Auto merge of #27641 - nikomatsakis:soundness-rfc-1214, r=nrc

This PR implements the majority of RFC 1214. In particular, it implements:

- the new outlives relation
- comprehensive WF checking

For the most part, new code receives warnings, not errors, though 3 regressions were found via a crater run. 

There are some deviations from RFC 1214. Most notably:

- we still consider implied bounds from fn ret; this intersects other soundness issues that I intend to address in detail in a follow-up RFC. Fixing this without breaking a lot of code probably requires rewriting compare-method somewhat (which is probably a good thing).
- object types do not check trait bounds for fear of encountering `Self`; this was left as an unresolved question in RFC 1214, but ultimately feels inconsistent.

Both of those two issues are highlighted in the tracking issue, #27579. #27579 also includes a testing matrix with new tests that I wrote -- these probably duplicate some existing tests, I tried to check but wasn't quite sure what to look for. I tried to be thorough in testing the WF relation, at least, but would welcome suggestions for missing tests.

r? @nrc (or perhaps someone else?)

src/libcore/iter.rs

@@ -2135,7 +2135,7 @@ impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
 /// two `Step` objects.
 #[unstable(feature = "step_trait",
            reason = "likely to be replaced by finer-grained traits")]
-pub trait Step: PartialOrd {
+pub trait Step: PartialOrd+Sized {
     /// Steps `self` if possible.
     fn step(&self, by: &Self) -> Option<Self>;
 

src/libcore/marker.rs

@@ -56,7 +56,7 @@ pub trait Sized {
 /// Types that can be "unsized" to a dynamically sized type.
 #[unstable(feature = "unsize")]
 #[lang="unsize"]
-pub trait Unsize<T> {
+pub trait Unsize<T: ?Sized> {
     // Empty.
 }
 

src/libcore/num/mod.rs

@@ -19,7 +19,7 @@ use char::CharExt;
 use cmp::{Eq, PartialOrd};
 use fmt;
 use intrinsics;
-use marker::Copy;
+use marker::{Copy, Sized};
 use mem::size_of;
 use option::Option::{self, Some, None};
 use result::Result::{self, Ok, Err};
@@ -1263,7 +1263,7 @@ pub enum FpCategory {
 #[doc(hidden)]
 #[unstable(feature = "core_float",
            reason = "stable interface is via `impl f{32,64}` in later crates")]
-pub trait Float {
+pub trait Float: Sized {
     /// Returns the NaN value.
     fn nan() -> Self;
     /// Returns the infinite value.

src/libcore/str/mod.rs

@@ -25,6 +25,7 @@ use default::Default;
 use fmt;
 use iter::ExactSizeIterator;
 use iter::{Map, Iterator, DoubleEndedIterator};
+use marker::Sized;
 use mem;
 use ops::{Fn, FnMut, FnOnce};
 use option::Option::{self, None, Some};
@@ -37,7 +38,7 @@ pub mod pattern;
 /// A trait to abstract the idea of creating a new instance of a type from a
 /// string.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait FromStr {
+pub trait FromStr: Sized {
     /// The associated error which can be returned from parsing.
     #[stable(feature = "rust1", since = "1.0.0")]
     type Err;

src/libgraphviz/lib.rs

@@ -561,7 +561,7 @@ pub type Edges<'a,E> = Cow<'a,[E]>;
 /// `Cow<[T]>` to leave implementers the freedom to create
 /// entirely new vectors or to pass back slices into internally owned
 /// vectors.
-pub trait GraphWalk<'a, N, E> {
+pub trait GraphWalk<'a, N: Clone, E: Clone> {
     /// Returns all the nodes in this graph.
     fn nodes(&'a self) -> Nodes<'a, N>;
     /// Returns all of the edges in this graph.

src/librand/distributions/range.rs

@@ -12,6 +12,7 @@
 
 // this is surprisingly complicated to be both generic & correct
 
+use core::marker::Sized;
 use Rng;
 use distributions::{Sample, IndependentSample};
 
@@ -57,7 +58,7 @@ impl<Sup: SampleRange> IndependentSample<Sup> for Range<Sup> {
 /// uniformly between two values. This should not be used directly,
 /// and is only to facilitate `Range`.
 #[doc(hidden)]
-pub trait SampleRange {
+pub trait SampleRange: Sized {
     /// Construct the `Range` object that `sample_range`
     /// requires. This should not ever be called directly, only via
     /// `Range::new`, which will check that `low < high`, so this

src/librustc/lib.rs

@@ -129,6 +129,7 @@ pub mod middle {
     pub mod lang_items;
     pub mod liveness;
     pub mod mem_categorization;
+    pub mod outlives;
     pub mod pat_util;
     pub mod privacy;
     pub mod reachable;
@@ -143,6 +144,7 @@ pub mod middle {
     pub mod ty_match;
     pub mod ty_relate;
     pub mod ty_walk;
+    pub mod wf;
     pub mod weak_lang_items;
 }
 

src/librustc/metadata/tydecode.rs

@@ -790,6 +790,12 @@ fn parse_predicate_<'a,'tcx, F>(st: &mut PState<'a, 'tcx>,
         'o' => ty::Binder(ty::OutlivesPredicate(parse_ty_(st, conv),
                                                 parse_region_(st, conv))).to_predicate(),
         'p' => ty::Binder(parse_projection_predicate_(st, conv)).to_predicate(),
+        'w' => ty::Predicate::WellFormed(parse_ty_(st, conv)),
+        'O' => {
+            let def_id = parse_def_(st, NominalType, conv);
+            assert_eq!(next(st), '|');
+            ty::Predicate::ObjectSafe(def_id)
+        }
         c => panic!("Encountered invalid character in metadata: {}", c)
     }
 }

src/librustc/metadata/tyencode.rs

@@ -457,6 +457,13 @@ pub fn enc_predicate<'a, 'tcx>(w: &mut Encoder,
             mywrite!(w, "p");
             enc_projection_predicate(w, cx, data)
         }
+        ty::Predicate::WellFormed(data) => {
+            mywrite!(w, "w");
+            enc_ty(w, cx, data);
+        }
+        ty::Predicate::ObjectSafe(trait_def_id) => {
+            mywrite!(w, "O{}|", (cx.ds)(trait_def_id));
+        }
     }
 }
 

src/librustc/middle/astencode.rs

@@ -1061,7 +1061,7 @@ fn encode_side_tables_for_id(ecx: &e::EncodeContext,
     }
 }
 
-trait doc_decoder_helpers {
+trait doc_decoder_helpers: Sized {
     fn as_int(&self) -> isize;
     fn opt_child(&self, tag: c::astencode_tag) -> Option<Self>;
 }

src/librustc/middle/expr_use_visitor.rs

@@ -239,7 +239,7 @@ impl OverloadedCallType {
 // supplies types from the tree. After type checking is complete, you
 // can just use the tcx as the typer.
 
-pub struct ExprUseVisitor<'d,'t,'a: 't, 'tcx:'a> {
+pub struct ExprUseVisitor<'d, 't, 'a: 't, 'tcx:'a+'d> {
     typer: &'t infer::InferCtxt<'a, 'tcx>,
     mc: mc::MemCategorizationContext<'t, 'a, 'tcx>,
     delegate: &'d mut (Delegate<'tcx>+'d),
@@ -273,7 +273,8 @@ enum PassArgs {
 impl<'d,'t,'a,'tcx> ExprUseVisitor<'d,'t,'a,'tcx> {
     pub fn new(delegate: &'d mut Delegate<'tcx>,
                typer: &'t infer::InferCtxt<'a, 'tcx>)
-               -> ExprUseVisitor<'d,'t,'a, 'tcx> {
+               -> ExprUseVisitor<'d,'t,'a,'tcx>
+    {
         ExprUseVisitor {
             typer: typer,
             mc: mc::MemCategorizationContext::new(typer),

src/librustc/middle/free_region.rs

@@ -10,7 +10,7 @@
 
 //! This file defines
 
-use middle::implicator::Implication;
+use middle::wf::ImpliedBound;
 use middle::ty::{self, FreeRegion};
 use util::common::can_reach;
 use util::nodemap::{FnvHashMap, FnvHashSet};
@@ -30,18 +30,19 @@ impl FreeRegionMap {
         FreeRegionMap { map: FnvHashMap(), statics: FnvHashSet() }
     }
 
-    pub fn relate_free_regions_from_implications<'tcx>(&mut self,
-                                                       implications: &[Implication<'tcx>])
+    pub fn relate_free_regions_from_implied_bounds<'tcx>(&mut self,
+                                                        implied_bounds: &[ImpliedBound<'tcx>])
     {
-        for implication in implications {
-            debug!("implication: {:?}", implication);
-            match *implication {
-                Implication::RegionSubRegion(_, ty::ReFree(free_a), ty::ReFree(free_b)) => {
+        debug!("relate_free_regions_from_implied_bounds()");
+        for implied_bound in implied_bounds {
+            debug!("implied bound: {:?}", implied_bound);
+            match *implied_bound {
+                ImpliedBound::RegionSubRegion(ty::ReFree(free_a), ty::ReFree(free_b)) => {
                     self.relate_free_regions(free_a, free_b);
                 }
-                Implication::RegionSubRegion(..) |
-                Implication::RegionSubGeneric(..) |
-                Implication::Predicate(..) => {
+                ImpliedBound::RegionSubRegion(..) |
+                ImpliedBound::RegionSubParam(..) |
+                ImpliedBound::RegionSubProjection(..) => {
                 }
             }
         }
@@ -56,6 +57,8 @@ impl FreeRegionMap {
                 ty::Predicate::Projection(..) |
                 ty::Predicate::Trait(..) |
                 ty::Predicate::Equate(..) |
+                ty::Predicate::WellFormed(..) |
+                ty::Predicate::ObjectSafe(..) |
                 ty::Predicate::TypeOutlives(..) => {
                     // No region bounds here
                 }

src/librustc/middle/implicator.rs

@@ -13,7 +13,7 @@
 use middle::infer::{InferCtxt, GenericKind};
 use middle::subst::Substs;
 use middle::traits;
-use middle::ty::{self, RegionEscape, ToPolyTraitRef, ToPredicate, Ty};
+use middle::ty::{self, RegionEscape, ToPredicate, Ty};
 use middle::ty_fold::{TypeFoldable, TypeFolder};
 
 use syntax::ast;
@@ -278,9 +278,7 @@ impl<'a, 'tcx> Implicator<'a, 'tcx> {
 
         for predicate in predicates.predicates.as_slice() {
             match *predicate {
-                ty::Predicate::Trait(ref data) => {
-                    self.accumulate_from_assoc_types_transitive(data);
-                }
+                ty::Predicate::Trait(..) => { }
                 ty::Predicate::Equate(..) => { }
                 ty::Predicate::Projection(..) => { }
                 ty::Predicate::RegionOutlives(ref data) => {
@@ -301,6 +299,9 @@ impl<'a, 'tcx> Implicator<'a, 'tcx> {
                         }
                     }
                 }
+                ty::Predicate::ObjectSafe(_) |
+                ty::Predicate::WellFormed(_) => {
+                }
             }
         }
 
@@ -349,53 +350,6 @@ impl<'a, 'tcx> Implicator<'a, 'tcx> {
         }
     }
 
-    /// Given that there is a requirement that `Foo<X> : 'a`, where
-    /// `Foo` is declared like `struct Foo<T> where T : SomeTrait`,
-    /// this code finds all the associated types defined in
-    /// `SomeTrait` (and supertraits) and adds a requirement that `<X
-    /// as SomeTrait>::N : 'a` (where `N` is some associated type
-    /// defined in `SomeTrait`). This rule only applies to
-    /// trait-bounds that are not higher-ranked, because we cannot
-    /// project out of a HRTB. This rule helps code using associated
-    /// types to compile, see Issue #22246 for an example.
-    fn accumulate_from_assoc_types_transitive(&mut self,
-                                              data: &ty::PolyTraitPredicate<'tcx>)
-    {
-        debug!("accumulate_from_assoc_types_transitive({:?})",
-               data);
-
-        for poly_trait_ref in traits::supertraits(self.tcx(), data.to_poly_trait_ref()) {
-            match self.tcx().no_late_bound_regions(&poly_trait_ref) {
-                Some(trait_ref) => { self.accumulate_from_assoc_types(trait_ref); }
-                None => { }
-            }
-        }
-    }
-
-    fn accumulate_from_assoc_types(&mut self,
-                                   trait_ref: ty::TraitRef<'tcx>)
-    {
-        debug!("accumulate_from_assoc_types({:?})",
-               trait_ref);
-
-        let trait_def_id = trait_ref.def_id;
-        let trait_def = self.tcx().lookup_trait_def(trait_def_id);
-        let assoc_type_projections: Vec<_> =
-            trait_def.associated_type_names
-                     .iter()
-                     .map(|&name| self.tcx().mk_projection(trait_ref.clone(), name))
-                     .collect();
-        debug!("accumulate_from_assoc_types: assoc_type_projections={:?}",
-               assoc_type_projections);
-        let tys = match self.fully_normalize(&assoc_type_projections) {
-            Ok(tys) => { tys }
-            Err(ErrorReported) => { return; }
-        };
-        for ty in tys {
-            self.accumulate_from_ty(ty);
-        }
-    }
-
     fn accumulate_from_object_ty(&mut self,
                                  ty: Ty<'tcx>,
                                  region_bound: ty::Region,