Support @[Deprecated] on annotation

spec/compiler/semantic/warnings_spec.cr

@@ -1,6 +1,64 @@
 require "../spec_helper"
 
 describe "Semantic: warnings" do
+  describe "deprecated aliases" do
+    it "detects deprecated aliases" do
+      assert_warning <<-CR,
+        struct SomeType; end
+
+        @[Deprecated]
+        alias OtherType = SomeType
+
+        OtherType.new
+        CR
+        "warning in line 4\nWarning: Deprecated alias OtherType."
+    end
+
+    it "detects deprecated namespaced aliases" do
+      assert_warning <<-CR,
+        struct SomeType; end
+
+        module MyNamespace
+          @[Deprecated]
+          alias OtherType = SomeType
+        end
+
+        MyNamespace::OtherType.new
+        CR
+        "warning in line 5\nWarning: Deprecated alias MyNamespace::OtherType."
+    end
+  end
+
+  describe "deprecated annotations" do
+    it "detects deprecated annotations" do
+      assert_warning <<-CR,
+        @[Deprecated]
+        annotation Foo; end
+
+        @[Foo]
+        def bar; end
+
+        bar
+        CR
+        "warning in line 2\nWarning: Deprecated annotation Foo."
+    end
+
+    it "detects deprecated namespaced annotations" do
+      assert_warning <<-CR,
+        module MyNamespace
+          @[Deprecated]
+          annotation Foo; end
+        end
+
+        @[MyNamespace::Foo]
+        def bar; end
+
+        bar
+        CR
+        "warning in line 3\nWarning: Deprecated annotation MyNamespace::Foo."
+    end
+  end
+
   describe "deprecated methods" do
     it "detects top-level deprecated methods" do
       assert_warning <<-CR,

src/compiler/crystal/semantic/ast.cr

@@ -675,9 +675,17 @@ module Crystal
   end
 
   class Alias
+    include Annotatable
+
     property! resolved_type : AliasType
   end
 
+  class AnnotationDef
+    include Annotatable
+
+    property! resolved_type : AnnotationType
+  end
+
   class External < Def
     property real_name : String
     property! fun_def : FunDef

src/compiler/crystal/semantic/cleanup_transformer.cr

@@ -126,6 +126,18 @@ module Crystal
       {@last_is_truthy, @last_is_falsey}
     end
 
+    def transform(node : Alias)
+      @program.check_call_to_deprecated_alias node
+
+      node
+    end
+
+    def transform(node : AnnotationDef)
+      @program.check_call_to_deprecated_annotation node
+
+      node
+    end
+
     def transform(node : Def)
       node.hook_expansions.try &.map! &.transform self
       node

src/compiler/crystal/semantic/top_level_visitor.cr

@@ -275,6 +275,11 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
   def visit(node : AnnotationDef)
     check_outside_exp node, "declare annotation"
 
+    annotations = read_annotations
+    process_annotations(annotations) do |annotation_type, ann|
+      node.add_annotation(annotation_type, ann)
+    end
+
     scope, name, type = lookup_type_def(node)
 
     if type
@@ -286,7 +291,9 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
       scope.types[name] = type
     end
 
-    attach_doc type, node, annotations: nil
+    node.resolved_type = type
+
+    attach_doc type, node, annotations
 
     false
   end
@@ -296,6 +303,10 @@ class Crystal::TopLevelVisitor < Crystal::SemanticVisitor
 
     annotations = read_annotations
 
+    process_annotations(annotations) do |annotation_type, ann|
+      node.add_annotation(annotation_type, ann)
+    end
+
     scope, name, existing_type = lookup_type_def(node)
 
     if existing_type

src/compiler/crystal/semantic/warnings.cr

@@ -8,6 +8,8 @@ module Crystal
     @deprecated_constants_detected = Set(String).new
     @deprecated_methods_detected = Set(String).new
     @deprecated_macros_detected = Set(String).new
+    @deprecated_aliases_detected = Set(String).new
+    @deprecated_annotations_detected = Set(String).new
 
     def check_deprecated_constant(const : Const, node : Path)
       return unless @warnings.level.all?
@@ -30,6 +32,18 @@ module Crystal
       end
     end
 
+    def check_call_to_deprecated_alias(node : Alias) : Nil
+      return unless @warnings.level.all?
+
+      check_deprecation(node, node.name, @deprecated_aliases_detected)
+    end
+
+    def check_call_to_deprecated_annotation(node : AnnotationDef) : Nil
+      return unless @warnings.level.all?
+
+      check_deprecation(node, node.name, @deprecated_aliases_detected)
+    end
+
     private def check_deprecation(object, use_site, detects)
       if (ann = object.annotation(self.deprecated_annotation)) &&
          (deprecated_annotation = DeprecatedAnnotation.from(ann))
@@ -59,6 +73,18 @@ module Crystal
     end
   end
 
+  class Alias
+    def short_reference
+      "alias #{resolved_type}"
+    end
+  end
+
+  class AnnotationDef
+    def short_reference
+      "annotation #{resolved_type}"
+    end
+  end
+
   class Macro
     def short_reference
       case owner