Rollup of 9 pull requests

Cargo.toml

@@ -89,6 +89,15 @@ gimli.debug = 0
 miniz_oxide.debug = 0
 object.debug = 0
 
+# The only package that ever uses debug builds is bootstrap.
+# We care a lot about bootstrap's compile times, so don't include debug info for
+# dependencies, only bootstrap itself.
+[profile.dev]
+debug = 0
+[profile.dev.package]
+# Only use debuginfo=1 to further reduce compile times.
+bootstrap.debug = 1
+
 # We want the RLS to use the version of Cargo that we've got vendored in this
 # repository to ensure that the same exact version of Cargo is used by both the
 # RLS and the Cargo binary itself. The RLS depends on Cargo as a git repository

RELEASES.md

@@ -64,7 +64,6 @@ Stabilised APIs
 - [`VecDeque::shrink_to`]
 - [`HashMap::shrink_to`]
 - [`HashSet::shrink_to`]
-- [`task::ready!`]
 
 These APIs are now usable in const contexts:
 
@@ -128,7 +127,6 @@ and related tools.
 [`VecDeque::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/struct.VecDeque.html#method.shrink_to
 [`HashMap::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/hash_map/struct.HashMap.html#method.shrink_to
 [`HashSet::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/hash_set/struct.HashSet.html#method.shrink_to
-[`task::ready!`]: https://doc.rust-lang.org/stable/std/task/macro.ready.html
 [`std::mem::transmute`]: https://doc.rust-lang.org/stable/std/mem/fn.transmute.html
 [`slice::first`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.first
 [`slice::split_first`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_first

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1153,28 +1153,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         .convert_all(data);
     }
 
-    /// Convenient wrapper around `relate_tys::relate_types` -- see
-    /// that fn for docs.
-    fn relate_types(
-        &mut self,
-        a: Ty<'tcx>,
-        v: ty::Variance,
-        b: Ty<'tcx>,
-        locations: Locations,
-        category: ConstraintCategory,
-    ) -> Fallible<()> {
-        relate_tys::relate_types(
-            self.infcx,
-            self.param_env,
-            a,
-            v,
-            b,
-            locations,
-            category,
-            self.borrowck_context,
-        )
-    }
-
     /// Try to relate `sub <: sup`
     fn sub_types(
         &mut self,

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -1,54 +1,44 @@
 use rustc_infer::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelatingDelegate};
-use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin};
+use rustc_infer::infer::NllRegionVariableOrigin;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::relate::TypeRelation;
 use rustc_middle::ty::{self, Const, Ty};
 use rustc_trait_selection::traits::query::Fallible;
 
 use crate::constraints::OutlivesConstraint;
 use crate::diagnostics::UniverseInfo;
-use crate::type_check::{BorrowCheckContext, Locations};
-
-/// Adds sufficient constraints to ensure that `a R b` where `R` depends on `v`:
-///
-/// - "Covariant" `a <: b`
-/// - "Invariant" `a == b`
-/// - "Contravariant" `a :> b`
-///
-/// N.B., the type `a` is permitted to have unresolved inference
-/// variables, but not the type `b`.
-#[instrument(skip(infcx, param_env, borrowck_context), level = "debug")]
-pub(super) fn relate_types<'tcx>(
-    infcx: &InferCtxt<'_, 'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    a: Ty<'tcx>,
-    v: ty::Variance,
-    b: Ty<'tcx>,
-    locations: Locations,
-    category: ConstraintCategory,
-    borrowck_context: &mut BorrowCheckContext<'_, 'tcx>,
-) -> Fallible<()> {
-    TypeRelating::new(
-        infcx,
-        NllTypeRelatingDelegate::new(
-            infcx,
-            borrowck_context,
-            param_env,
-            locations,
-            category,
-            UniverseInfo::relate(a, b),
-        ),
-        v,
-    )
-    .relate(a, b)?;
-    Ok(())
+use crate::type_check::{Locations, TypeChecker};
+
+impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
+    /// Adds sufficient constraints to ensure that `a R b` where `R` depends on `v`:
+    ///
+    /// - "Covariant" `a <: b`
+    /// - "Invariant" `a == b`
+    /// - "Contravariant" `a :> b`
+    ///
+    /// N.B., the type `a` is permitted to have unresolved inference
+    /// variables, but not the type `b`.
+    #[instrument(skip(self), level = "debug")]
+    pub(super) fn relate_types(
+        &mut self,
+        a: Ty<'tcx>,
+        v: ty::Variance,
+        b: Ty<'tcx>,
+        locations: Locations,
+        category: ConstraintCategory,
+    ) -> Fallible<()> {
+        TypeRelating::new(
+            self.infcx,
+            NllTypeRelatingDelegate::new(self, locations, category, UniverseInfo::relate(a, b)),
+            v,
+        )
+        .relate(a, b)?;
+        Ok(())
+    }
 }
 
 struct NllTypeRelatingDelegate<'me, 'bccx, 'tcx> {
-    infcx: &'me InferCtxt<'me, 'tcx>,
-    borrowck_context: &'me mut BorrowCheckContext<'bccx, 'tcx>,
-
-    param_env: ty::ParamEnv<'tcx>,
+    type_checker: &'me mut TypeChecker<'bccx, 'tcx>,
 
     /// Where (and why) is this relation taking place?
     locations: Locations,
@@ -63,25 +53,24 @@ struct NllTypeRelatingDelegate<'me, 'bccx, 'tcx> {
 
 impl NllTypeRelatingDelegate<'me, 'bccx, 'tcx> {
     fn new(
-        infcx: &'me InferCtxt<'me, 'tcx>,
-        borrowck_context: &'me mut BorrowCheckContext<'bccx, 'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
+        type_checker: &'me mut TypeChecker<'bccx, 'tcx>,
         locations: Locations,
         category: ConstraintCategory,
         universe_info: UniverseInfo<'tcx>,
     ) -> Self {
-        Self { infcx, borrowck_context, param_env, locations, category, universe_info }
+        Self { type_checker, locations, category, universe_info }
     }
 }
 
 impl TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx> {
     fn param_env(&self) -> ty::ParamEnv<'tcx> {
-        self.param_env
+        self.type_checker.param_env
     }
 
     fn create_next_universe(&mut self) -> ty::UniverseIndex {
-        let universe = self.infcx.create_next_universe();
-        self.borrowck_context
+        let universe = self.type_checker.infcx.create_next_universe();
+        self.type_checker
+            .borrowck_context
             .constraints
             .universe_causes
             .insert(universe, self.universe_info.clone());
@@ -90,15 +79,18 @@ impl TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx> {
 
     fn next_existential_region_var(&mut self, from_forall: bool) -> ty::Region<'tcx> {
         let origin = NllRegionVariableOrigin::Existential { from_forall };
-        self.infcx.next_nll_region_var(origin)
+        self.type_checker.infcx.next_nll_region_var(origin)
     }
 
     fn next_placeholder_region(&mut self, placeholder: ty::PlaceholderRegion) -> ty::Region<'tcx> {
-        self.borrowck_context.constraints.placeholder_region(self.infcx, placeholder)
+        self.type_checker
+            .borrowck_context
+            .constraints
+            .placeholder_region(self.type_checker.infcx, placeholder)
     }
 
     fn generalize_existential(&mut self, universe: ty::UniverseIndex) -> ty::Region<'tcx> {
-        self.infcx.next_nll_region_var_in_universe(
+        self.type_checker.infcx.next_nll_region_var_in_universe(
             NllRegionVariableOrigin::Existential { from_forall: false },
             universe,
         )
@@ -110,15 +102,17 @@ impl TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx> {
         sub: ty::Region<'tcx>,
         info: ty::VarianceDiagInfo<'tcx>,
     ) {
-        let sub = self.borrowck_context.universal_regions.to_region_vid(sub);
-        let sup = self.borrowck_context.universal_regions.to_region_vid(sup);
-        self.borrowck_context.constraints.outlives_constraints.push(OutlivesConstraint {
-            sup,
-            sub,
-            locations: self.locations,
-            category: self.category,
-            variance_info: info,
-        });
+        let sub = self.type_checker.borrowck_context.universal_regions.to_region_vid(sub);
+        let sup = self.type_checker.borrowck_context.universal_regions.to_region_vid(sup);
+        self.type_checker.borrowck_context.constraints.outlives_constraints.push(
+            OutlivesConstraint {
+                sup,
+                sub,
+                locations: self.locations,
+                category: self.category,
+                variance_info: info,
+            },
+        );
     }
 
     // We don't have to worry about the equality of consts during borrow checking

compiler/rustc_error_codes/src/error_codes.rs

@@ -242,6 +242,7 @@ E0468: include_str!("./error_codes/E0468.md"),
 E0469: include_str!("./error_codes/E0469.md"),
 E0477: include_str!("./error_codes/E0477.md"),
 E0478: include_str!("./error_codes/E0478.md"),
+E0482: include_str!("./error_codes/E0482.md"),
 E0491: include_str!("./error_codes/E0491.md"),
 E0492: include_str!("./error_codes/E0492.md"),
 E0493: include_str!("./error_codes/E0493.md"),
@@ -599,7 +600,6 @@ E0785: include_str!("./error_codes/E0785.md"),
 //  E0479, // the type `..` (provided as the value of a type parameter) is...
 //  E0480, // lifetime of method receiver does not outlive the method call
 //  E0481, // lifetime of function argument does not outlive the function call
-    E0482, // lifetime of return value does not outlive the function call
 //  E0483, // lifetime of operand does not outlive the operation
 //  E0484, // reference is not valid at the time of borrow
 //  E0485, // automatically reference is not valid at the time of borrow

compiler/rustc_error_codes/src/error_codes/E0482.md

@@ -0,0 +1,73 @@
+A lifetime of a returned value does not outlive the function call.
+
+Erroneous code example:
+
+```compile_fail,E0482
+fn prefix<'a>(
+    words: impl Iterator<Item = &'a str>
+) -> impl Iterator<Item = String> { // error!
+    words.map(|v| format!("foo-{}", v))
+}
+```
+
+To fix this error, make the lifetime of the returned value explicit:
+
+```
+fn prefix<'a>(
+    words: impl Iterator<Item = &'a str> + 'a
+) -> impl Iterator<Item = String> + 'a { // ok!
+    words.map(|v| format!("foo-{}", v))
+}
+```
+
+The [`impl Trait`] feature in this example uses an implicit `'static` lifetime
+restriction in the returned type. However the type implementing the `Iterator`
+passed to the function lives just as long as `'a`, which is not long enough.
+
+The solution involves adding lifetime bound to both function argument and
+the return value to make sure that the values inside the iterator
+are not dropped when the function goes out of the scope.
+
+An alternative solution would be to guarantee that the `Item` references
+in the iterator are alive for the whole lifetime of the program.
+
+```
+fn prefix(
+    words: impl Iterator<Item = &'static str>
+) -> impl Iterator<Item = String> {  // ok!
+    words.map(|v| format!("foo-{}", v))
+}
+```
+
+A similar lifetime problem might arise when returning closures:
+
+```compile_fail,E0482
+fn foo(
+    x: &mut Vec<i32>
+) -> impl FnMut(&mut Vec<i32>) -> &[i32] { // error!
+    |y| {
+        y.append(x);
+        y
+    }
+}
+```
+
+Analogically, a solution here is to use explicit return lifetime
+and move the ownership of the variable to the closure.
+
+```
+fn foo<'a>(
+    x: &'a mut Vec<i32>
+) -> impl FnMut(&mut Vec<i32>) -> &[i32] + 'a { // ok!
+    move |y| {
+        y.append(x);
+        y
+    }
+}
+```
+
+To better understand the lifetime treatment in the [`impl Trait`],
+please see the [RFC 1951].
+
+[`impl Trait`]: https://doc.rust-lang.org/reference/types/impl-trait.html
+[RFC 1951]: https://rust-lang.github.io/rfcs/1951-expand-impl-trait.html

compiler/rustc_index/src/vec.rs

@@ -738,6 +738,12 @@ impl<I: Idx, T> IndexVec<I, Option<T>> {
         self.ensure_contains_elem(index, || None);
         self[index].get_or_insert_with(value)
     }
+
+    #[inline]
+    pub fn remove(&mut self, index: I) -> Option<T> {
+        self.ensure_contains_elem(index, || None);
+        self[index].take()
+    }
 }
 
 impl<I: Idx, T: Clone> IndexVec<I, T> {