Add warning macro

spec/compiler/macro/macro_methods_spec.cr

@@ -1694,6 +1694,18 @@ module Crystal
         end
       end
 
+      describe "#warning" do
+        it "emits a warning at a specific node" do
+          assert_warning <<-CRYSTAL, "Oh noes"
+            macro test(node)
+              {% node.warning "Oh noes" %}
+            end
+
+            test 10
+          CRYSTAL
+        end
+      end
+
       it "executes instance_vars" do
         assert_macro("{{x.instance_vars.map &.stringify}}", %(["bytesize", "length", "c"])) do |program|
           {x: TypeNode.new(program.string)}
@@ -3066,6 +3078,18 @@ module Crystal
       assert_macro %({{compare_versions("1.10.3", "1.2.3")}}), %(1)
     end
 
+    describe "#warning" do
+      it "emits a top level warning" do
+        assert_warning <<-CRYSTAL, "Oh noes"
+          macro test
+            {% warning "Oh noes" %}
+          end
+
+          test
+        CRYSTAL
+      end
+    end
+
     describe "#parse_type" do
       it "path" do
         assert_type(%[class Bar; end; {{ parse_type("Bar").is_a?(Path) ? 1 : 'a'}}]) { int32 }

src/compiler/crystal/macros.cr

@@ -228,6 +228,10 @@ module Crystal::Macros
   def raise(message) : NoReturn
   end
 
+  # Emits a compile-time warning with the given *message*.
+  def warning(message : StringLiteral) : NilLiteral
+  end
+
   # Returns `true` if the given *filename* exists, `false` otherwise.
   def file_exists?(filename) : BoolLiteral
   end
@@ -413,11 +417,16 @@ module Crystal::Macros
     def !=(other : ASTNode) : BoolLiteral
     end
 
-    # Gives a compile-time error with the given *message*. This will
-    # highlight this node in the error message.
+    # Gives a compile-time error with the given *message*.
+    # This will highlight this node in the error message.
     def raise(message) : NoReturn
     end
 
+    # Emits a compile-time warning with the given *message*.
+    # This will highlight this node in the warning message.
+    def warning(message : StringLiteral) : NilLiteral
+    end
+
     # Returns `true` if this node's type is the given *type* or any of its
     # subclasses.
     #

src/compiler/crystal/macros/methods.cr

@@ -69,6 +69,8 @@ module Crystal
         interpret_system(node)
       when "raise"
         interpret_raise(node)
+      when "warning"
+        interpret_warning(node)
       when "file_exists?"
         interpret_file_exists?(node)
       when "read_file"
@@ -255,6 +257,10 @@ module Crystal
       macro_raise(node, node.args, self)
     end
 
+    def interpret_warning(node)
+      macro_warning(node, node.args, self)
+    end
+
     def interpret_file_exists?(node)
       interpret_check_args_toplevel do |arg|
         arg.accept self
@@ -382,6 +388,8 @@ module Crystal
         interpret_check_args { class_name }
       when "raise"
         macro_raise self, args, interpreter
+      when "warning"
+        macro_warning self, args, interpreter
       when "filename"
         interpret_check_args do
           filename = location.try &.original_filename
@@ -2678,6 +2686,18 @@ private def macro_raise(node, args, interpreter)
   node.raise msg, exception_type: Crystal::MacroRaiseException
 end
 
+private def macro_warning(node, args, interpreter)
+  msg = args.map do |arg|
+    arg.accept interpreter
+    interpreter.last.to_macro_id
+  end
+  msg = msg.join " "
+
+  interpreter.warnings.add_warning_at(node.location, msg)
+
+  Crystal::NilLiteral.new
+end
+
 private def empty_no_return_array
   Crystal::ArrayLiteral.new(of: Crystal::Path.global("NoReturn"))
 end