1 files changed, 26 insertions, 1 deletions
diff --git a/compiler/rustc_metadata/src/rmeta/table.rs b/compiler/rustc_metadata/src/rmeta/table.rs
index b89d48ec1..364fa74ab 100644
--- a/compiler/rustc_metadata/src/rmeta/table.rs
+++ b/compiler/rustc_metadata/src/rmeta/table.rs
@@ -3,7 +3,7 @@ use crate::rmeta::*;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_hir::def::{CtorKind, CtorOf};
 use rustc_index::vec::Idx;
-use rustc_middle::ty::ParameterizedOverTcx;
+use rustc_middle::ty::{ParameterizedOverTcx, UnusedGenericParams};
 use rustc_serialize::opaque::FileEncoder;
 use rustc_serialize::Encoder as _;
 use rustc_span::hygiene::MacroKind;
@@ -50,6 +50,16 @@ impl IsDefault for DefPathHash {
     }
 }
 
+impl IsDefault for UnusedGenericParams {
+    fn is_default(&self) -> bool {
+        // UnusedGenericParams encodes the *un*usedness as a bitset.
+        // This means that 0 corresponds to all bits used, which is indeed the default.
+        let is_default = self.bits() == 0;
+        debug_assert_eq!(is_default, self.all_used());
+        is_default
+    }
+}
+
 /// Helper trait, for encoding to, and decoding from, a fixed number of bytes.
 /// Used mainly for Lazy positions and lengths.
 /// Unchecked invariant: `Self::default()` should encode as `[0; BYTE_LEN]`,
@@ -271,6 +281,21 @@ impl FixedSizeEncoding for bool {
     }
 }
 
+impl FixedSizeEncoding for UnusedGenericParams {
+    type ByteArray = [u8; 4];
+
+    #[inline]
+    fn from_bytes(b: &[u8; 4]) -> Self {
+        let x: u32 = u32::from_bytes(b);
+        UnusedGenericParams::from_bits(x)
+    }
+
+    #[inline]
+    fn write_to_bytes(self, b: &mut [u8; 4]) {
+        self.bits().write_to_bytes(b);
+    }
+}
+
 // NOTE(eddyb) there could be an impl for `usize`, which would enable a more
 // generic `LazyValue<T>` impl, but in the general case we might not need / want
 // to fit every `usize` in `u32`.