Add a TypeNameToDebug formatter to zebra_chain (#2466)

* Add a TypeNameToDebug formatter to zebra_chain

This formatter makes it much easier to diagnose proptest errors.
It will be used in a future PR.

Implement Arbitrary and DerefMut for all the formatters.

Also make the formatter type bounds consistent,
to produce better compiler errors.

* Clarify how TypeNameToDebug actually works

Co-authored-by: Janito Vaqueiro Ferreira Filho <janito.vff@gmail.com>

Co-authored-by: Janito Vaqueiro Ferreira Filho <janito.vff@gmail.com>

zebra-chain/src/fmt.rs

@@ -2,20 +2,23 @@
 
 use std::{fmt, ops};
 
-/// Wrapper to override `Debug`, redirecting it to the `Display` impl.
+#[cfg(any(test, feature = "proptest-impl"))]
+use proptest::prelude::*;
+#[cfg(any(test, feature = "proptest-impl"))]
+use proptest_derive::Arbitrary;
+
+/// Wrapper to override `Debug`, redirecting it to only output the type's name.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct DisplayToDebug<T>(pub T);
+#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
+pub struct TypeNameToDebug<T>(pub T);
 
-impl<T> fmt::Debug for DisplayToDebug<T>
+impl<T> fmt::Debug for TypeNameToDebug<T> {
-where
-    T: fmt::Display,
-{
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.0.fmt(f)
+        f.write_str(std::any::type_name::<T>())
     }
 }
 
-impl<T> ops::Deref for DisplayToDebug<T> {
+impl<T> ops::Deref for TypeNameToDebug<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -23,7 +26,44 @@ impl<T> ops::Deref for DisplayToDebug<T> {
     }
 }
 
-impl<T> From<T> for DisplayToDebug<T> {
+impl<T> ops::DerefMut for TypeNameToDebug<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<T> From<T> for TypeNameToDebug<T> {
+    fn from(t: T) -> Self {
+        Self(t)
+    }
+}
+
+/// Wrapper to override `Debug`, redirecting it to the `Display` impl.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
+pub struct DisplayToDebug<T: fmt::Display>(pub T);
+
+impl<T: fmt::Display> fmt::Debug for DisplayToDebug<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl<T: fmt::Display> ops::Deref for DisplayToDebug<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T: fmt::Display> ops::DerefMut for DisplayToDebug<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<T: fmt::Display> From<T> for DisplayToDebug<T> {
     fn from(t: T) -> Self {
         Self(t)
     }
@@ -34,7 +74,10 @@ impl<T> From<T> for DisplayToDebug<T> {
 /// For collections and exact size iterators, it only displays the
 /// collection/iterator type, the item type, and the length.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct SummaryDebug<CollectionOrIter>(pub CollectionOrIter);
+pub struct SummaryDebug<CollectionOrIter>(pub CollectionOrIter)
+where
+    CollectionOrIter: IntoIterator + Clone,
+    <CollectionOrIter as IntoIterator>::IntoIter: ExactSizeIterator;
 
 impl<CollectionOrIter> fmt::Debug for SummaryDebug<CollectionOrIter>
 where
@@ -52,7 +95,11 @@ where
     }
 }
 
-impl<CollectionOrIter> ops::Deref for SummaryDebug<CollectionOrIter> {
+impl<CollectionOrIter> ops::Deref for SummaryDebug<CollectionOrIter>
+where
+    CollectionOrIter: IntoIterator + Clone,
+    <CollectionOrIter as IntoIterator>::IntoIter: ExactSizeIterator,
+{
     type Target = CollectionOrIter;
 
     fn deref(&self) -> &Self::Target {
@@ -60,7 +107,21 @@ impl<CollectionOrIter> ops::Deref for SummaryDebug<CollectionOrIter> {
     }
 }
 
-impl<CollectionOrIter> From<CollectionOrIter> for SummaryDebug<CollectionOrIter> {
+impl<CollectionOrIter> ops::DerefMut for SummaryDebug<CollectionOrIter>
+where
+    CollectionOrIter: IntoIterator + Clone,
+    <CollectionOrIter as IntoIterator>::IntoIter: ExactSizeIterator,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<CollectionOrIter> From<CollectionOrIter> for SummaryDebug<CollectionOrIter>
+where
+    CollectionOrIter: IntoIterator + Clone,
+    <CollectionOrIter as IntoIterator>::IntoIter: ExactSizeIterator,
+{
     fn from(collection: CollectionOrIter) -> Self {
         Self(collection)
     }
@@ -68,7 +129,8 @@ impl<CollectionOrIter> From<CollectionOrIter> for SummaryDebug<CollectionOrIter>
 
 impl<CollectionOrIter> IntoIterator for SummaryDebug<CollectionOrIter>
 where
-    CollectionOrIter: IntoIterator,
+    CollectionOrIter: IntoIterator + Clone,
+    <CollectionOrIter as IntoIterator>::IntoIter: ExactSizeIterator,
 {
     type Item = <CollectionOrIter as IntoIterator>::Item;
     type IntoIter = <CollectionOrIter as IntoIterator>::IntoIter;
@@ -77,3 +139,20 @@ where
         self.0.into_iter()
     }
 }
+
+#[cfg(any(test, feature = "proptest-impl"))]
+impl<CollectionOrIter> Arbitrary for SummaryDebug<CollectionOrIter>
+where
+    CollectionOrIter: Arbitrary + IntoIterator + Clone + 'static,
+    <CollectionOrIter as IntoIterator>::IntoIter: ExactSizeIterator,
+{
+    type Parameters = <CollectionOrIter as Arbitrary>::Parameters;
+
+    fn arbitrary_with(args: Self::Parameters) -> Self::Strategy {
+        CollectionOrIter::arbitrary_with(args)
+            .prop_map_into()
+            .boxed()
+    }
+
+    type Strategy = BoxedStrategy<Self>;
+}