Run toString(null) for explicit nullable abstract

src/typing/calls.ml

@@ -322,7 +322,7 @@ let rec needs_temp_var e =
 	| TField (e, _) | TParenthesis e -> needs_temp_var e
 	| _ -> true
 
-let call_to_string ctx ?(resume=false) e =
+let call_to_string ctx ?(resume=false) ?(no_null_check=false) e =
 	if not ctx.allow_transform then
 		{ e with etype = ctx.t.tstring }
 	else
@@ -333,7 +333,7 @@ let call_to_string ctx ?(resume=false) e =
 		ctx.f.meta <- List.tl ctx.f.meta;
 		build_call ctx acc [] (WithType.with_type ctx.t.tstring) e.epos
 	in
-	if ctx.com.config.pf_static && not (is_nullable e.etype) then
+	if no_null_check || (ctx.com.config.pf_static && not (is_nullable e.etype)) then
 		gen_to_string e
 	else begin (* generate `if(e == null) 'null' else e.toString()` *)
 		let string_null = mk (TConst (TString "null")) ctx.t.tstring e.epos in

src/typing/operators.ml

@@ -197,8 +197,8 @@ let make_binop ctx op e1 e2 is_assign_op p =
 	let tstring = ctx.t.tstring in
 	let to_string e =
 		let rec loop t = match classify t with
-			| KAbstract ({a_impl = Some c},_) when PMap.mem "toString" c.cl_statics ->
-				call_to_string ctx e
+			| KAbstract ({a_impl = Some c; a_this},_) when PMap.mem "toString" c.cl_statics ->
+				call_to_string ~no_null_check:(is_explicit_null a_this) ctx e
 			| KInt | KFloat | KString -> e
 			| KUnk | KDyn | KNumParam _ | KStrParam _ | KOther ->
 				Texpr.Builder.resolve_and_make_static_call ctx.com.std "string" [e] e.epos

src/typing/typer.ml

@@ -1603,7 +1603,8 @@ and type_meta ?(mode=MGet) ctx m e1 with_type p =
 		| (Meta.ToString,_,_) ->
 			let e = e() in
 			(match follow e.etype with
-				| TAbstract({a_impl = Some c},_) when PMap.mem "toString" c.cl_statics -> call_to_string ctx e
+				| TAbstract({a_impl = Some c; a_this},_) when PMap.mem "toString" c.cl_statics ->
+					call_to_string ~no_null_check:(is_explicit_null a_this) ctx e
 				| _ -> e)
 		| (Meta.Markup,_,_) ->
 			raise_typing_error "Markup literals must be processed by a macro" p
@@ -1725,8 +1726,8 @@ and type_call_builtin ctx e el mode with_type p =
 			let e = type_expr ctx e WithType.value in
 			let infos = type_expr ctx infos WithType.value in
 			let e = match follow e.etype with
-				| TAbstract({a_impl = Some c},_) when PMap.mem "toString" c.cl_statics ->
-					call_to_string ctx e
+				| TAbstract({a_impl = Some c; a_this},_) when PMap.mem "toString" c.cl_statics ->
+					call_to_string ~no_null_check:(is_explicit_null a_this) ctx e
 				| _ ->
 					e
 			in

tests/unit/src/unit/issues/Issue12019.hx

@@ -0,0 +1,48 @@
+package unit.issues;
+
+private abstract MyStringA(Null<String>) from Null<String> {
+	function toString() {
+		if (this == null)
+			return "EMPTY";
+		return this;
+	}
+}
+
+private typedef NullableString = Null<String>;
+
+private abstract MyStringB(NullableString) from NullableString {
+	function toString() {
+		if (this == null)
+			return "EMPTY";
+		return this;
+	}
+}
+
+class Issue12019 extends unit.Test {
+	final a:MyStringA = null;
+	final b:MyStringB = null;
+
+	var oldTrace:(Dynamic, ?Null<haxe.PosInfos>) -> Void;
+
+	function setup() {
+		oldTrace = haxe.Log.trace;
+	}
+
+	function teardown() {
+		haxe.Log.trace = oldTrace;
+	}
+
+	function testTrace() {
+		haxe.Log.trace = function(v, ?infos) {
+			eq("EMPTY", v);
+		};
+
+		trace(a);
+		trace(b);
+	}
+
+	function testConcatenate() {
+		eq("Concatenated: EMPTY", "Concatenated: " + a);
+		eq("Concatenated: EMPTY", "Concatenated: " + b);
+	}
+}