Properly hash enums

Author: oli-obk

clippy_lints/src/consts.rs

@@ -81,6 +81,7 @@ impl Hash for Constant {
     where
         H: Hasher,
     {
+        std::mem::discriminant(self).hash(state);
         match *self {
             Constant::Str(ref s) => {
                 s.hash(state);

clippy_lints/src/utils/hir_utils.rs

@@ -389,10 +389,18 @@ impl<'a, 'tcx: 'a> SpanlessHash<'a, 'tcx> {
 
     #[allow(clippy::many_single_char_names, clippy::too_many_lines)]
     pub fn hash_expr(&mut self, e: &Expr) {
-        if let Some(e) = constant_simple(self.cx, self.tables, e) {
+        let simple_const = constant_simple(self.cx, self.tables, e);
+
+        // const hashing may result in the same hash as some unrelated node, so add a sort of
+        // discriminant depending on which path we're choosing next
+        simple_const.is_some().hash(&mut self.s);
+
+        if let Some(e) = simple_const {
             return e.hash(&mut self.s);
         }
 
+        std::mem::discriminant(&e.node).hash(&mut self.s);
+
         match e.node {
             ExprKind::AddrOf(m, ref e) => {
                 let c: fn(_, _) -> _ = ExprKind::AddrOf;