Emit badge when DeprecatedAnnotation is applied

src/compiler/crystal/tools/doc/constant.cr

@@ -38,4 +38,8 @@ class Crystal::Doc::Constant
       builder.field "summary", formatted_summary
     end
   end
+
+  def annotations(annotation_type)
+    @const.annotations(annotation_type)
+  end
 end

src/compiler/crystal/tools/doc/generator.cr

@@ -300,6 +300,7 @@ class Crystal::Doc::Generator
 
   def doc(context, string)
     string = isolate_flag_lines string
+    string += build_flag_lines_from_annotations context
     markdown = String.build do |io|
       Markdown.parse string, MarkdownDocRenderer.new(context, io)
     end
@@ -343,6 +344,19 @@ class Crystal::Doc::Generator
     end
   end
 
+  def build_flag_lines_from_annotations(context)
+    first = true
+    String.build do |io|
+      if anns = context.annotations(@program.deprecated_annotation)
+        anns.each do |ann|
+          io << "\n\n" if first
+          first = false
+          io << "DEPRECATED: #{DeprecatedAnnotation.from(ann).message}\n\n"
+        end
+      end
+    end
+  end
+
   def compute_repository
     # check whether inside git work-tree
     `git rev-parse --is-inside-work-tree >/dev/null 2>&1`

src/compiler/crystal/tools/doc/macro.cr

@@ -139,4 +139,9 @@ class Crystal::Doc::Macro
       builder.field "def", self.macro
     end
   end
+
+  def annotations(annotation_type)
+    # macros does not support annotations
+    nil
+  end
 end

src/compiler/crystal/tools/doc/method.cr

@@ -223,4 +223,8 @@ class Crystal::Doc::Method
       builder.field "def", self.def
     end
   end
+
+  def annotations(annotation_type)
+    @def.annotations(annotation_type)
+  end
 end

src/compiler/crystal/tools/doc/type.cr

@@ -837,4 +837,8 @@ class Crystal::Doc::Type
       builder.field "name", name
     end
   end
+
+  def annotations(annotation_type)
+    @type.annotations(annotation_type)
+  end
 end