checker: fix f: app.method field initialisation, for fn fields, ini…

…tialised with generic methods (#22665)

vlib/v/checker/checker.v

@@ -1696,15 +1696,15 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 		}
 		return field.typ
 	}
-	if mut method := sym.find_method_with_generic_parent(field_name) {
+	if mut method := c.table.sym(c.unwrap_generic(typ)).find_method_with_generic_parent(field_name) {
 		if c.expected_type != 0 && c.expected_type != ast.none_type {
 			fn_type := ast.new_type(c.table.find_or_register_fn_type(method, false, true))
 			// if the expected type includes the receiver, don't hide it behind a closure
 			if c.check_types(fn_type, c.expected_type) {
 				return fn_type
 			}
 		}
-		receiver := method.params[0].typ
+		receiver := c.unwrap_generic(method.params[0].typ)
 		if receiver.nr_muls() > 0 {
 			if !c.inside_unsafe {
 				rec_sym := c.table.sym(receiver.set_nr_muls(0))
@@ -1723,7 +1723,7 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 		node.has_hidden_receiver = true
 		method.name = ''
 		fn_type := ast.new_type(c.table.find_or_register_fn_type(method, false, true))
-		node.typ = fn_type
+		node.typ = c.unwrap_generic(fn_type)
 		return fn_type
 	}
 	if sym.kind !in [.struct, .aggregate, .interface, .sum_type] {

vlib/v/gen/c/cgen.v

@@ -4028,7 +4028,7 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 				return
 			}
 			receiver := m.params[0]
-			expr_styp := g.styp(node.expr_type.idx_type())
+			expr_styp := g.styp(g.unwrap_generic(node.expr_type).idx_type())
 			data_styp := g.styp(receiver.typ.idx_type())
 			mut sb := strings.new_builder(256)
 			name := '_V_closure_${expr_styp}_${m.name}_${node.pos.pos}'

vlib/v/tests/selector_generic_fn_test.v

@@ -0,0 +1,24 @@
+struct Struct {
+	f fn (f64) f64 = unsafe { nil }
+}
+
+struct App {}
+
+pub fn (mut a App) frame(dt f64) f64 {
+	dump(voidptr(a))
+	dump(dt)
+	return dt
+}
+
+fn generic_f[T](mut ctx T) ! {
+	s := Struct{
+		f: unsafe { ctx.frame }
+	}
+	assert s.f(1.2) == 1.2
+}
+
+fn test_main() {
+	mut app := &App{}
+	generic_f(mut app)!
+	assert true
+}