Auto merge of #18977 - Manishearth:map-len, r=Gankro

Include map length in diagnostics

If this doesn't match with the size it's more likely for anything caught
t be hardware corruption. If it does the situation is more interesting.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/18977)
<!-- Reviewable:end -->

components/hashglobe/src/diagnostic.rs

@@ -62,17 +62,21 @@ impl<K: Hash + Eq, V, S: BuildHasher> DiagnosticHashMap<K, V, S>
         let mut position = 0;
         let mut count = 0;
         let mut bad_canary = None;
-        for (_,v) in self.map.iter() {
+
+        let mut iter = self.map.iter();
+        while let Some((h, _, v)) = iter.next_with_hash() {
             let canary_ref = &v.0;
             position += 1;
+
             if *canary_ref == CANARY {
                 continue;
             }
+
             count += 1;
-            bad_canary = Some((*canary_ref, canary_ref, position));
+            bad_canary = Some((h, *canary_ref, canary_ref, position));
         }
         if let Some(c) = bad_canary {
-            self.report_corruption(c.0, c.1, c.2, count);
+            self.report_corruption(c.0, c.1, c.2, c.3, count);
         }
     }
 
@@ -158,10 +162,11 @@ impl<K: Hash + Eq, V, S: BuildHasher> DiagnosticHashMap<K, V, S>
     #[inline(never)]
     fn report_corruption(
         &self,
+        hash: usize,
         canary: usize,
         canary_addr: *const usize,
         position: usize,
-        count: usize,
+        count: usize
     ) {
         use ::std::ffi::CString;
         let key = b"HashMapJournal\0";
@@ -172,12 +177,15 @@ impl<K: Hash + Eq, V, S: BuildHasher> DiagnosticHashMap<K, V, S>
                 value.as_ptr(),
             );
         }
+
         panic!(
-            concat!("HashMap Corruption (sz={}, cap={}, pairsz={}, cnry={:#x}, count={}, ",
-                    "last_pos={}, base_addr={:?}, cnry_addr={:?}, jrnl_len={})"),
+            concat!("HashMap Corruption (sz={}, buffer_hash_sz={}, cap={}, pairsz={}, hash={:#x}, cnry={:#x}, ",
+                "count={}, last_pos={}, base_addr={:?}, cnry_addr={:?}, jrnl_len={})"),
             self.map.len(),
+            self.map.diagnostic_count_hashes(),
             self.map.raw_capacity(),
             ::std::mem::size_of::<(K, (usize, V))>(),
+            hash,
             canary,
             count,
             position,

components/hashglobe/src/hash_map.rs

@@ -1257,6 +1257,10 @@ impl<K, V, S> HashMap<K, V, S>
             debug_assert!(elems_left == 0 || bucket.index() != start_index);
         }
     }
+
+    pub fn diagnostic_count_hashes(&self) -> usize {
+        self.table.diagnostic_count_hashes()
+    }
 }
 
 impl<K, V, S> PartialEq for HashMap<K, V, S>
@@ -1339,6 +1343,12 @@ impl<'a, K: Debug, V: Debug> fmt::Debug for Iter<'a, K, V> {
     }
 }
 
+impl<'a, K: 'a, V: 'a>  Iter<'a, K, V> {
+    pub fn next_with_hash(&mut self) -> Option<(usize, &'a K, &'a V)> {
+        self.inner.next_with_hash()
+    }
+}
+
 /// A mutable iterator over the entries of a `HashMap`.
 ///
 /// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its

components/hashglobe/src/table.rs

@@ -896,6 +896,10 @@ impl<K, V> RawTable<K, V> {
         }
     }
 
+    pub fn diagnostic_count_hashes(&self) -> usize {
+        (0..self.capacity()).filter(|&i| unsafe { *self.raw_bucket_at(i).hash() != EMPTY_BUCKET }).count()
+    }
+
     pub fn iter(&self) -> Iter<K, V> {
         Iter {
             iter: self.raw_buckets(),
@@ -1130,6 +1134,15 @@ impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
     }
 }
 
+impl<'a, K, V> Iter<'a, K, V> {
+    pub fn next_with_hash(&mut self) -> Option<(usize, &'a K, &'a V)> {
+        self.iter.next().map(|raw| unsafe {
+            let (hash_ptr, pair_ptr) = raw.hash_pair();
+            (*hash_ptr, &(*pair_ptr).0, &(*pair_ptr).1)
+        })
+    }
+}
+
 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
     type Item = (&'a K, &'a mut V);