Feat: Add valid-range-aware int shrinker

This enables having shinking that is kept within the range
given to generator, so shrinker, for example, avoids shrinking
to zero if zero is regarded as out of range in given property.

- Refactor: Simplify the int decrement iterator.
  The iterator is used in int shrinking, and did before have
  knowledge of it being used togheter with eager shrink
  iterator. Simplify decrement shrinker by having the logic
  for not repeating some values to the eager iterator instead.

- Deprecate old `shrink::int()`, and refer to use of either
  `shrink::int_in_range` for updated use or
  `shrink::int_to_zero` for old behaviour.

- Let shrinker emit candidates on both sides of target
  value, in essence trying out more candidates before giving
  up.

README.md

@@ -64,12 +64,12 @@ and shrinkers for:
 
 Other known limitations:
 
-* For now, integer and float generators do not limit them self to shrink to
+* For now, float generators do not limit them self to shrink to
   values within given generator range, but will by default shrink toward zero.
   For instance, let say that we create generator
-  `monkey_test::gen::i64::ranged(10..100)`, the associated shrinker will not
-  only try candidates withing the given range `10..100`, but can also try other
-  values like -10 and will ultimately try to shrink toward zero.
+  `monkey_test::gen::f64::ranged(10.0..100.0)`, the associated shrinker will not
+  only try candidates withing the given range `10.0..100.0`, but can also try other
+  values like -10.0 and will ultimately try to shrink toward zero.
 
 For details on recent changes, see the [CHANGELOG](CHANGELOG.md).
 

src/gen/integer.rs

@@ -13,7 +13,7 @@ use std::ops::RangeBounds;
 /// value zero, if in range of given bounds.
 pub fn ranged<E, B>(bounds: B) -> BoxGen<E>
 where
-    E: PrimInt + SampleUniform + 'static + std::fmt::Debug,
+    E: PrimInt + SampleUniform + std::fmt::Debug + 'static,
     B: RangeBounds<E>,
 {
     let min = start(&bounds);
@@ -34,7 +34,7 @@ where
 /// name, since `ranged` should be preferred.
 pub fn completely_random<E, B>(bounds: B) -> BoxGen<E>
 where
-    E: PrimInt + SampleUniform + 'static,
+    E: PrimInt + SampleUniform + std::fmt::Debug + 'static,
     B: RangeBounds<E>,
 {
     let min = start(&bounds);
@@ -44,7 +44,7 @@ where
         let distr = rand::distributions::Uniform::new_inclusive(min, max);
         rand_chacha::ChaCha8Rng::seed_from_u64(seed).sample_iter(distr)
     })
-    .with_shrinker(crate::shrink::int())
+    .with_shrinker(crate::shrink::int_in_range(min, max))
 }
 
 fn start<E, B>(bounds: &B) -> E
@@ -108,6 +108,6 @@ mod tests {
 
     #[test]
     fn has_shrinker() {
-        assert_generator_can_shrink(super::ranged(..10), 123);
+        assert_generator_can_shrink(super::ranged(..1000), 123);
     }
 }

src/gen/mix.rs

@@ -180,13 +180,13 @@ mod test {
     #[test]
     fn mix_should_reuse_shrinker_from_first_generator() {
         let with_shrinker = super::mix_evenly(&[
-            crate::gen::u8::any().with_shrinker(crate::shrink::int()),
+            crate::gen::u8::any().with_shrinker(crate::shrink::int_to_zero()),
             crate::gen::u8::any().with_shrinker(crate::shrink::none()),
         ]);
 
         let without_shrinker = super::mix_evenly(&[
             crate::gen::u8::any().with_shrinker(crate::shrink::none()),
-            crate::gen::u8::any().with_shrinker(crate::shrink::int()),
+            crate::gen::u8::any().with_shrinker(crate::shrink::int_to_zero()),
         ]);
 
         assert_generator_can_shrink(with_shrinker, 10);

src/gen/sized.rs

@@ -46,7 +46,7 @@ pub fn progressively_increasing(
         max_iterator(start_size, percent_increase, max_size)
             .map(move |max| rng.sample(Uniform::new_inclusive(0usize, max)))
     })
-    .with_shrinker(crate::shrink::int())
+    .with_shrinker(crate::shrink::int_to_zero())
 }
 
 fn max_iterator(

src/shrink.rs

@@ -15,7 +15,12 @@ pub use bool::bool_to_true;
 pub use float::float;
 pub use from_fn::from_fn;
 pub use from_fn::from_fn_boxed;
-pub use integer::int_to_zero as int;
+
+#[allow(deprecated)]
+pub use integer::int;
+pub use integer::int_in_range;
+pub use integer::int_to_zero;
+
 pub use map::map;
 pub use no_shrink::none;
 pub use zip::zip;