Improve debug formatting for primary/secondary map (#11081)

* Improve debug formatting for primary/secondary map

* clippy suggestion

* review suggestions

Author: simvux

cranelift/entity/src/map.rs

@@ -5,6 +5,7 @@ use crate::iter::{Iter, IterMut};
 use crate::keys::Keys;
 use alloc::vec::Vec;
 use core::cmp::min;
+use core::fmt;
 use core::marker::PhantomData;
 use core::ops::{Index, IndexMut};
 use core::slice;
@@ -23,7 +24,7 @@ use serde::{
 ///
 /// The map does not track if an entry for a key has been inserted or not. Instead it behaves as if
 /// all keys have a default entry from the beginning.
-#[derive(Debug, Clone, Hash)]
+#[derive(Clone, Hash)]
 pub struct SecondaryMap<K, V>
 where
     K: EntityRef,
@@ -282,6 +283,15 @@ where
     }
 }
 
+impl<K: EntityRef + fmt::Debug, V: fmt::Debug + Clone> fmt::Debug for SecondaryMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SecondaryMap")
+            .field("elems", &self.elems)
+            .field("default", &self.default)
+            .finish()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

cranelift/entity/src/primary.rs

@@ -5,6 +5,7 @@ use crate::iter::{IntoIter, Iter, IterMut};
 use crate::keys::Keys;
 use alloc::boxed::Box;
 use alloc::vec::Vec;
+use core::fmt;
 use core::marker::PhantomData;
 use core::mem;
 use core::ops::{Index, IndexMut};
@@ -27,7 +28,7 @@ use serde_derive::{Deserialize, Serialize};
 /// that it only allows indexing with the distinct `EntityRef` key type, so converting to a
 /// plain slice would make it easier to use incorrectly. To make a slice of a `PrimaryMap`, use
 /// `into_boxed_slice`.
-#[derive(Debug, Clone, Hash, PartialEq, Eq)]
+#[derive(Clone, Hash, PartialEq, Eq)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
 pub struct PrimaryMap<K, V>
 where
@@ -336,6 +337,16 @@ where
     }
 }
 
+impl<K: EntityRef + fmt::Debug, V: fmt::Debug> fmt::Debug for PrimaryMap<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut struct_ = f.debug_struct("PrimaryMap");
+        for (k, v) in self {
+            struct_.field(&alloc::format!("{k:?}"), v);
+        }
+        struct_.finish()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;