checker: fix declare assign literal with closure (#14544)

vlib/v/checker/assign.v

@@ -305,7 +305,7 @@ pub fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 				}
 			}
 		}
-		left_type_unwrapped := c.unwrap_generic(left_type)
+		left_type_unwrapped := c.unwrap_generic(ast.mktyp(left_type))
 		right_type_unwrapped := c.unwrap_generic(right_type)
 		if right_type_unwrapped == 0 {
 			// right type was a generic `T`

vlib/v/tests/assign_literal_with_closure_test.v

@@ -0,0 +1,26 @@
+fn sma(period int) fn (f64) f64 {
+	mut i := 0
+	mut sum := 0.0
+	mut storage := []f64{len: 0, cap: period}
+
+	return fn [mut storage, mut sum, mut i, period] (input f64) f64 {
+		if storage.len < period {
+			sum += input
+			storage << input
+		}
+
+		sum += input - storage[i]
+		storage[i], i = input, (i + 1) % period
+		return sum / f64(storage.len)
+	}
+}
+
+fn test_assign_literal_with_closure() {
+	sma3 := sma(3)
+	sma5 := sma(5)
+	println('x       sma3   sma5')
+	for x in [f64(1), 2, 3, 4, 5, 5, 4, 3, 2, 1] {
+		println('${x:5.3f}  ${sma3(x):5.3f}  ${sma5(x):5.3f}')
+	}
+	assert true
+}