added stack widget (SecondHalfGames#187)

* added stack widget

* fixed doc tests

crates/yakui-widgets/src/shorthand.rs

@@ -15,8 +15,8 @@ use crate::widgets::{
     ConstrainedBoxResponse, CountGrid, Divider, DividerResponse, Draggable, DraggableResponse,
     Flexible, FlexibleResponse, Image, ImageResponse, List, ListResponse, MaxWidth,
     MaxWidthResponse, NineSlice, Offset, OffsetResponse, Opaque, OpaqueResponse, Pad, PadResponse,
-    Reflow, ReflowResponse, Scrollable, ScrollableResponse, Slider, SliderResponse, Spacer, State,
-    StateResponse, Text, TextBox, TextBoxResponse, TextResponse,
+    Reflow, ReflowResponse, Scrollable, ScrollableResponse, Slider, SliderResponse, Spacer, Stack,
+    StackResponse, State, StateResponse, Text, TextBox, TextBoxResponse, TextResponse,
 };
 
 /// See [List].
@@ -192,6 +192,11 @@ pub fn max_width(max_width: f32, children: impl FnOnce()) -> Response<MaxWidthRe
     MaxWidth::new(max_width).show(children)
 }
 
+/// See [Stack].
+pub fn stack(children: impl FnOnce()) -> Response<StackResponse> {
+    Stack::new().show(children)
+}
+
 pub fn use_state<F, T: 'static>(default: F) -> Response<StateResponse<T>>
 where
     F: FnOnce() -> T + 'static,

crates/yakui-widgets/src/widgets/mod.rs

@@ -25,6 +25,7 @@ mod round_rect;
 mod scrollable;
 mod slider;
 mod spacer;
+mod stack;
 mod state;
 mod text;
 mod textbox;
@@ -58,6 +59,7 @@ pub use self::round_rect::*;
 pub use self::scrollable::*;
 pub use self::slider::*;
 pub use self::spacer::*;
+pub use self::stack::*;
 pub use self::state::*;
 pub use self::text::*;
 pub use self::textbox::*;

crates/yakui-widgets/src/widgets/stack.rs

@@ -0,0 +1,62 @@
+use yakui_core::{widget::Widget, Response};
+
+use crate::util::widget_children;
+
+/**
+A [Stack] widget. This widget does nothing interesting on its own, but
+when used "inside" other layouts, such as [List](crate::widgets::List),
+it will stacks its own children, rather than following the layout of its own parent.
+This internal layouting is just using yakui's default layout algorithm.
+
+Responds with [StackResponse].
+
+Shorthand:
+```rust
+# let _handle = yakui_widgets::DocTest::start();
+yakui::column(|| {
+    yakui::label("on top");
+    yakui::stack(|| {
+        // this would compose, by being stacked,
+        // to appear like "hello world", barring issues from spacing,
+        // as opposed to continuing the columnar layout setup above.
+        yakui::text(12.0, "hello");
+        yakui::text(12.0, "      world");
+    });
+    yakui::label("on bottom");
+});
+```
+*/
+#[derive(Debug, Default)]
+#[non_exhaustive]
+pub struct Stack {}
+
+impl Stack {
+    /// Creates a new [Stack].
+    pub fn new() -> Self {
+        Self {}
+    }
+
+    /// Shows the [Stack] along with its children.
+    pub fn show<F: FnOnce()>(self, children: F) -> Response<StackResponse> {
+        widget_children::<StackWidget, F>(children, self)
+    }
+}
+
+#[derive(Debug)]
+pub struct StackWidget;
+
+pub type StackResponse = ();
+
+impl Widget for StackWidget {
+    type Props<'a> = Stack;
+
+    type Response = StackResponse;
+
+    fn new() -> Self {
+        Self
+    }
+
+    fn update(&mut self, _props: Self::Props<'_>) -> Self::Response {
+        // nothing here
+    }
+}