Auto merge of #57760 - dlrobertson:varargs1, r=alexreg

[rust.git] / src / librustc / traits / select.rs

diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index 4a02b0331478ffc771880a701600a34b19dc7473..e7cc9618080c2689f0196b84364dfcc4126612ec 100644 (file)
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -34,7 +34,7 @@
 use crate::mir::interpret::GlobalId;
 use crate::ty::fast_reject;
 use crate::ty::relate::TypeRelation;
-use crate::ty::subst::{Subst, Substs};
+use crate::ty::subst::{Subst, SubstsRef};
 use crate::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable};
 
 use crate::hir;
@@ -1944,7 +1944,7 @@ fn assemble_fn_pointer_candidates(
                 if let ty::FnSig {
                     unsafety: hir::Unsafety::Normal,
                     abi: Abi::Rust,
-                    variadic: false,
+                    c_variadic: false,
                     ..
                 } = self_ty.fn_sig(self.tcx()).skip_binder()
                 {
@@ -2944,7 +2944,7 @@ fn confirm_impl_candidate(
     fn vtable_impl(
         &mut self,
         impl_def_id: DefId,
-        mut substs: Normalized<'tcx, &'tcx Substs<'tcx>>,
+        mut substs: Normalized<'tcx, SubstsRef<'tcx>>,
         cause: ObligationCause<'tcx>,
         recursion_depth: usize,
         param_env: ty::ParamEnv<'tcx>,
@@ -3315,9 +3315,27 @@ fn confirm_builtin_unsize_candidate(
                     tcx.mk_existential_predicates(iter)
                 });
                 let source_trait = tcx.mk_dynamic(existential_predicates, r_b);
+
+                // Require that the traits involved in this upcast are **equal**;
+                // only the **lifetime bound** is changed.
+                //
+                // FIXME: This condition is arguably too strong -- it
+                // would suffice for the source trait to be a
+                // *subtype* of the target trait. In particular
+                // changing from something like `for<'a, 'b> Foo<'a,
+                // 'b>` to `for<'a> Foo<'a, 'a>` should be
+                // permitted. And, indeed, in the in commit
+                // 904a0bde93f0348f69914ee90b1f8b6e4e0d7cbc, this
+                // condition was loosened. However, when the leak check was added
+                // back, using subtype here actually guies the coercion code in
+                // such a way that it accepts `old-lub-glb-object.rs`. This is probably
+                // a good thing, but I've modified this to `.eq` because I want
+                // to continue rejecting that test (as we have done for quite some time)
+                // before we are firmly comfortable with what our behavior
+                // should be there. -nikomatsakis
                 let InferOk { obligations, .. } = self.infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .sup(target, source_trait)
+                    .eq(target, source_trait) // FIXME -- see below
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
 
@@ -3520,7 +3538,7 @@ fn rematch_impl(
         impl_def_id: DefId,
         obligation: &TraitObligation<'tcx>,
         snapshot: &CombinedSnapshot<'_, 'tcx>,
-    ) -> Normalized<'tcx, &'tcx Substs<'tcx>> {
+    ) -> Normalized<'tcx, SubstsRef<'tcx>> {
         match self.match_impl(impl_def_id, obligation, snapshot) {
             Ok(substs) => substs,
             Err(()) => {
@@ -3538,7 +3556,7 @@ fn match_impl(
         impl_def_id: DefId,
         obligation: &TraitObligation<'tcx>,
         snapshot: &CombinedSnapshot<'_, 'tcx>,
-    ) -> Result<Normalized<'tcx, &'tcx Substs<'tcx>>, ()> {
+    ) -> Result<Normalized<'tcx, SubstsRef<'tcx>>, ()> {
         let impl_trait_ref = self.tcx().impl_trait_ref(impl_def_id).unwrap();
 
         // Before we create the substitutions and everything, first
@@ -3743,7 +3761,7 @@ fn impl_or_trait_obligations(
         recursion_depth: usize,
         param_env: ty::ParamEnv<'tcx>,
         def_id: DefId,         // of impl or trait
-        substs: &Substs<'tcx>, // for impl or trait
+        substs: SubstsRef<'tcx>,  // for impl or trait
     ) -> Vec<PredicateObligation<'tcx>> {
         debug!("impl_or_trait_obligations(def_id={:?})", def_id);
         let tcx = self.tcx();