Merge pull request rust-lang#31851 from nikomatsakis/backport-pr-31349

Revert ObligationForest on beta branch

Author: brson

src/librustc/diagnostics.rs

@@ -679,43 +679,6 @@ There's no easy fix for this, generally code will need to be refactored so that
 you no longer need to derive from `Super<Self>`.
 "####,
 
-E0072: r##"
-When defining a recursive struct or enum, any use of the type being defined
-from inside the definition must occur behind a pointer (like `Box` or `&`).
-This is because structs and enums must have a well-defined size, and without
-the pointer the size of the type would need to be unbounded.
-
-Consider the following erroneous definition of a type for a list of bytes:
-
-```
-// error, invalid recursive struct type
-struct ListNode {
-    head: u8,
-    tail: Option<ListNode>,
-}
-```
-
-This type cannot have a well-defined size, because it needs to be arbitrarily
-large (since we would be able to nest `ListNode`s to any depth). Specifically,
-
-```plain
-size of `ListNode` = 1 byte for `head`
-                   + 1 byte for the discriminant of the `Option`
-                   + size of `ListNode`
-```
-
-One way to fix this is by wrapping `ListNode` in a `Box`, like so:
-
-```
-struct ListNode {
-    head: u8,
-    tail: Option<Box<ListNode>>,
-}
-```
-
-This works because `Box` is a pointer, so its size is well-known.
-"##,
-
 E0109: r##"
 You tried to give a type parameter to a type which doesn't need it. Erroneous
 code example:

src/librustc/middle/check_const.rs

@@ -125,7 +125,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
             None => self.tcx.empty_parameter_environment()
         };
 
-        let infcx = infer::new_infer_ctxt(self.tcx, &self.tcx.tables, Some(param_env));
+        let infcx = infer::new_infer_ctxt(self.tcx, &self.tcx.tables, Some(param_env), false);
 
         f(&mut euv::ExprUseVisitor::new(self, &infcx))
     }
@@ -280,7 +280,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
 
     fn check_static_type(&self, e: &hir::Expr) {
         let ty = self.tcx.node_id_to_type(e.id);
-        let infcx = infer::new_infer_ctxt(self.tcx, &self.tcx.tables, None);
+        let infcx = infer::new_infer_ctxt(self.tcx, &self.tcx.tables, None, false);
         let cause = traits::ObligationCause::new(e.span, e.id, traits::SharedStatic);
         let mut fulfill_cx = infcx.fulfillment_cx.borrow_mut();
         fulfill_cx.register_builtin_bound(&infcx, ty, ty::BoundSync, cause);

src/librustc/middle/check_match.rs

@@ -1095,7 +1095,8 @@ fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
                         //FIXME: (@jroesch) this code should be floated up as well
                         let infcx = infer::new_infer_ctxt(cx.tcx,
                                                           &cx.tcx.tables,
-                                                          Some(cx.param_env.clone()));
+                                                          Some(cx.param_env.clone()),
+                                                          false);
                         if infcx.type_moves_by_default(pat_ty, pat.span) {
                             check_move(p, sub.as_ref().map(|p| &**p));
                         }
@@ -1127,7 +1128,8 @@ fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>,
 
     let infcx = infer::new_infer_ctxt(cx.tcx,
                                       &cx.tcx.tables,
-                                      Some(checker.cx.param_env.clone()));
+                                      Some(checker.cx.param_env.clone()),
+                                      false);
 
     let mut visitor = ExprUseVisitor::new(&mut checker, &infcx);
     visitor.walk_expr(guard);

src/librustc/middle/check_rvalues.rs

@@ -44,7 +44,8 @@ impl<'a, 'tcx, 'v> intravisit::Visitor<'v> for RvalueContext<'a, 'tcx> {
             let param_env = ParameterEnvironment::for_item(self.tcx, fn_id);
             let infcx = infer::new_infer_ctxt(self.tcx,
                                               &self.tcx.tables,
-                                              Some(param_env.clone()));
+                                              Some(param_env.clone()),
+                                              false);
             let mut delegate = RvalueContextDelegate { tcx: self.tcx, param_env: &param_env };
             let mut euv = euv::ExprUseVisitor::new(&mut delegate, &infcx);
             euv.walk_fn(fd, b);

src/librustc/middle/const_eval.rs

@@ -1248,7 +1248,7 @@ fn resolve_trait_associated_const<'a, 'tcx: 'a>(tcx: &'a ty::ctxt<'tcx>,
                                               substs: trait_substs });
 
     tcx.populate_implementations_for_trait_if_necessary(trait_ref.def_id());
-    let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None);
+    let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None, false);
 
     let mut selcx = traits::SelectionContext::new(&infcx);
     let obligation = traits::Obligation::new(traits::ObligationCause::dummy(),

src/librustc/middle/infer/mod.rs

@@ -354,9 +354,16 @@ pub fn fixup_err_to_string(f: FixupError) -> String {
     }
 }
 
+/// errors_will_be_reported is required to proxy to the fulfillment context
+/// FIXME -- a better option would be to hold back on modifying
+/// the global cache until we know that all dependent obligations
+/// are also satisfied. In that case, we could actually remove
+/// this boolean flag, and we'd also avoid the problem of squelching
+/// duplicate errors that occur across fns.
 pub fn new_infer_ctxt<'a, 'tcx>(tcx: &'a ty::ctxt<'tcx>,
                                 tables: &'a RefCell<ty::Tables<'tcx>>,
-                                param_env: Option<ty::ParameterEnvironment<'a, 'tcx>>)
+                                param_env: Option<ty::ParameterEnvironment<'a, 'tcx>>,
+                                errors_will_be_reported: bool)
                                 -> InferCtxt<'a, 'tcx> {
     InferCtxt {
         tcx: tcx,
@@ -366,7 +373,7 @@ pub fn new_infer_ctxt<'a, 'tcx>(tcx: &'a ty::ctxt<'tcx>,
         float_unification_table: RefCell::new(UnificationTable::new()),
         region_vars: RegionVarBindings::new(tcx),
         parameter_environment: param_env.unwrap_or(tcx.empty_parameter_environment()),
-        fulfillment_cx: RefCell::new(traits::FulfillmentContext::new()),
+        fulfillment_cx: RefCell::new(traits::FulfillmentContext::new(errors_will_be_reported)),
         reported_trait_errors: RefCell::new(FnvHashSet()),
         normalize: false,
         err_count_on_creation: tcx.sess.err_count()
@@ -376,7 +383,7 @@ pub fn new_infer_ctxt<'a, 'tcx>(tcx: &'a ty::ctxt<'tcx>,
 pub fn normalizing_infer_ctxt<'a, 'tcx>(tcx: &'a ty::ctxt<'tcx>,
                                         tables: &'a RefCell<ty::Tables<'tcx>>)
                                         -> InferCtxt<'a, 'tcx> {
-    let mut infcx = new_infer_ctxt(tcx, tables, None);
+    let mut infcx = new_infer_ctxt(tcx, tables, None, false);
     infcx.normalize = true;
     infcx
 }
@@ -515,7 +522,7 @@ pub fn normalize_associated_type<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> T
         return value;
     }
 
-    let infcx = new_infer_ctxt(tcx, &tcx.tables, None);
+    let infcx = new_infer_ctxt(tcx, &tcx.tables, None, true);
     let mut selcx = traits::SelectionContext::new(&infcx);
     let cause = traits::ObligationCause::dummy();
     let traits::Normalized { value: result, obligations } =

src/librustc/middle/traits/error_reporting.rs

@@ -182,8 +182,7 @@ fn report_on_unimplemented<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 /// if the program type checks or not -- and they are unusual
 /// occurrences in any case.
 pub fn report_overflow_error<'a, 'tcx, T>(infcx: &InferCtxt<'a, 'tcx>,
-                                          obligation: &Obligation<'tcx, T>,
-                                          suggest_increasing_limit: bool)
+                                          obligation: &Obligation<'tcx, T>)
                                           -> !
     where T: fmt::Display + TypeFoldable<'tcx>
 {
@@ -193,9 +192,7 @@ pub fn report_overflow_error<'a, 'tcx, T>(infcx: &InferCtxt<'a, 'tcx>,
                                    "overflow evaluating the requirement `{}`",
                                    predicate);
 
-    if suggest_increasing_limit {
-        suggest_new_overflow_limit(infcx.tcx, &mut err, obligation.cause.span);
-    }
+    suggest_new_overflow_limit(infcx.tcx, &mut err, obligation.cause.span);
 
     note_obligation_cause(infcx, &mut err, obligation);
 
@@ -204,142 +201,6 @@ pub fn report_overflow_error<'a, 'tcx, T>(infcx: &InferCtxt<'a, 'tcx>,
     unreachable!();
 }
 
-/// Reports that a cycle was detected which led to overflow and halts
-/// compilation. This is equivalent to `report_overflow_error` except
-/// that we can give a more helpful error message (and, in particular,
-/// we do not suggest increasing the overflow limit, which is not
-/// going to help).
-pub fn report_overflow_error_cycle<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
-                                             cycle: &Vec<PredicateObligation<'tcx>>)
-                                             -> !
-{
-    assert!(cycle.len() > 1);
-
-    debug!("report_overflow_error_cycle(cycle length = {})", cycle.len());
-
-    let cycle = infcx.resolve_type_vars_if_possible(cycle);
-
-    debug!("report_overflow_error_cycle: cycle={:?}", cycle);
-
-    assert_eq!(&cycle[0].predicate, &cycle.last().unwrap().predicate);
-
-    try_report_overflow_error_type_of_infinite_size(infcx, &cycle);
-    report_overflow_error(infcx, &cycle[0], false);
-}
-
-/// If a cycle results from evaluated whether something is Sized, that
-/// is a particular special case that always results from a struct or
-/// enum definition that lacks indirection (e.g., `struct Foo { x: Foo
-/// }`). We wish to report a targeted error for this case.
-pub fn try_report_overflow_error_type_of_infinite_size<'a, 'tcx>(
-    infcx: &InferCtxt<'a, 'tcx>,
-    cycle: &[PredicateObligation<'tcx>])
-{
-    let sized_trait = match infcx.tcx.lang_items.sized_trait() {
-        Some(v) => v,
-        None => return,
-    };
-    let top_is_sized = {
-        match cycle[0].predicate {
-            ty::Predicate::Trait(ref data) => data.def_id() == sized_trait,
-            _ => false,
-        }
-    };
-    if !top_is_sized {
-        return;
-    }
-
-    // The only way to have a type of infinite size is to have,
-    // somewhere, a struct/enum type involved. Identify all such types
-    // and report the cycle to the user.
-
-    let struct_enum_tys: Vec<_> =
-        cycle.iter()
-             .flat_map(|obligation| match obligation.predicate {
-                 ty::Predicate::Trait(ref data) => {
-                     assert_eq!(data.def_id(), sized_trait);
-                     let self_ty = data.skip_binder().trait_ref.self_ty(); // (*)
-                     // (*) ok to skip binder because this is just
-                     // error reporting and regions don't really
-                     // matter
-                     match self_ty.sty {
-                         ty::TyEnum(..) | ty::TyStruct(..) => Some(self_ty),
-                         _ => None,
-                     }
-                 }
-                 _ => {
-                     infcx.tcx.sess.span_bug(obligation.cause.span,
-                                             &format!("Sized cycle involving non-trait-ref: {:?}",
-                                                      obligation.predicate));
-                 }
-             })
-             .collect();
-
-    assert!(!struct_enum_tys.is_empty());
-
-    // This is a bit tricky. We want to pick a "main type" in the
-    // listing that is local to the current crate, so we can give a
-    // good span to the user. But it might not be the first one in our
-    // cycle list. So find the first one that is local and then
-    // rotate.
-    let (main_index, main_def_id) =
-        struct_enum_tys.iter()
-                       .enumerate()
-                       .filter_map(|(index, ty)| match ty.sty {
-                           ty::TyEnum(adt_def, _) | ty::TyStruct(adt_def, _)
-                               if adt_def.did.is_local() =>
-                               Some((index, adt_def.did)),
-                           _ =>
-                               None,
-                       })
-                       .next()
-                       .unwrap(); // should always be SOME local type involved!
-
-    // Rotate so that the "main" type is at index 0.
-    let struct_enum_tys: Vec<_> =
-        struct_enum_tys.iter()
-                       .cloned()
-                       .skip(main_index)
-                       .chain(struct_enum_tys.iter().cloned().take(main_index))
-                       .collect();
-
-    let tcx = infcx.tcx;
-    let mut err = recursive_type_with_infinite_size_error(tcx, main_def_id);
-    let len = struct_enum_tys.len();
-    if len > 2 {
-        let span = tcx.map.span_if_local(main_def_id).unwrap();
-        err.fileline_note(span,
-                          &format!("type `{}` is embedded within `{}`...",
-                                   struct_enum_tys[0],
-                                   struct_enum_tys[1]));
-        for &next_ty in &struct_enum_tys[1..len-1] {
-            err.fileline_note(span,
-                              &format!("...which in turn is embedded within `{}`...", next_ty));
-        }
-        err.fileline_note(span,
-                          &format!("...which in turn is embedded within `{}`, \
-                                    completing the cycle.",
-                                   struct_enum_tys[len-1]));
-    }
-    err.emit();
-    infcx.tcx.sess.abort_if_errors();
-    unreachable!();
-}
-
-pub fn recursive_type_with_infinite_size_error<'tcx>(tcx: &ty::ctxt<'tcx>,
-                                                     type_def_id: DefId)
-                                                     -> DiagnosticBuilder<'tcx>
-{
-    assert!(type_def_id.is_local());
-    let span = tcx.map.span_if_local(type_def_id).unwrap();
-    let mut err = struct_span_err!(tcx.sess, span, E0072, "recursive type `{}` has infinite size",
-                                   tcx.item_path_str(type_def_id));
-    err.fileline_help(span, &format!("insert indirection (e.g., a `Box`, `Rc`, or `&`) \
-                                      at some point to make `{}` representable",
-                                     tcx.item_path_str(type_def_id)));
-    err
-}
-
 pub fn report_selection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
                                         obligation: &PredicateObligation<'tcx>,
                                         error: &SelectionError<'tcx>)