Count an exhaustive case's complexity as 1

spec/ameba/ast/visitors/counting_visitor_spec.cr

@@ -44,14 +44,33 @@ module Ameba::AST
         visitor.count.should eq 1
       end
 
+      it "increases count for every exhaustive case" do
+        code = %(
+          def hello(a : Int32 | Int64 | Float32 | Float64)
+            case a
+            in Int32 then "int32"
+            in Int64 then "int64"
+            in Float32 then "float32"
+            in Float64 then "float64"
+            end
+          end
+        )
+        node = Crystal::Parser.new(code).parse
+        visitor = CountingVisitor.new node
+        visitor.count.should eq 2
+      end
+
       {% for pair in [
                        {code: "if true; end", description: "conditional"},
                        {code: "while true; end", description: "while loop"},
                        {code: "until 1 < 2; end", description: "until loop"},
                        {code: "begin; rescue; end", description: "rescue"},
-                       {code: "case 1 when 1; end", description: "when"},
                        {code: "true || false", description: "or"},
                        {code: "true && false", description: "and"},
+                       {
+                         code:        "a : String | Int32 = 1; case a when true; end",
+                         description: "inexhaustive when",
+                       },
                      ] %}
         it "increases count for every {{ pair[:description].id }}" do
           node = Crystal::Parser.new("def hello; {{ pair[:code].id }} end").parse

src/ameba/ast/visitors/counting_visitor.cr

@@ -23,13 +23,22 @@ module Ameba::AST
     # Uses the same logic than rubocop. See
     # https://github.com/rubocop-hq/rubocop/blob/master/lib/rubocop/cop/metrics/cyclomatic_complexity.rb#L21
     # Except "for", because crystal doesn't have a "for" loop.
-    {% for node in %i(if while until rescue when or and) %}
+    {% for node in %i(if while until rescue or and) %}
       # :nodoc:
       def visit(node : Crystal::{{ node.id.capitalize }})
         @complexity += 1 unless macro_condition
       end
     {% end %}
 
+    # :nodoc:
+    def visit(node : Crystal::Case)
+      # Count the complexity of an exhaustive `Case` as 1
+      # Otherwise count the number of `When`s
+      case_complexity = node.exhaustive? ? 1 : node.whens.size
+      @complexity += case_complexity unless macro_condition
+      true
+    end
+
     def visit(node : Crystal::MacroIf | Crystal::MacroFor)
       @macro_condition = true
       @complexity = DEFAULT_COMPLEXITY