Fix doc comment above annotation with macro expansion

spec/compiler/semantic/doc_spec.cr

@@ -632,5 +632,47 @@ describe "Semantic: doc" do
       type = program.lookup_macros("foo").as(Array(Macro)).first
       type.doc.should eq("Some description")
     end
+
+    it "attached to macro call" do
+      result = semantic %(
+        annotation Ann
+        end
+
+        macro gen_type
+          class Foo; end
+        end
+
+        # Some description
+        @[Ann]
+        gen_type
+      ), wants_doc: true
+      program = result.program
+      type = program.types["Foo"]
+      type.doc.should eq("Some description")
+    end
+
+    it "attached to macro call that produces multiple types" do
+      result = semantic %(
+        annotation Ann
+        end
+
+        class Foo
+          macro getter(decl)
+            @{{decl.var.id}} : {{decl.type.id}}
+
+            def {{decl.var.id}} : {{decl.type.id}}
+              @{{decl.var.id}}
+            end
+          end
+
+          # Some description
+          @[Ann]
+          getter name : String?
+        end
+      ), wants_doc: true
+      program = result.program
+      a_def = program.types["Foo"].lookup_defs("name").first
+      a_def.doc.should eq("Some description")
+    end
   end
 end

src/compiler/crystal/semantic/semantic_visitor.cr

@@ -364,6 +364,8 @@ abstract class Crystal::SemanticVisitor < Crystal::Visitor
       visibility: visibility,
     )
 
+    node.doc ||= annotations_doc @annotations
+
     if node_doc = node.doc
       generated_nodes.accept PropagateDocVisitor.new(node_doc)
     end
@@ -525,6 +527,10 @@ abstract class Crystal::SemanticVisitor < Crystal::Visitor
     end
   end
 
+  private def annotations_doc(annotations)
+    annotations.try(&.first?).try &.doc
+  end
+
   def check_class_var_annotations
     thread_local = false
     process_annotations(@annotations) do |annotation_type, ann|