markused: fix generic method call mark (fix #24395) (#24399)

vlib/v/markused/walker.v

@@ -705,7 +705,8 @@ pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 	w.expr(node.left)
 	w.or_block(node.or_block)
 
-	fn_name := node.fkey()
+	mut fn_name := node.fkey()
+	mut receiver_typ := node.receiver_type
 	if w.used_fns[fn_name] {
 		return
 	}
@@ -735,12 +736,13 @@ pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 		&& !node.receiver_concrete_type.has_flag(.generic) {
 		// if receiver is generic, then cgen requires `node.receiver_type` to be T.
 		// We therefore need to get the concrete type from `node.receiver_concrete_type`.
-		fkey := '${int(node.receiver_concrete_type)}.${node.name}'
-		w.mark_fn_as_used(fkey)
+		fn_name = '${int(node.receiver_concrete_type)}.${node.name}'
+		receiver_typ = node.receiver_concrete_type
+		w.mark_fn_as_used(fn_name)
 	}
 	stmt := w.all_fns[fn_name] or { return }
 	if stmt.name == node.name {
-		if !node.is_method || node.receiver_type == stmt.receiver.typ {
+		if !node.is_method || receiver_typ == stmt.receiver.typ {
 			w.stmts(stmt.stmts)
 		}
 	}

vlib/v/tests/skip_unused/generic_call_from_json.vv

@@ -0,0 +1,36 @@
+import veb
+import x.json2
+
+pub struct Context {
+	veb.Context
+}
+
+pub struct App {
+	veb.Middleware[Context]
+}
+
+@['/'; POST]
+fn (app &App) index(mut ctx Context) veb.Result {
+	j := json2.raw_decode(ctx.req.data) or { return ctx.request_error('error') }
+
+	m := j.as_map()
+	myarr := m['myarr'] or { panic(error) }
+	m2 := myarr.arr()
+
+	for mc in m2 {
+		parts := mc.arr()
+
+		// Compiler error occurs here -->
+		first := parts[0].str()
+		second := parts[1].str()
+		third := parts[2].str()
+
+		println('1. ${first}, 2. ${second}, 3. ${third}')
+	}
+
+	return ctx.ok('ok')
+}
+
+fn main() {
+	_ := &App{}
+}