Add AST::Util#nodoc?(node) helper method

spec/ameba/ast/util_spec.cr

@@ -354,6 +354,50 @@ module Ameba::AST
       end
     end
 
+    describe "#nodoc?" do
+      it "returns true if a node has a single `:nodoc:` annotation" do
+        node = as_node <<-CRYSTAL, wants_doc: true
+          # :nodoc:
+          def foo; end
+          CRYSTAL
+
+        subject.nodoc?(node).should be_true
+      end
+
+      it "returns true if a node has a `:nodoc:` annotation in the first line" do
+        node = as_node <<-CRYSTAL, wants_doc: true
+          # :nodoc:
+          #
+          # foo
+          def foo; end
+          CRYSTAL
+
+        subject.nodoc?(node).should be_true
+      end
+
+      it "returns true if a node has a `:nodoc:` annotation in the last line" do
+        node = as_node <<-CRYSTAL, wants_doc: true
+          # foo
+          #
+          # :nodoc:
+          def foo; end
+          CRYSTAL
+
+        subject.nodoc?(node).should be_true
+      end
+
+      it "returns false if a node has a `:nodoc:` annotation in the middle" do
+        node = as_node <<-CRYSTAL, wants_doc: true
+          # foo
+          # :nodoc:
+          # bar
+          def foo; end
+          CRYSTAL
+
+        subject.nodoc?(node).should be_false
+      end
+    end
+
     describe "#control_exp_code" do
       it "returns the exp code of a control expression" do
         s = "return 1"

src/ameba/ast/util.cr

@@ -194,6 +194,18 @@ module Ameba::AST::Util
     end
   end
 
+  # Returns `true` if node has a `:nodoc:` annotation as
+  # the first or the last line.
+  def nodoc?(node)
+    return false unless node.responds_to?(:doc)
+    return false unless doc = node.doc.presence
+
+    lines = doc.lines.map!(&.strip)
+
+    lines.first? == ":nodoc:" ||
+      lines.last? == ":nodoc:"
+  end
+
   # Returns the exp code of a control expression.
   # Wraps implicit tuple literal with curly brackets (e.g. multi-return).
   def control_exp_code(node : Crystal::ControlExpression, code_lines)