checker: fix generics struct init in generic fn (fix #15080) (#15088)

vlib/v/checker/struct.v

@@ -303,6 +303,13 @@ pub fn (mut c Checker) struct_init(mut node ast.StructInit) ast.Type {
 			c.error('unknown struct: $type_sym.name', node.pos)
 			return ast.void_type
 		}
+		.any {
+			// `T{ foo: 22 }`
+			for mut field in node.fields {
+				field.typ = c.expr(field.expr)
+				field.expected_type = field.typ
+			}
+		}
 		// string & array are also structs but .kind of string/array
 		.struct_, .string, .array, .alias {
 			mut info := ast.Struct{}

vlib/v/tests/generics_struct_init_in_generic_fn_test.v

@@ -0,0 +1,25 @@
+module main
+
+pub struct Person {
+pub mut:
+	id int
+}
+
+fn test_generics_struct_init_in_generic_fn() {
+	leo := Person{
+		id: 1
+	}
+	println(leo)
+	assert leo.id == 1
+
+	ret := do(leo)
+	println(ret)
+	assert ret.id == 2
+}
+
+pub fn do<T>(t T) T {
+	max := T{
+		id: 2
+	}
+	return max
+}