Add a workaround for https://github.com/crystal-lang/crystal/pull/6032

spec/ameba/ast/branch_spec.cr

@@ -121,18 +121,16 @@ module Ameba::AST
       end
 
       context "Crystal::Case" do
-        # FIXME:
-        # https://github.com/crystal-lang/crystal/pull/6032
-        # it "constructs a branch in cond" do
-        #   branch = branch_of_assign_in_def %(
-        #     def method(a)
-        #       case (a = 2)
-        #       when true then nil
-        #       end
-        #     end
-        #   )
-        #   branch.to_s.should eq "(a = 2)"
-        # end
+        it "constructs a branch in cond" do
+          branch = branch_of_assign_in_def %(
+            def method(a)
+              case (a = 2)
+              when true then nil
+              end
+            end
+          )
+          branch.to_s.should eq "(a = 2)"
+        end
 
         it "constructs a branch in when" do
           branch = branch_of_assign_in_def %(

spec/ameba/rule/unused_argument_spec.cr

@@ -137,6 +137,17 @@ module Ameba::Rule
       subject.catch(s).should be_valid
     end
 
+    it "doesn't report if arg if referenced in case" do
+      s = Source.new %(
+        def foo(a)
+          case a
+          when /foo/
+          end
+        end
+      )
+      subject.catch(s).should be_valid
+    end
+
     context "super" do
       it "reports if variable is not referenced implicitly by super" do
         s = Source.new %(

spec/ameba/rule/useless_assign_spec.cr

@@ -582,6 +582,18 @@ module Ameba::Rule
           s.errors.first.location.to_s.should eq ":5:17"
           s.errors.last.location.to_s.should eq ":7:17"
         end
+
+        it "doesn't report if assignment is referenced in cond" do
+          s = Source.new %(
+            def method
+              a = 2
+              case a
+              when /foo/
+              end
+            end
+          )
+          subject.catch(s).should be_valid
+        end
       end
 
       context "binary operator" do

src/ameba.cr

@@ -2,6 +2,7 @@ require "./ameba/*"
 require "./ameba/ast/**"
 require "./ameba/rule/*"
 require "./ameba/formatter/*"
+require "./ameba/support/*"
 
 # Ameba's entry module.
 #

src/ameba/support/ast.cr

@@ -0,0 +1,12 @@
+{% if Crystal::VERSION == "0.24.2" %}
+  # workaround for https://github.com/crystal-lang/crystal/pull/6032
+  module Crystal
+    class Case < ASTNode
+      def accept_children(visitor)
+        @cond.try &.accept visitor
+        @whens.each &.accept visitor
+        @else.try &.accept visitor
+      end
+    end
+  end
+{% end %}