
+    end
+
+    describe '#keyword' do
+      let(:source) do
+        <<~RUBY
+          case expr
+          in pattern
+          end
+        RUBY
+      end
+
+      it { expect(case_match_node.keyword).to eq('case') }
+    end
+
+    describe '#in_pattern_branches' do
+      let(:source) do
+        <<~RUBY
+          case expr
+          in pattern
+          in pattern
+          in pattern
+          end
+        RUBY
+      end
+
+      it { expect(case_match_node.in_pattern_branches.size).to eq(3) }
+      it {
+        expect(case_match_node.in_pattern_branches).to all(be_in_pattern_type)
+      }
+    end
+
+    describe '#each_in_pattern' do
+      let(:source) do
+        <<~RUBY
+          case expr
+          in pattern
+          in pattern
+          in pattern
+          end
+        RUBY
+      end
+
+      context 'when not passed a block' do
+        it {
+          expect(case_match_node.each_in_pattern.is_a?(Enumerator)).to be(true)
+        }
+      end
+
+      context 'when passed a block' do
+        it 'yields all the conditions' do
+          expect { |b| case_match_node.each_in_pattern(&b) }
+            .to yield_successive_args(*case_match_node.in_pattern_branches)
+        end
+      end
+    end
+
+    describe '#else?' do
+      context 'without an else statement' do
+        let(:source) do
+          <<~RUBY
+            case expr
+            in pattern
+            end
+          RUBY
+        end
+
+        it { expect(case_match_node.else?).to be(false) }
+      end
+
+      context 'with an else statement' do
+        let(:source) do
+          <<~RUBY
+            case expr
+            in pattern
+            else
+            end
+          RUBY
+        end
+
+        it { expect(case_match_node.else?).to be(true) }
+      end
+    end
+
+    describe '#else_branch' do
+      describe '#else?' do
+        context 'without an else statement' do
+          let(:source) do
+            <<~RUBY
+              case expr
+              in pattern
+              end
+            RUBY
+          end
+
+          it { expect(case_match_node.else_branch.nil?).to be(true) }
+        end
+
+        context 'with an else statement' do
+          let(:source) do
+            <<~RUBY
+              case expr
+              in pattern
+              else
+                :foo
+              end
+            RUBY
+          end
+
+          it { expect(case_match_node.else_branch.sym_type?).to be(true) }
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/layout/else_alignment_spec.rb

@@ -359,6 +359,64 @@
       RUBY
     end
 
+    context '>= Ruby 2.7', :ruby27 do
+      context 'with case match' do
+        it 'registers an offense for misaligned else' do
+          expect_offense(<<~RUBY)
+            case 0
+            in 0
+              foo
+            in -1..1
+              bar
+            in Integer
+              baz
+             else
+             ^^^^ Align `else` with `in`.
+              qux
+            end
+          RUBY
+        end
+
+        it 'accepts correctly aligned case/when/else' do
+          expect_no_offenses(<<~RUBY)
+            case 0
+            in 0
+              foo
+            in -1..1
+              bar
+            in Integer
+              baz
+            else
+              qux
+            end
+          RUBY
+        end
+
+        it 'accepts correctly aligned empty else' do
+          expect_no_offenses(<<~RUBY)
+            case 0
+            in 0
+              foo
+            in -1..1
+              bar
+            in Integer
+              baz
+            else
+            end
+          RUBY
+        end
+
+        it 'accepts case match without else' do
+          expect_no_offenses(<<~'RUBY')
+            case 0
+            in a
+              p a
+            end
+          RUBY
+        end
+      end
+    end
+
     it 'accepts else aligned with when but not with case' do
       # "Indent when as deep as case" is the job of another cop, and this is
       # one of the possible styles supported by configuration.