Support negative numbers in cubic-bezier(...) function

CHANGELOG.md

@@ -7,6 +7,10 @@ All notable changes to this project are documented in this file.
 
  * Fixed missing items compilation error in the generated code related to public functions (#2655).
 
+### Slint Language
+
+- Support negative numbers in `cubic-bezier(...)` function.
+
 ### Rust
 
 - Added `slint::Image::load_from_svg_data(buffer: &[u8])` to load SVGs from memory.

internal/compiler/builtin_macros.rs

@@ -28,6 +28,8 @@ pub fn lower_macro(
         BuiltinMacroFunction::Debug => debug_macro(n, sub_expr.collect(), diag),
         BuiltinMacroFunction::CubicBezier => {
             let mut has_error = None;
+            let expected_argument_type_error =
+                "Arguments to cubic bezier curve must be number literal";
             // FIXME: this is not pretty to be handling there.
             // Maybe "cubic_bezier" should be a function that is lowered later
             let mut a = || match sub_expr.next() {
@@ -36,11 +38,16 @@ pub fn lower_macro(
                     0.
                 }
                 Some((Expression::NumberLiteral(val, Unit::None), _)) => val as f32,
+                // handle negative numbers
+                Some((Expression::UnaryOp { sub, op: '-' }, n)) => match *sub {
+                    Expression::NumberLiteral(val, Unit::None) => (-1.0 * val) as f32,
+                    _ => {
+                        has_error.get_or_insert((n, expected_argument_type_error));
+                        0.
+                    }
+                },
                 Some((_, n)) => {
-                    has_error.get_or_insert((
-                        n,
-                        "Arguments to cubic bezier curve must be number literal",
-                    ));
+                    has_error.get_or_insert((n, expected_argument_type_error));
                     0.
                 }
             };

tests/cases/types/cubic-bezier.slint

@@ -0,0 +1,10 @@
+// Copyright © SixtyFPS GmbH <info@slint-ui.com>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial
+
+// Test that cubic-bezier() can accept negative numbers
+
+TestCase := Rectangle {
+    animate background {
+      easing: cubic-bezier(0.600, -0.280, 0.735, 0.045); // ease-in-back
+    }
+}