Auto merge of #44908 - nikomatsakis:beta-20170928, r=alexcrichton

Beta 20170928

Backports of:

- Allow unused extern crate again #44825
- macros: fix bug in collecting trait and impl items with derives. #44757
-  `--cap-lints allow` switches off `can_emit_warnings` #44627
-  Update the libc submodule #44116
- limit and clear cache obligations opportunistically #44269
- clear out projection subobligations after they are processed #43999
-  fix logic error in #44269's `prune_cache_value_obligations` #45065
- REVERTS #43543: Cleanup some remains of `hr_lifetime_in_assoc_type` compatibility lint:

.travis.yml

@@ -97,7 +97,6 @@ matrix:
     - env: IMAGE=dist-arm-linux DEPLOY=1
     - env: IMAGE=dist-armhf-linux DEPLOY=1
     - env: IMAGE=dist-armv7-linux DEPLOY=1
-    - env: IMAGE=dist-fuchsia DEPLOY=1
     - env: IMAGE=dist-i586-gnu-i686-musl DEPLOY=1
     - env: IMAGE=dist-i686-freebsd DEPLOY=1
     - env: IMAGE=dist-i686-linux DEPLOY=1

src/bootstrap/channel.rs

@@ -29,7 +29,7 @@ pub const CFG_RELEASE_NUM: &str = "1.21.0";
 // An optional number to put after the label, e.g. '.2' -> '-beta.2'
 // Be sure to make this starts with a dot to conform to semver pre-release
 // versions (section 9)
-pub const CFG_PRERELEASE_VERSION: &str = ".3";
+pub const CFG_PRERELEASE_VERSION: &str = ".4";
 
 pub struct GitInfo {
     inner: Option<Info>,

src/librustc/ich/impls_ty.rs

@@ -374,6 +374,7 @@ for ty::RegionParameterDef {
             name,
             def_id,
             index,
+            issue_32330: _,
             pure_wrt_drop
         } = *self;
 

src/librustc/infer/error_reporting/mod.rs

@@ -66,7 +66,8 @@ use hir::map as hir_map;
 use hir::def_id::DefId;
 use middle::region;
 use traits::{ObligationCause, ObligationCauseCode};
-use ty::{self, Region, TyCtxt, TypeFoldable};
+use ty::{self, TyCtxt, TypeFoldable};
+use ty::{Region, Issue32330};
 use ty::error::TypeError;
 use syntax::ast::DUMMY_NODE_ID;
 use syntax_pos::{Pos, Span};
@@ -714,6 +715,35 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.tcx.note_and_explain_type_err(diag, terr, span);
     }
 
+    pub fn note_issue_32330(&self,
+                            diag: &mut DiagnosticBuilder<'tcx>,
+                            terr: &TypeError<'tcx>)
+    {
+        debug!("note_issue_32330: terr={:?}", terr);
+        match *terr {
+            TypeError::RegionsInsufficientlyPolymorphic(_, _, Some(box Issue32330 {
+                fn_def_id, region_name
+            })) |
+            TypeError::RegionsOverlyPolymorphic(_, _, Some(box Issue32330 {
+                fn_def_id, region_name
+            })) => {
+                diag.note(
+                    &format!("lifetime parameter `{0}` declared on fn `{1}` \
+                              appears only in the return type, \
+                              but here is required to be higher-ranked, \
+                              which means that `{0}` must appear in both \
+                              argument and return types",
+                             region_name,
+                             self.tcx.item_path_str(fn_def_id)));
+                diag.note(
+                    &format!("this error is the result of a recent bug fix; \
+                              for more information, see issue #33685 \
+                              <https://github.com/rust-lang/rust/issues/33685>"));
+            }
+            _ => {}
+        }
+    }
+
     pub fn report_and_explain_type_error(&self,
                                          trace: TypeTrace<'tcx>,
                                          terr: &TypeError<'tcx>)
@@ -733,6 +763,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }
         };
         self.note_type_err(&mut diag, &trace.cause, None, Some(trace.values), terr);
+        self.note_issue_32330(&mut diag, terr);
         diag
     }
 
@@ -905,7 +936,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 format!(" for lifetime parameter {}in trait containing associated type `{}`",
                         br_string(br), self.tcx.associated_item(def_id).name)
             }
-            infer::EarlyBoundRegion(_, name) => {
+            infer::EarlyBoundRegion(_, name, _) => {
                 format!(" for lifetime parameter `{}`",
                         name)
             }

src/librustc/infer/higher_ranked/mod.rs

@@ -13,7 +13,9 @@
 
 use super::{CombinedSnapshot,
             InferCtxt,
+            LateBoundRegion,
             HigherRankedType,
+            RegionVariableOrigin,
             SubregionOrigin,
             SkolemizationMap};
 use super::combine::CombineFields;
@@ -27,6 +29,15 @@ use util::nodemap::{FxHashMap, FxHashSet};
 
 pub struct HrMatchResult<U> {
     pub value: U,
+
+    /// Normally, when we do a higher-ranked match operation, we
+    /// expect all higher-ranked regions to be constrained as part of
+    /// the match operation. However, in the transition period for
+    /// #32330, it can happen that we sometimes have unconstrained
+    /// regions that get instantiated with fresh variables. In that
+    /// case, we collect the set of unconstrained bound regions here
+    /// and replace them with fresh variables.
+    pub unconstrained_regions: Vec<ty::BoundRegion>,
 }
 
 impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
@@ -97,6 +108,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
     /// that do not appear in `T`. If that happens, those regions are
     /// unconstrained, and this routine replaces them with `'static`.
     pub fn higher_ranked_match<T, U>(&mut self,
+                                     span: Span,
                                      a_pair: &Binder<(T, U)>,
                                      b_match: &T,
                                      a_is_expected: bool)
@@ -146,16 +158,28 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
             // be any region from the sets above, except for other members of
             // `skol_map`. There should always be a representative if things
             // are properly well-formed.
+            let mut unconstrained_regions = vec![];
             let skol_representatives: FxHashMap<_, _> =
                 skol_resolution_map
                 .iter()
-                .map(|(&skol, &(_, ref regions))| {
+                .map(|(&skol, &(br, ref regions))| {
                     let representative =
                         regions.iter()
                                .filter(|&&r| !skol_resolution_map.contains_key(r))
                                .cloned()
                                .next()
-                               .expect("no representative region");
+                               .unwrap_or_else(|| { // [1]
+                                   unconstrained_regions.push(br);
+                                   self.infcx.next_region_var(
+                                       LateBoundRegion(span, br, HigherRankedType))
+                               });
+
+                    // [1] There should always be a representative,
+                    // unless the higher-ranked region did not appear
+                    // in the values being matched. We should reject
+                    // as ill-formed cases that can lead to this, but
+                    // right now we sometimes issue warnings (see
+                    // #32330).
 
                     (skol, representative)
                 })
@@ -192,7 +216,10 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
             // We are now done with these skolemized variables.
             self.infcx.pop_skolemized(skol_map, snapshot);
 
-            Ok(HrMatchResult { value: a_value })
+            Ok(HrMatchResult {
+                value: a_value,
+                unconstrained_regions,
+            })
         });
     }
 
@@ -630,13 +657,28 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                        skol_br,
                        tainted_region);
 
-                return Err(if overly_polymorphic {
+                let issue_32330 = if let &ty::ReVar(vid) = tainted_region {
+                    match self.region_vars.var_origin(vid) {
+                        RegionVariableOrigin::EarlyBoundRegion(_, _, issue_32330) => {
+                            issue_32330.map(Box::new)
+                        }
+                        _ => None
+                    }
+                } else {
+                    None
+                };
+
+                if overly_polymorphic {
                     debug!("Overly polymorphic!");
-                    TypeError::RegionsOverlyPolymorphic(skol_br, tainted_region)
+                    return Err(TypeError::RegionsOverlyPolymorphic(skol_br,
+                                                                   tainted_region,
+                                                                   issue_32330));
                 } else {
                     debug!("Not as polymorphic!");
-                    TypeError::RegionsInsufficientlyPolymorphic(skol_br, tainted_region)
-                })
+                    return Err(TypeError::RegionsInsufficientlyPolymorphic(skol_br,
+                                                                           tainted_region,
+                                                                           issue_32330));
+                }
             }
         }
 

src/librustc/infer/mod.rs

@@ -299,7 +299,7 @@ pub enum RegionVariableOrigin {
     Coercion(Span),
 
     // Region variables created as the values for early-bound regions
-    EarlyBoundRegion(Span, ast::Name),
+    EarlyBoundRegion(Span, ast::Name, Option<ty::Issue32330>),
 
     // Region variables created for bound regions
     // in a function or method that is called
@@ -989,7 +989,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                               span: Span,
                               def: &ty::RegionParameterDef)
                               -> ty::Region<'tcx> {
-        self.next_region_var(EarlyBoundRegion(span, def.name))
+        self.next_region_var(EarlyBoundRegion(span, def.name, def.issue_32330))
     }
 
     /// Create a type inference variable for the given
@@ -1160,6 +1160,18 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         value.fold_with(&mut r)
     }
 
+    /// Returns true if `T` contains unresolved type variables. In the
+    /// process of visiting `T`, this will resolve (where possible)
+    /// type variables in `T`, but it never constructs the final,
+    /// resolved type, so it's more efficient than
+    /// `resolve_type_vars_if_possible()`.
+    pub fn any_unresolved_type_vars<T>(&self, value: &T) -> bool
+        where T: TypeFoldable<'tcx>
+    {
+        let mut r = resolve::UnresolvedTypeFinder::new(self);
+        value.visit_with(&mut r)
+    }
+
     pub fn resolve_type_and_region_vars_if_possible<T>(&self, value: &T) -> T
         where T: TypeFoldable<'tcx>
     {
@@ -1278,13 +1290,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                            -> InferResult<'tcx, HrMatchResult<Ty<'tcx>>>
     {
         let match_pair = match_a.map_bound(|p| (p.projection_ty.trait_ref(self.tcx), p.ty));
+        let span = cause.span;
         let trace = TypeTrace {
             cause,
             values: TraitRefs(ExpectedFound::new(true, match_pair.skip_binder().0, match_b))
         };
 
         let mut combine = self.combine_fields(trace, param_env);
-        let result = combine.higher_ranked_match(&match_pair, &match_b, true)?;
+        let result = combine.higher_ranked_match(span, &match_pair, &match_b, true)?;
         Ok(InferOk { value: result, obligations: combine.obligations })
     }
 

src/librustc/infer/resolve.rs

@@ -10,7 +10,7 @@
 
 use super::{InferCtxt, FixupError, FixupResult};
 use ty::{self, Ty, TyCtxt, TypeFoldable};
-use ty::fold::TypeFolder;
+use ty::fold::{TypeFolder, TypeVisitor};
 
 ///////////////////////////////////////////////////////////////////////////
 // OPPORTUNISTIC TYPE RESOLVER
@@ -80,6 +80,43 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for OpportunisticTypeAndRegionResolv
     }
 }
 
+///////////////////////////////////////////////////////////////////////////
+// UNRESOLVED TYPE FINDER
+
+/// The unresolved type **finder** walks your type and searches for
+/// type variables that don't yet have a value. They get pushed into a
+/// vector. It does not construct the fully resolved type (which might
+/// involve some hashing and so forth).
+pub struct UnresolvedTypeFinder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
+    infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
+}
+
+impl<'a, 'gcx, 'tcx> UnresolvedTypeFinder<'a, 'gcx, 'tcx> {
+    pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>) -> Self {
+        UnresolvedTypeFinder { infcx }
+    }
+}
+
+impl<'a, 'gcx, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'gcx, 'tcx> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
+        let t = self.infcx.shallow_resolve(t);
+        if t.has_infer_types() {
+            if let ty::TyInfer(_) = t.sty {
+                // Since we called `shallow_resolve` above, this must
+                // be an (as yet...) unresolved inference variable.
+                true
+            } else {
+                // Otherwise, visit its contents.
+                t.super_visit_with(self)
+            }
+        } else {
+            // Micro-optimize: no inference types at all Can't have unresolved type
+            // variables, no need to visit the contents.
+            false
+        }
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // FULL TYPE RESOLUTION
 

src/librustc/lint/builtin.rs

@@ -30,7 +30,7 @@ declare_lint! {
 
 declare_lint! {
     pub UNUSED_EXTERN_CRATES,
-    Warn,
+    Allow,
     "extern crates that are never used"
 }