From f458187d2836ef3061d3f662d2279e10f9de77bf Mon Sep 17 00:00:00 2001
From: teor <teor@riseup.net>
Date: Wed, 7 Jul 2021 14:45:44 +1000
Subject: [PATCH 1/2] 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.
---
 zebra-chain/src/fmt.rs | 101 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 90 insertions(+), 11 deletions(-)

diff --git a/zebra-chain/src/fmt.rs b/zebra-chain/src/fmt.rs
index e0635eedd43..601ff154af5 100644
--- a/zebra-chain/src/fmt.rs
+++ b/zebra-chain/src/fmt.rs
@@ -2,20 +2,54 @@
 
 use std::{fmt, ops};
 
+#[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 the type's name.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
+pub struct TypeNameToDebug<T>(pub T);
+
+impl<T> fmt::Debug for TypeNameToDebug<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(std::any::type_name::<T>())
+    }
+}
+
+impl<T> ops::Deref for TypeNameToDebug<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+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)]
-pub struct DisplayToDebug<T>(pub T);
+#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
+pub struct DisplayToDebug<T: fmt::Display>(pub T);
 
-impl<T> fmt::Debug for DisplayToDebug<T>
-where
-    T: fmt::Display,
-{
+impl<T: fmt::Display> fmt::Debug for DisplayToDebug<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.0.fmt(f)
     }
 }
 
-impl<T> ops::Deref for DisplayToDebug<T> {
+impl<T: fmt::Display> ops::Deref for DisplayToDebug<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -23,7 +57,13 @@ impl<T> ops::Deref for DisplayToDebug<T> {
     }
 }
 
-impl<T> From<T> for DisplayToDebug<T> {
+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>;
+}

From 6d15b88a505e2d633bf8a78ba38d820b570f3344 Mon Sep 17 00:00:00 2001
From: teor <teor@riseup.net>
Date: Fri, 9 Jul 2021 12:14:45 +1000
Subject: [PATCH 2/2] Clarify how TypeNameToDebug actually works

Co-authored-by: Janito Vaqueiro Ferreira Filho <janito.vff@gmail.com>
---
 zebra-chain/src/fmt.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/zebra-chain/src/fmt.rs b/zebra-chain/src/fmt.rs
index 601ff154af5..ff3bbd09d22 100644
--- a/zebra-chain/src/fmt.rs
+++ b/zebra-chain/src/fmt.rs
@@ -7,7 +7,7 @@ use proptest::prelude::*;
 #[cfg(any(test, feature = "proptest-impl"))]
 use proptest_derive::Arbitrary;
 
-/// Wrapper to override `Debug`, redirecting it to the type's name.
+/// Wrapper to override `Debug`, redirecting it to only output the type's name.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
 pub struct TypeNameToDebug<T>(pub T);