Fix overflow when performing drop check calculations in NLL

src/librustc_mir/borrow_check/nll/type_check/liveness.rs

@@ -15,7 +15,10 @@ use dataflow::move_paths::{HasMoveData, MoveData};
 use rustc::mir::{BasicBlock, Location, Mir};
 use rustc::mir::Local;
 use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
+use rustc::traits;
+use rustc::infer::InferOk;
 use rustc::util::common::ErrorReported;
+use borrow_check::nll::type_check::AtLocation;
 use rustc_data_structures::fx::FxHashSet;
 use syntax::codemap::DUMMY_SP;
 use util::liveness::LivenessResults;
@@ -184,48 +187,86 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
             location
         );
 
-        let tcx = self.cx.infcx.tcx;
-        let mut types = vec![(dropped_ty, 0)];
-        let mut known = FxHashSet();
-        while let Some((ty, depth)) = types.pop() {
-            let span = DUMMY_SP; // FIXME
-            let result = match tcx.dtorck_constraint_for_ty(span, dropped_ty, depth, ty) {
-                Ok(result) => result,
-                Err(ErrorReported) => {
-                    continue;
-                }
-            };
-
-            let ty::DtorckConstraint {
-                outlives,
-                dtorck_types,
-            } = result;
-
-            // All things in the `outlives` array may be touched by
-            // the destructor and must be live at this point.
-            for outlive in outlives {
-                let cause = Cause::DropVar(dropped_local, location);
-                self.push_type_live_constraint(outlive, location, cause);
-            }
+        // If we end visiting the same type twice (usually due to a cycle involving
+        // associated types), we need to ensure that its region types match up with the type
+        // we added to the 'known' map the first time around. For this reason, we need
+        // our infcx to hold onto its calculated region constraints after each call
+        // to dtorck_constraint_for_ty. Otherwise, normalizing the corresponding associated
+        // type will end up instantiating the type with a new set of inference variables
+        // Since this new type will never be in 'known', we end up looping forever.
+        //
+        // For this reason, we avoid calling TypeChecker.normalize, instead doing all normalization
+        // ourselves in one large 'fully_perform_op' callback.
+        let (type_constraints, kind_constraints) = self.cx.fully_perform_op(location.at_self(),
+            |cx| {
+
+            let tcx = cx.infcx.tcx;
+            let mut selcx = traits::SelectionContext::new(cx.infcx);
+            let cause = cx.misc(cx.last_span);
+
+            let mut types = vec![(dropped_ty, 0)];
+            let mut final_obligations = Vec::new();
+            let mut type_constraints = Vec::new();
+            let mut kind_constraints = Vec::new();
 
-            // However, there may also be some types that
-            // `dtorck_constraint_for_ty` could not resolve (e.g.,
-            // associated types and parameters). We need to normalize
-            // associated types here and possibly recursively process.
-            for ty in dtorck_types {
-                let ty = self.cx.normalize(&ty, location);
-                let ty = self.cx.infcx.resolve_type_and_region_vars_if_possible(&ty);
-                match ty.sty {
-                    ty::TyParam(..) | ty::TyProjection(..) | ty::TyAnon(..) => {
-                        let cause = Cause::DropVar(dropped_local, location);
-                        self.push_type_live_constraint(ty, location, cause);
+            let mut known = FxHashSet();
+
+            while let Some((ty, depth)) = types.pop() {
+                let span = DUMMY_SP; // FIXME
+                let result = match tcx.dtorck_constraint_for_ty(span, dropped_ty, depth, ty) {
+                    Ok(result) => result,
+                    Err(ErrorReported) => {
+                        continue;
                     }
+                };
+
+                let ty::DtorckConstraint {
+                    outlives,
+                    dtorck_types,
+                } = result;
+
+                // All things in the `outlives` array may be touched by
+                // the destructor and must be live at this point.
+                for outlive in outlives {
+                    let cause = Cause::DropVar(dropped_local, location);
+                    kind_constraints.push((outlive, location, cause));
+                }
 
-                    _ => if known.insert(ty) {
-                        types.push((ty, depth + 1));
-                    },
+                // However, there may also be some types that
+                // `dtorck_constraint_for_ty` could not resolve (e.g.,
+                // associated types and parameters). We need to normalize
+                // associated types here and possibly recursively process.
+                for ty in dtorck_types {
+                    let traits::Normalized { value: ty, obligations } =
+                        traits::normalize(&mut selcx, cx.param_env, cause.clone(), &ty);
+
+                    final_obligations.extend(obligations);
+
+                    let ty = cx.infcx.resolve_type_and_region_vars_if_possible(&ty);
+                    match ty.sty {
+                        ty::TyParam(..) | ty::TyProjection(..) | ty::TyAnon(..) => {
+                            let cause = Cause::DropVar(dropped_local, location);
+                            type_constraints.push((ty, location, cause));
+                        }
+
+                        _ => if known.insert(ty) {
+                            types.push((ty, depth + 1));
+                        },
+                    }
                 }
             }
+
+            Ok(InferOk {
+                value: (type_constraints, kind_constraints), obligations: final_obligations
+            })
+        }).unwrap();
+
+        for (ty, location, cause) in type_constraints {
+            self.push_type_live_constraint(ty, location, cause);
+        }
+
+        for (kind, location, cause) in kind_constraints {
+            self.push_type_live_constraint(kind, location, cause);
         }
     }
 }

src/test/run-pass/nll/issue-47589.rs

@@ -0,0 +1,33 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(nll)]
+
+pub struct DescriptorSet<'a> {
+    pub slots: Vec<AttachInfo<'a, Resources>>
+}
+
+pub trait ResourcesTrait<'r>: Sized {
+    type DescriptorSet: 'r;
+}
+
+pub struct Resources;
+
+impl<'a> ResourcesTrait<'a> for Resources {
+    type DescriptorSet = DescriptorSet<'a>;
+}
+
+pub enum AttachInfo<'a, R: ResourcesTrait<'a>> {
+    NextDescriptorSet(Box<R::DescriptorSet>)
+}
+
+fn main() {
+    let _x = DescriptorSet {slots: Vec::new()};
+}