fix compilation of panic_on_bad_st_as.vv

vlib/v/markused/markused.v

@@ -523,6 +523,9 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 	if table.used_features.range_index {
 		walker.fn_by_name(string_idx_str + '.substr')
 	}
+	if walker.as_cast_type_names.len > 0 {
+		walker.fn_by_name('new_array_from_c_array')
+	}
 
 	table.used_features.used_fns = walker.used_fns.move()
 	table.used_features.used_consts = walker.used_consts.move()

vlib/v/markused/walker.v

@@ -22,6 +22,8 @@ mut:
 	all_fns     map[string]ast.FnDecl
 	all_consts  map[string]ast.ConstField
 	all_globals map[string]ast.GlobalField
+	//
+	as_cast_type_names map[string]string
 }
 
 pub fn Walker.new(params Walker) &Walker {
@@ -511,6 +513,7 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 		///
 		ast.AsCast {
 			w.expr(node.expr)
+			w.as_cast(node)
 		}
 		ast.AtExpr {}
 		ast.BoolLiteral {}
@@ -730,3 +733,27 @@ pub fn (mut w Walker) or_block(node ast.OrExpr) {
 		w.stmts(node.stmts)
 	}
 }
+
+pub fn (mut w Walker) as_cast(node ast.AsCast) {
+	if node.typ.has_flag(.generic) || node.expr_type.has_flag(.generic) {
+		w.as_cast_type_names['some_generic_type'] = 'some_generic_name'
+		return
+	}
+	mut expr_type_sym := w.table.sym(node.expr_type)
+	if mut expr_type_sym.info is ast.SumType {
+		w.fill_as_cast_type_names(expr_type_sym.info.variants)
+	} else if mut expr_type_sym.info is ast.Interface && node.expr_type != node.typ {
+		w.fill_as_cast_type_names(expr_type_sym.info.types)
+	}
+}
+
+fn (mut w Walker) fill_as_cast_type_names(types []ast.Type) {
+	for variant in types {
+		idx := u32(variant).str()
+		if idx in w.as_cast_type_names {
+			continue
+		}
+		variant_sym := w.table.sym(variant)
+		w.as_cast_type_names[idx] = variant_sym.name
+	}
+}