impl Arbitrary for Text.

This is not quite up to final quality, because there are in fact some
numeric overflow panics. These need to be fixed, but for now I'm
restricting the generated range. Better to document them and start
fuzzing for _other_ problems than to hold off.

all-is-cubes/src/block.rs

@@ -733,7 +733,7 @@ mod arbitrary_block {
     // Manual impl because `GridPoint` doesn't impl Arbitrary.
     impl<'a> Arbitrary<'a> for Primitive {
         fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
-            Ok(match u.int_in_range(0..=3)? {
+            Ok(match u.int_in_range(0..=4)? {
                 0 => Primitive::Air,
                 1 => Primitive::Atom(Atom {
                     attributes: BlockAttributes::arbitrary(u)?,
@@ -748,6 +748,11 @@ mod arbitrary_block {
                     resolution: Resolution::arbitrary(u)?,
                     space: URef::arbitrary(u)?,
                 },
+                4 => Primitive::Text {
+                    text: text::Text::arbitrary(u)?,
+                    // TODO: fix unhandled overflows so this can be full i32 range
+                    offset: GridVector::from(<[i16; 3]>::arbitrary(u)?.map(i32::from)),
+                },
                 _ => unreachable!(),
             })
         }
@@ -768,6 +773,10 @@ mod arbitrary_block {
                         Resolution::size_hint(depth),
                         URef::<Space>::size_hint(depth),
                     ]),
+                    size_hint::and_all(&[
+                        text::Text::size_hint(depth),
+                        <[i16; 3]>::size_hint(depth),
+                    ]),
                 ])
             })
         }

all-is-cubes/src/block/text.rs

@@ -300,6 +300,45 @@ impl universe::VisitRefs for Text {
     }
 }
 
+#[cfg(feature = "arbitrary")]
+impl<'a> arbitrary::Arbitrary<'a> for Text {
+    fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
+        // As a temporary measure, restrict GridAab coordinate range to avoid overflows.
+        // Eventually we should fix the overflows, but let's do that after we build our own
+        // text rendering because that'll be easier.
+        // (Another possibility would be to actually restrict `layout_bounds` itself,)
+        let layout_bounds = GridAab::checked_from_lower_upper(
+            // euclid::Point3D doesn't implement Arbitrary (just an oversight apparently)
+            <[i16; 3]>::arbitrary(u)?.map(i32::from),
+            <[u16; 3]>::arbitrary(u)?.map(i32::from),
+        )
+        .map_err(|_volume_error| arbitrary::Error::IncorrectFormat)?;
+
+        Ok(Self {
+            // ArcStr doesn't implement Arbitrary
+            string: alloc::string::String::arbitrary(u)?.into(),
+            font: Font::arbitrary(u)?,
+            foreground: Block::arbitrary(u)?,
+            resolution: Resolution::arbitrary(u)?,
+            layout_bounds,
+            positioning: Positioning::arbitrary(u)?,
+        })
+    }
+
+    fn size_hint(depth: usize) -> (usize, Option<usize>) {
+        arbitrary::size_hint::recursion_guard(depth, |depth| {
+            arbitrary::size_hint::and_all(&[
+                alloc::string::String::size_hint(depth),
+                Font::size_hint(depth),
+                Block::size_hint(depth),
+                Resolution::size_hint(depth),
+                GridAab::size_hint(depth),
+                Positioning::size_hint(depth),
+            ])
+        })
+    }
+}
+
 impl TextBuilder {
     /// Converts this builder into a [`Text`] value.
     pub fn build(self) -> Text {
@@ -415,6 +454,7 @@ impl Default for TextBuilder {
 
 /// A font that may be used with [`Text`] blocks.
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[non_exhaustive]
 pub enum Font {
     /// A font whose characteristics are unspecified, other than that it is general-purpose and
@@ -449,6 +489,7 @@ impl universe::VisitRefs for Font {
 
 /// How a [`Text`] is to be positioned within a block.
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[allow(clippy::exhaustive_structs)] // TODO: probably want to do something else
 pub struct Positioning {
     /// How to place the text horizontally relative to the anchor point.
@@ -475,6 +516,7 @@ pub struct Positioning {
 ///
 /// A component of [`Positioning`].
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[non_exhaustive]
 pub enum PositioningX {
     // TODO: Distinguish 'end of graphic' (last bit of ink) from 'nominal character spacing'?
@@ -498,6 +540,7 @@ pub enum PositioningX {
 ///
 /// A component of [`Positioning`].
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[non_exhaustive]
 pub enum PositioningY {
     /// The top of a line of text (past which no voxels extend) is aligned with the top edge
@@ -523,6 +566,7 @@ pub enum PositioningY {
 ///
 /// A component of [`Positioning`].
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[non_exhaustive]
 pub enum PositioningZ {
     /// Against the back (negative Z) face of the layout bounds.