Auto merge of #50274 - pietroalbini:beta-backports, r=alexcrichton

[beta] More backports

* #49368: Feature gate where clauses on associated types
* #50253: drop elaboration should reveal all *(needs `beta-accepted` stamp)*

r? @alexcrichton

Author: bors

src/librustc/traits/fulfill.rs

@@ -112,7 +112,7 @@ impl<'a, 'gcx, 'tcx> FulfillmentContext<'tcx> {
                 selcx,
                 register_region_obligations: self.register_region_obligations
             });
-            debug!("select: outcome={:?}", outcome);
+            debug!("select: outcome={:#?}", outcome);
 
             // FIXME: if we kept the original cache key, we could mark projection
             // obligations as complete for the projection cache here.

src/librustc/traits/project.rs

@@ -196,7 +196,10 @@ pub fn poly_project_and_unify_type<'cx, 'gcx, 'tcx>(
                 let span = obligation.cause.span;
                 match infcx.leak_check(false, span, &skol_map, snapshot) {
                     Ok(()) => Ok(infcx.plug_leaks(skol_map, snapshot, result)),
-                    Err(e) => Err(MismatchedProjectionTypes { err: e }),
+                    Err(e) => {
+                        debug!("poly_project_and_unify_type: leak check encountered error {:?}", e);
+                        Err(MismatchedProjectionTypes { err: e })
+                    }
                 }
             }
             Err(e) => {
@@ -243,7 +246,10 @@ fn project_and_unify_type<'cx, 'gcx, 'tcx>(
             obligations.extend(inferred_obligations);
             Ok(Some(obligations))
         },
-        Err(err) => Err(MismatchedProjectionTypes { err: err }),
+        Err(err) => {
+            debug!("project_and_unify_type: equating types encountered error {:?}", err);
+            Err(MismatchedProjectionTypes { err: err })
+        }
     }
 }
 

src/librustc_mir/shim.rs

@@ -210,7 +210,7 @@ fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     if let Some(..) = ty {
         let patch = {
-            let param_env = tcx.param_env(def_id);
+            let param_env = tcx.param_env(def_id).with_reveal_all();
             let mut elaborator = DropShimElaborator {
                 mir: &mir,
                 patch: MirPatch::new(&mir),

src/librustc_mir/transform/elaborate_drops.rs

@@ -50,7 +50,7 @@ impl MirPass for ElaborateDrops {
             (hir::BodyOwnerKind::Fn, None) => {},
             _ => return
         }
-        let param_env = tcx.param_env(src.def_id);
+        let param_env = tcx.param_env(src.def_id).with_reveal_all();
         let move_data = MoveData::gather_moves(mir, tcx).unwrap();
         let elaborate_patch = {
             let mir = &*mir;

src/librustc_mir/util/elaborate_drops.rs

@@ -13,6 +13,7 @@ use rustc::hir;
 use rustc::mir::*;
 use rustc::middle::const_val::ConstVal;
 use rustc::middle::lang_items;
+use rustc::traits::Reveal;
 use rustc::ty::{self, Ty, TyCtxt};
 use rustc::ty::subst::{Kind, Substs};
 use rustc::ty::util::IntTypeExt;
@@ -206,6 +207,7 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
             let field = Field::new(i);
             let subpath = self.elaborator.field_subpath(variant_path, field);
 
+            assert_eq!(self.elaborator.param_env().reveal, Reveal::All);
             let field_ty = self.tcx().normalize_erasing_regions(
                 self.elaborator.param_env(),
                 f.ty(self.tcx(), substs),

src/librustc_traits/normalize_erasing_regions.rs

@@ -17,6 +17,8 @@ crate fn normalize_ty_after_erasing_regions<'tcx>(
     tcx: TyCtxt<'_, 'tcx, 'tcx>,
     goal: ParamEnvAnd<'tcx, Ty<'tcx>>,
 ) -> Ty<'tcx> {
+    debug!("normalize_ty_after_erasing_regions(goal={:#?})", goal);
+
     let ParamEnvAnd { param_env, value } = goal;
     tcx.sess
         .perf_stats

src/libsyntax/feature_gate.rs

@@ -1724,8 +1724,8 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
             ast::TraitItemKind::Type(_, ref default) => {
-                // We use two if statements instead of something like match guards so that both
-                // of these errors can be emitted if both cases apply.
+                // We use three if statements instead of something like match guards so that all
+                // of these errors can be emitted if all cases apply.
                 if default.is_some() {
                     gate_feature_post!(&self, associated_type_defaults, ti.span,
                                        "associated type defaults are unstable");
@@ -1734,6 +1734,10 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     gate_feature_post!(&self, generic_associated_types, ti.span,
                                        "generic associated types are unstable");
                 }
+                if !ti.generics.where_clause.predicates.is_empty() {
+                    gate_feature_post!(&self, generic_associated_types, ti.span,
+                                       "where clauses on associated types are unstable");
+                }
             }
             _ => {}
         }

src/test/run-pass/issue-49685.rs

@@ -0,0 +1,22 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for #49685: drop elaboration was not revealing the
+// value of `impl Trait` returns, leading to an ICE.
+
+fn main() {
+    let _ = Some(())
+        .into_iter()
+        .flat_map(|_| Some(()).into_iter().flat_map(func));
+}
+
+fn func(_: ()) -> impl Iterator<Item = ()> {
+    Some(()).into_iter().flat_map(|_| vec![])
+}

src/test/ui/feature-gate-generic_associated_types.rs

@@ -15,6 +15,7 @@ trait PointerFamily<U> {
     //~^ ERROR generic associated types are unstable
     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
     //~^ ERROR generic associated types are unstable
+    //~| ERROR where clauses on associated types are unstable
 }
 
 struct Foo;
@@ -25,4 +26,10 @@ impl PointerFamily<u32> for Foo {
     //~^ ERROR generic associated types are unstable
 }
 
+trait Bar {
+    type Assoc where Self: Sized;
+    //~^ ERROR where clauses on associated types are unstable
+}
+
+
 fn main() {}

src/test/ui/feature-gate-generic_associated_types.stderr

@@ -14,22 +14,38 @@ LL |     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
+error[E0658]: where clauses on associated types are unstable (see issue #44265)
+  --> $DIR/feature-gate-generic_associated_types.rs:16:5
+   |
+LL |     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(generic_associated_types)] to the crate attributes to enable
+
 error[E0658]: generic associated types are unstable (see issue #44265)
-  --> $DIR/feature-gate-generic_associated_types.rs:22:5
+  --> $DIR/feature-gate-generic_associated_types.rs:23:5
    |
 LL |     type Pointer<usize> = Box<usize>;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
 error[E0658]: generic associated types are unstable (see issue #44265)
-  --> $DIR/feature-gate-generic_associated_types.rs:24:5
+  --> $DIR/feature-gate-generic_associated_types.rs:25:5
    |
 LL |     type Pointer2<u32> = Box<u32>;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
-error: aborting due to 4 previous errors
+error[E0658]: where clauses on associated types are unstable (see issue #44265)
+  --> $DIR/feature-gate-generic_associated_types.rs:30:5
+   |
+LL |     type Assoc where Self: Sized;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(generic_associated_types)] to the crate attributes to enable
+
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0658`.