Added BoxConstraints::UNBOUNDED. (#1126)

* BoxConstraints::UNBOUNDED is a constant that leaves the dimensions
  unconstrained
* Added tests confirming BoxConstraints::UNBOUNDED properties

Author: Daniel Dulaney

CHANGELOG.md

@@ -13,7 +13,8 @@ You can find its changes [documented below](#060---2020-06-01).
 - Export `Image` and `ImageData` by default. ([#1011] by [@covercash2])
 - Re-export `druid_shell::Scalable` under `druid` namespace. ([#1075] by [@ForLoveOfCats])
 - `TextBox` now supports ctrl and shift hotkeys. ([#1076] by [@vkahl])
-- Added selection text color to textbox. ([#1093] by [@sysint64])
+- Selection text color to textbox. ([#1093] by [@sysint64])
+- `BoxConstraints::UNBOUNDED` constant. ([#1126] by [@danieldulaney]) 
 - Close requests from the shell can now be intercepted ([#1118] by [@jneem])
 
 ### Changed
@@ -386,6 +387,7 @@ Last release without a changelog :(
 [#1118]: https://github.com/linebender/druid/pull/1118
 [#1119]: https://github.com/linebender/druid/pull/1119
 [#1120]: https://github.com/linebender/druid/pull/1120
+[#1126]: https://github.com/linebender/druid/pull/1120
 
 [Unreleased]: https://github.com/linebender/druid/compare/v0.6.0...master
 [0.6.0]: https://github.com/linebender/druid/compare/v0.5.0...v0.6.0

druid/src/box_constraints.rs

@@ -41,6 +41,14 @@ pub struct BoxConstraints {
 }
 
 impl BoxConstraints {
+    /// An unbounded box constraints object.
+    ///
+    /// Can be satisfied by any nonnegative size.
+    pub const UNBOUNDED: BoxConstraints = BoxConstraints {
+        min: Size::ZERO,
+        max: Size::new(f64::INFINITY, f64::INFINITY),
+    };
+
     /// Create a new box constraints object.
     ///
     /// Create constraints based on minimum and maximum size.
@@ -156,3 +164,16 @@ impl BoxConstraints {
         BoxConstraints::new(min, max)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn unbounded() {
+        assert!(!BoxConstraints::UNBOUNDED.is_width_bounded());
+        assert!(!BoxConstraints::UNBOUNDED.is_height_bounded());
+
+        assert_eq!(BoxConstraints::UNBOUNDED.min(), Size::ZERO);
+    }
+}