Auto merge of #70994 - Centril:rollup-lftv0a3, r=Centril

Rollup of 9 pull requests

Successful merges:

 - #69745 (Use `PredicateObligation`s instead of `Predicate`s)
 - #70938 (Add ThreadSanitizer test case)
 - #70973 (Use forward traversal for unconditional recursion lint)
 - #70978 (compiletest: let config flags overwrite -A unused)
 - #70979 (Follow up on BTreeMap comments)
 - #70981 (Rearrange BTreeMap::into_iter to match range_mut.)
 - #70985 (Clean up E0512 explanation)
 - #70988 (Setup the `@rustbot prioritize` command)
 - #70991 (fix rustc-dev-guide's url in src/librustc_codegen_ssa)

Failed merges:

r? @ghost

src/liballoc/collections/btree/map.rs

@@ -1544,19 +1544,19 @@ impl<K, V> IntoIterator for BTreeMap<K, V> {
     type IntoIter = IntoIter<K, V>;
 
     fn into_iter(self) -> IntoIter<K, V> {
-        let me = ManuallyDrop::new(self);
-        if me.root.is_none() {
-            return IntoIter { front: None, back: None, length: 0 };
-        }
-
-        let root1 = unsafe { unwrap_unchecked(ptr::read(&me.root)).into_ref() };
-        let root2 = unsafe { unwrap_unchecked(ptr::read(&me.root)).into_ref() };
-        let len = me.length;
-
-        IntoIter {
-            front: Some(root1.first_leaf_edge()),
-            back: Some(root2.last_leaf_edge()),
-            length: len,
+        let mut me = ManuallyDrop::new(self);
+        if let Some(root) = me.root.as_mut() {
+            let root1 = unsafe { ptr::read(root).into_ref() };
+            let root2 = unsafe { ptr::read(root).into_ref() };
+            let len = me.length;
+
+            IntoIter {
+                front: Some(root1.first_leaf_edge()),
+                back: Some(root2.last_leaf_edge()),
+                length: len,
+            }
+        } else {
+            IntoIter { front: None, back: None, length: 0 }
         }
     }
 }
@@ -2771,8 +2771,6 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInter
                             pos.next_unchecked();
                         }
                     }
-
-                    // This internal node might be underfull, but only if it's the root.
                     break;
                 }
             }

src/liballoc/collections/btree/node.rs

@@ -161,7 +161,7 @@ impl<K, V> Root<K, V> {
         NodeRef {
             height: self.height,
             node: self.node.as_ptr(),
-            root: self as *const _ as *mut _,
+            root: ptr::null(),
             _marker: PhantomData,
         }
     }
@@ -179,7 +179,7 @@ impl<K, V> Root<K, V> {
         NodeRef {
             height: self.height,
             node: self.node.as_ptr(),
-            root: ptr::null_mut(), // FIXME: Is there anything better to do here?
+            root: ptr::null(),
             _marker: PhantomData,
         }
     }

src/librustc_codegen_ssa/README.md

@@ -1,3 +1,3 @@
 Please read the rustc-dev-guide chapter on [Backend Agnostic Codegen][bac].
 
-[bac]: https://rustc-dev-guide.rust-lang.org/codegen/backend-agnostic.html
+[bac]: https://rustc-dev-guide.rust-lang.org/backend/backend-agnostic.html

src/librustc_data_structures/graph/iterate/mod.rs

@@ -209,7 +209,9 @@ where
                     // schedule its successors for examination.
                     self.stack.push(Event { node, becomes: Settled });
                     for succ in self.graph.successors(node) {
-                        self.stack.push(Event { node: succ, becomes: Visited });
+                        if !visitor.ignore_edge(node, succ) {
+                            self.stack.push(Event { node: succ, becomes: Visited });
+                        }
                     }
                 }
             }
@@ -255,16 +257,21 @@ where
     /// [CLR]: https://en.wikipedia.org/wiki/Introduction_to_Algorithms
     fn node_examined(
         &mut self,
-        _target: G::Node,
+        _node: G::Node,
         _prior_status: Option<NodeStatus>,
     ) -> ControlFlow<Self::BreakVal> {
         ControlFlow::Continue
     }
 
     /// Called after all nodes reachable from this one have been examined.
-    fn node_settled(&mut self, _target: G::Node) -> ControlFlow<Self::BreakVal> {
+    fn node_settled(&mut self, _node: G::Node) -> ControlFlow<Self::BreakVal> {
         ControlFlow::Continue
     }
+
+    /// Behave as if no edges exist from `source` to `target`.
+    fn ignore_edge(&mut self, _source: G::Node, _target: G::Node) -> bool {
+        false
+    }
 }
 
 /// This `TriColorVisitor` looks for back edges in a graph, which indicate that a cycle exists.

src/librustc_error_codes/error_codes/E0512.md

@@ -1,5 +1,6 @@
-Transmute with two differently sized types was attempted. Erroneous code
-example:
+Transmute with two differently sized types was attempted.
+
+Erroneous code example:
 
 ```compile_fail,E0512
 fn takes_u8(_: u8) {}

src/librustc_infer/infer/outlives/verify.rs

@@ -296,7 +296,10 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         let identity_proj = tcx.mk_projection(assoc_item_def_id, identity_substs);
         self.collect_outlives_from_predicate_list(
             move |ty| ty == identity_proj,
-            traits::elaborate_predicates(tcx, trait_predicates),
+            traits::elaborate_predicates(tcx, trait_predicates)
+                .into_iter()
+                .map(|o| o.predicate)
+                .collect::<Vec<_>>(),
         )
         .map(|b| b.1)
     }

src/librustc_infer/traits/util.rs

@@ -1,8 +1,10 @@
 use smallvec::smallvec;
 
+use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::ty::outlives::Component;
 use rustc_middle::ty::{self, ToPolyTraitRef, ToPredicate, TyCtxt, WithConstness};
+use rustc_span::Span;
 
 pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -87,7 +89,7 @@ impl<T: AsRef<ty::Predicate<'tcx>>> Extend<T> for PredicateSet<'tcx> {
 /// holds as well. Similarly, if we have `trait Foo: 'static`, and we know that
 /// `T: Foo`, then we know that `T: 'static`.
 pub struct Elaborator<'tcx> {
-    stack: Vec<ty::Predicate<'tcx>>,
+    stack: Vec<PredicateObligation<'tcx>>,
     visited: PredicateSet<'tcx>,
 }
 
@@ -112,35 +114,60 @@ pub fn elaborate_predicates<'tcx>(
 ) -> Elaborator<'tcx> {
     let mut visited = PredicateSet::new(tcx);
     predicates.retain(|pred| visited.insert(pred));
-    Elaborator { stack: predicates, visited }
+    let obligations: Vec<_> =
+        predicates.into_iter().map(|predicate| predicate_obligation(predicate, None)).collect();
+    elaborate_obligations(tcx, obligations)
+}
+
+pub fn elaborate_obligations<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    mut obligations: Vec<PredicateObligation<'tcx>>,
+) -> Elaborator<'tcx> {
+    let mut visited = PredicateSet::new(tcx);
+    obligations.retain(|obligation| visited.insert(&obligation.predicate));
+    Elaborator { stack: obligations, visited }
+}
+
+fn predicate_obligation<'tcx>(
+    predicate: ty::Predicate<'tcx>,
+    span: Option<Span>,
+) -> PredicateObligation<'tcx> {
+    let mut cause = ObligationCause::dummy();
+    if let Some(span) = span {
+        cause.span = span;
+    }
+    Obligation { cause, param_env: ty::ParamEnv::empty(), recursion_depth: 0, predicate }
 }
 
 impl Elaborator<'tcx> {
     pub fn filter_to_traits(self) -> FilterToTraits<Self> {
         FilterToTraits::new(self)
     }
 
-    fn elaborate(&mut self, predicate: &ty::Predicate<'tcx>) {
+    fn elaborate(&mut self, obligation: &PredicateObligation<'tcx>) {
         let tcx = self.visited.tcx;
-        match *predicate {
+        match obligation.predicate {
             ty::Predicate::Trait(ref data, _) => {
                 // Get predicates declared on the trait.
                 let predicates = tcx.super_predicates_of(data.def_id());
 
-                let predicates = predicates
-                    .predicates
-                    .iter()
-                    .map(|(pred, _)| pred.subst_supertrait(tcx, &data.to_poly_trait_ref()));
-                debug!("super_predicates: data={:?} predicates={:?}", data, predicates.clone());
+                let obligations = predicates.predicates.iter().map(|(pred, span)| {
+                    predicate_obligation(
+                        pred.subst_supertrait(tcx, &data.to_poly_trait_ref()),
+                        Some(*span),
+                    )
+                });
+                debug!("super_predicates: data={:?} predicates={:?}", data, &obligations);
 
                 // Only keep those bounds that we haven't already seen.
                 // This is necessary to prevent infinite recursion in some
                 // cases. One common case is when people define
                 // `trait Sized: Sized { }` rather than `trait Sized { }`.
                 let visited = &mut self.visited;
-                let predicates = predicates.filter(|pred| visited.insert(pred));
+                let obligations =
+                    obligations.filter(|obligation| visited.insert(&obligation.predicate));
 
-                self.stack.extend(predicates);
+                self.stack.extend(obligations);
             }
             ty::Predicate::WellFormed(..) => {
                 // Currently, we do not elaborate WF predicates,
@@ -221,25 +248,26 @@ impl Elaborator<'tcx> {
                                 None
                             }
                         })
-                        .filter(|p| visited.insert(p)),
+                        .filter(|p| visited.insert(p))
+                        .map(|p| predicate_obligation(p, None)),
                 );
             }
         }
     }
 }
 
 impl Iterator for Elaborator<'tcx> {
-    type Item = ty::Predicate<'tcx>;
+    type Item = PredicateObligation<'tcx>;
 
     fn size_hint(&self) -> (usize, Option<usize>) {
         (self.stack.len(), None)
     }
 
-    fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
+    fn next(&mut self) -> Option<Self::Item> {
         // Extract next item from top-most stack frame, if any.
-        if let Some(pred) = self.stack.pop() {
-            self.elaborate(&pred);
-            Some(pred)
+        if let Some(obligation) = self.stack.pop() {
+            self.elaborate(&obligation);
+            Some(obligation)
         } else {
             None
         }
@@ -282,12 +310,12 @@ impl<I> FilterToTraits<I> {
     }
 }
 
-impl<'tcx, I: Iterator<Item = ty::Predicate<'tcx>>> Iterator for FilterToTraits<I> {
+impl<'tcx, I: Iterator<Item = PredicateObligation<'tcx>>> Iterator for FilterToTraits<I> {
     type Item = ty::PolyTraitRef<'tcx>;
 
     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
-        while let Some(pred) = self.base_iterator.next() {
-            if let ty::Predicate::Trait(data, _) = pred {
+        while let Some(obligation) = self.base_iterator.next() {
+            if let ty::Predicate::Trait(data, _) = obligation.predicate {
                 return Some(data.to_poly_trait_ref());
             }
         }

src/librustc_mir/transform/const_prop.rs

@@ -126,7 +126,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
             .collect();
         if !traits::normalize_and_test_predicates(
             tcx,
-            traits::elaborate_predicates(tcx, predicates).collect(),
+            traits::elaborate_predicates(tcx, predicates).map(|o| o.predicate).collect(),
         ) {
             trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", source.def_id());
             return;

src/librustc_mir_build/build/mod.rs

@@ -178,11 +178,11 @@ fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> BodyAndCache<'_> {
             build::construct_const(cx, body_id, return_ty, return_ty_span)
         };
 
+        lints::check(tcx, &body, def_id);
+
         let mut body = BodyAndCache::new(body);
         body.ensure_predecessors();
 
-        lints::check(tcx, &body.unwrap_read_only(), def_id);
-
         // The borrow checker will replace all the regions here with its own
         // inference variables. There's no point having non-erased regions here.
         // The exception is `body.user_type_annotations`, which is used unmodified