From b928cd91da9a209327d72ed3515fb2ea16c69947 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sat, 29 May 2021 22:21:32 +0100
Subject: [PATCH] utils: Break out format_by_fmt_hex

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 src/bundles.rs | 10 +---------
 src/prelude.rs |  1 +
 src/utils.rs   | 18 ++++++++++++++++++
 3 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/src/bundles.rs b/src/bundles.rs
index 7c85d95f..48506837 100644
--- a/src/bundles.rs
+++ b/src/bundles.rs
@@ -197,15 +197,7 @@ impl BundleSavefile {
   }
 }
 
-#[throws(fmt::Error)]
-fn fmt_hex(f: &mut Formatter, buf: &[u8]) {
-  for v in buf { write!(f, "{:02x}", v)?; }
-}
-
-impl Debug for Hash {
-  #[throws(fmt::Error)]
-  fn fmt(&self, f: &mut Formatter) { fmt_hex(f, &self.0)? }
-}
+format_by_fmt_hex!{Debug, for Hash, .0}
 impl Display for Hash {
   #[throws(fmt::Error)]
   fn fmt(&self, f: &mut Formatter) {
diff --git a/src/prelude.rs b/src/prelude.rs
index 277ae898..fbb3c86b 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -119,6 +119,7 @@ pub use base_misc::*;
 pub use crate::dbgc;
 pub use crate::{deref_to_field, deref_to_field_mut};
 pub use crate::ensure_eq;
+pub use crate::format_by_fmt_hex;
 pub use crate::matches_doesnot;
 pub use crate::trace_dbg;
 pub use crate::{want, wantok, wants, want_let, want_failed_internal};
diff --git a/src/utils.rs b/src/utils.rs
index 0573f389..75500470 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -642,3 +642,21 @@ impl<I,T> IndexVec<I,T> where I: index_vec::Idx {
     self.raw.get_or_extend_with(i.index(), f)
   }
 }
+
+
+#[throws(fmt::Error)]
+pub fn fmt_hex(f: &mut Formatter, buf: &[u8]) {
+  for v in buf { write!(f, "{:02x}", v)?; }
+}
+
+#[macro_export]
+macro_rules! format_by_fmt_hex {
+  ($trait:ty, for $self:ty, . $($memb:tt)+) => {
+    impl $trait for $self {
+      #[throws(fmt::Error)]
+      fn fmt(&self, f: &mut Formatter) {
+        fmt_hex(f, &self . $($memb)+)?
+      }
+    }
+  }
+}
-- 
2.30.2