simplify HR subtyping back to what we did before

A lot of the refactors, however, seem helpful, so leave those in,
particularly since we may want to make this change in the future.

Author: nikomatsakis

src/librustc/diagnostics.rs

@@ -1579,6 +1579,5 @@ register_diagnostics! {
     E0490, // a value of type `..` is borrowed for too long
     E0491, // in type `..`, reference has a longer lifetime than the data it...
     E0495, // cannot infer an appropriate lifetime due to conflicting requirements
-    E0525, // expected a closure that implements `..` but this closure only implements `..`
-    E0526, // skolemization subtype
+    E0525  // expected a closure that implements `..` but this closure only implements `..`
 }

src/librustc/infer/error_reporting.rs

@@ -919,17 +919,6 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     "");
                 err
             }
-            infer::SkolemizeSuccessor(span) => {
-                let mut err =
-                    struct_span_err!(self.tcx.sess, span, E0526,
-                                     "to satisfy higher-ranked bounds, \
-                                      a static lifetime is required");
-                self.tcx.note_and_explain_region(&mut err,
-                    "but the lifetime is only valid for ",
-                    sub,
-                    "");
-                err
-            }
         }
     }
 
@@ -1817,11 +1806,6 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     "...so that references are valid when the destructor \
                      runs");
             }
-            infer::SkolemizeSuccessor(span) => {
-                err.span_note(
-                    span,
-                    "...so that higher-ranked bounds are satisfied");
-            }
         }
     }
 }

src/librustc/infer/higher_ranked/mod.rs

@@ -15,7 +15,6 @@ use super::{CombinedSnapshot,
             InferCtxt,
             LateBoundRegion,
             HigherRankedType,
-            SubregionOrigin,
             SkolemizationMap};
 use super::combine::CombineFields;
 use super::region_inference::{TaintDirections};
@@ -527,7 +526,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             // be itself or other new variables.
             let incoming_taints = self.tainted_regions(snapshot,
                                                        skol,
-                                                       TaintDirections::incoming());
+                                                       TaintDirections::both());
             for &tainted_region in &incoming_taints {
                 // Each skolemized should only be relatable to itself
                 // or new variables:
@@ -568,71 +567,6 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         self.issue_32330_warnings(span, &warnings);
 
-        for (_, &skol) in skol_map {
-            // The outputs from a skolemized variable must all be
-            // equatable with `'static`.
-            let outgoing_taints = self.tainted_regions(snapshot,
-                                                       skol,
-                                                       TaintDirections::outgoing());
-            for &tainted_region in &outgoing_taints {
-                match tainted_region {
-                    ty::ReVar(vid) if new_vars.contains(&vid) => {
-                        // There is a path from a skolemized variable
-                        // to some region variable that doesn't escape
-                        // this snapshot:
-                        //
-                        //    [skol] -> [tainted_region]
-                        //
-                        // We can ignore this. The reasoning relies on
-                        // the fact that the preivous loop
-                        // completed. There are two possible cases
-                        // here.
-                        //
-                        // - `tainted_region` eventually reaches a
-                        //   skolemized variable, which *must* be `skol`
-                        //   (because otherwise we would have already
-                        //   returned `Err`). In that case,
-                        //   `tainted_region` could be inferred to `skol`.
-                        //
-                        // - `tainted_region` never reaches a
-                        //   skolemized variable. In that case, we can
-                        //   safely choose `'static` as an upper bound
-                        //   incoming edges. This is a conservative
-                        //   choice -- the LUB might be one of the
-                        //   incoming skolemized variables, which we
-                        //   might know by ambient bounds. We can
-                        //   consider a more clever choice of upper
-                        //   bound later (modulo some theoretical
-                        //   breakage).
-                        //
-                        // We used to force such `tainted_region` to be
-                        // `'static`, but that leads to problems when
-                        // combined with `plug_leaks`. If you have a case
-                        // where `[skol] -> [tainted_region] -> [skol]`,
-                        // then `plug_leaks` concludes it should replace
-                        // `'static` with a late-bound region, which is
-                        // clearly wrong. (Well, what actually happens is
-                        // you get assertion failures because it WOULD
-                        // have to replace 'static with a late-bound
-                        // region.)
-                    }
-                    ty::ReSkolemized(..) => {
-                        // the only skolemized region we find in the
-                        // successors of X can be X; if there was another
-                        // region Y, then X would have been in the preds
-                        // of Y, and we would have aborted above
-                        assert_eq!(skol, tainted_region);
-                    }
-                    _ => {
-                        self.region_vars.make_subregion(
-                            SubregionOrigin::SkolemizeSuccessor(span),
-                            ty::ReStatic,
-                            tainted_region);
-                    }
-                }
-            }
-        }
-
         Ok(())
     }
 
@@ -682,7 +616,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             skol_map
             .iter()
             .flat_map(|(&skol_br, &skol)| {
-                self.tainted_regions(snapshot, skol, TaintDirections::incoming())
+                self.tainted_regions(snapshot, skol, TaintDirections::both())
                     .into_iter()
                     .map(move |tainted_region| (tainted_region, skol_br))
             })

src/librustc/infer/mod.rs

@@ -335,11 +335,6 @@ pub enum SubregionOrigin<'tcx> {
 
     // Region constraint arriving from destructor safety
     SafeDestructor(Span),
-
-    // When doing a higher-ranked comparison, this region was a
-    // successor from a skolemized region, which means that it must be
-    // `'static` to be sound.
-    SkolemizeSuccessor(Span),
 }
 
 /// Places that type/region parameters can appear.
@@ -1775,7 +1770,6 @@ impl<'tcx> SubregionOrigin<'tcx> {
             AddrOf(a) => a,
             AutoBorrow(a) => a,
             SafeDestructor(a) => a,
-            SkolemizeSuccessor(a) => a,
         }
     }
 }

src/librustc_typeck/astconv.rs

@@ -1699,7 +1699,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                         lint::builtin::HR_LIFETIME_IN_ASSOC_TYPE,
                         ast_ty.id,
                         ast_ty.span,
-                        format!("fn type references lifetime `{}`, \
+                        format!("return type references lifetime `{}`, \
                                  which does not appear in the trait input types",
                                 br_name));
                 }

src/libsyntax/ext/quote.rs

@@ -422,7 +422,7 @@ pub fn expand_quote_expr<'cx>(cx: &'cx mut ExtCtxt,
     base::MacEager::expr(expanded)
 }
 
-pub fn expand_quote_item<'cx>(cx: &mut ExtCtxt,
+pub fn expand_quote_item<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               tts: &[TokenTree])
                               -> Box<base::MacResult+'cx> {

src/libsyntax_ext/concat_idents.rs

@@ -17,7 +17,7 @@ use syntax::parse::token;
 use syntax::parse::token::str_to_ident;
 use syntax::ptr::P;
 
-pub fn expand_syntax_ext<'cx>(cx: &mut ExtCtxt, sp: Span, tts: &[TokenTree])
+pub fn expand_syntax_ext<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[TokenTree])
                               -> Box<base::MacResult+'cx> {
     if !cx.ecfg.enable_concat_idents() {
         feature_gate::emit_feature_err(&cx.parse_sess.span_diagnostic,

src/test/compile-fail/hr-subtype.rs

@@ -52,6 +52,10 @@ macro_rules! check {
             //[bound_inv_a_b_vs_bound_inv_a]~^^^ ERROR mismatched types
             //[bound_a_b_ret_a_vs_bound_a_ret_a]~^^^^ ERROR mismatched types
             //[free_inv_x_vs_free_inv_y]~^^^^^ ERROR mismatched types
+            //[bound_a_b_vs_bound_a]~^^^^^^ ERROR mismatched types
+            //[bound_co_a_b_vs_bound_co_a]~^^^^^^^ ERROR mismatched types
+            //[bound_contra_a_contra_b_ret_co_a]~^^^^^^^^ ERROR mismatched types
+            //[bound_co_a_co_b_ret_contra_a]~^^^^^^^^^ ERROR mismatched types
         }
     }
 }
@@ -87,6 +91,9 @@ check! { free_inv_x_vs_free_inv_y: (fn(Inv<'x>),
 // - if we are covariant, then 'a and 'b can be set to the call-site
 //   intersection;
 // - if we are contravariant, then 'a can be inferred to 'static.
+//
+// FIXME(#32330) this is true, but we are not currently impl'ing this
+// full semantics
 check! { bound_a_b_vs_bound_a: (for<'a,'b> fn(&'a u32, &'b u32),
                                 for<'a>    fn(&'a u32, &'a u32)) }
 check! { bound_co_a_b_vs_bound_co_a: (for<'a,'b> fn(Co<'a>, Co<'b>),
@@ -109,8 +116,4 @@ fn main() {
 //[bound_inv_a_vs_bound_inv_b]~^^^ ERROR compilation successful
 //[bound_co_a_vs_bound_co_b]~^^^^ ERROR compilation successful
 //[free_x_vs_free_x]~^^^^^ ERROR compilation successful
-//[bound_a_b_vs_bound_a]~^^^^^^ ERROR compilation successful
-//[bound_co_a_b_vs_bound_co_a]~^^^^^^^ ERROR compilation successful
-//[bound_contra_a_contra_b_ret_co_a]~^^^^^^^^ ERROR compilation successful
-//[bound_co_a_co_b_ret_contra_a]~^^^^^^^^^ ERROR compilation successful
 }

src/test/compile-fail/regions-trait-1.rs

@@ -24,8 +24,7 @@ impl<'a> get_ctxt for has_ctxt<'a> {
     // Here an error occurs because we used `&self` but
     // the definition used `&`:
     fn get_ctxt(&self) -> &'a ctxt {
-        //~^ ERROR E0308
-        //~| ERROR E0526
+        //~^ ERROR E0053
         self.c
     }