Auto merge of #55405 - alexcrichton:beta-next, r=pietroalbini

[beta]: Prepare the 1.31.0 beta release

* Update to Cargo's branched 1.31.0 branch
* Update the channel to `beta`

Rolled up beta-accepted PRs:

* #55362: Remove `cargo new --edition` from release notes.
* #55325: Fix link to macros chapter
* #55358: Remove redundant clone (2)
* #55346: Shrink `Statement`.
* #55274: Handle bindings in substructure of patterns with type ascriptions
* #55297: Partial implementation of uniform paths 2.0 to land before beta
* #55192: Fix ordering of nested modules in non-mod.rs mods
* #55185: path suggestions in Rust 2018 should point out the change in semantics
* #55423: back out bogus `Ok`-wrapping suggestion on `?` arm type mismatch

Note that **this does not update the bootstrap compiler** due to #55404

RELEASES.md

@@ -64,9 +64,6 @@ Cargo
 - [`cargo run` doesn't require specifying a package in workspaces.][cargo/5877]
 - [`cargo doc` now supports `--message-format=json`.][cargo/5878] This is
   equivalent to calling `rustdoc --error-format=json`.
-- [You can specify which edition to create a project in cargo
-  with `cargo new --edition`.][cargo/5984] Currently only `2015` is a
-  valid option.
 - [Cargo will now provide a progress bar for builds.][cargo/5995]
 
 Misc
@@ -100,9 +97,8 @@ Misc
 [54404]: https://github.com/rust-lang/rust/pull/54404/
 [cargo/5877]: https://github.com/rust-lang/cargo/pull/5877/
 [cargo/5878]: https://github.com/rust-lang/cargo/pull/5878/
-[cargo/5984]: https://github.com/rust-lang/cargo/pull/5984/
 [cargo/5995]: https://github.com/rust-lang/cargo/pull/5995/
-[proc-macros]: https://doc.rust-lang.org/book/2018-edition/ch19-06-macros.html
+[proc-macros]: https://doc.rust-lang.org/stable/book/2018-edition/ch19-06-macros.html
 
 [`Ipv4Addr::BROADCAST`]: https://doc.rust-lang.org/nightly/std/net/struct.Ipv4Addr.html#associatedconstant.BROADCAST
 [`Ipv4Addr::LOCALHOST`]: https://doc.rust-lang.org/nightly/std/net/struct.Ipv4Addr.html#associatedconstant.LOCALHOST

src/bootstrap/dist.rs

@@ -1447,8 +1447,8 @@ impl Step for Extended {
         tarballs.extend(rls_installer.clone());
         tarballs.extend(clippy_installer.clone());
         tarballs.extend(rustfmt_installer.clone());
-        tarballs.extend(llvm_tools_installer.clone());
-        tarballs.extend(lldb_installer.clone());
+        tarballs.extend(llvm_tools_installer);
+        tarballs.extend(lldb_installer);
         tarballs.push(analysis_installer);
         tarballs.push(std_installer);
         if builder.config.docs {

src/bootstrap/test.rs

@@ -1052,7 +1052,7 @@ impl Step for Compiletest {
         let hostflags = flags.clone();
         cmd.arg("--host-rustcflags").arg(hostflags.join(" "));
 
-        let mut targetflags = flags.clone();
+        let mut targetflags = flags;
         targetflags.push(format!(
             "-Lnative={}",
             builder.test_helpers_out(target).display()

src/ci/run.sh

@@ -51,7 +51,7 @@ fi
 #
 # FIXME: need a scheme for changing this `nightly` value to `beta` and `stable`
 #        either automatically or manually.
-export RUST_RELEASE_CHANNEL=nightly
+export RUST_RELEASE_CHANNEL=beta
 if [ "$DEPLOY$DEPLOY_ALT" != "" ]; then
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --release-channel=$RUST_RELEASE_CHANNEL"
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-llvm-static-stdcpp"

src/librustc/hir/lowering.rs

@@ -3094,7 +3094,8 @@ impl<'a> LoweringContext<'a> {
                 // Privatize the degenerate import base, used only to check
                 // the stability of `use a::{};`, to avoid it showing up as
                 // a re-export by accident when `pub`, e.g. in documentation.
-                let path = P(self.lower_path(id, &prefix, ParamMode::Explicit));
+                let def = self.expect_full_def_from_use(id).next().unwrap_or(Def::Err);
+                let path = P(self.lower_path_extra(def, &prefix, None, ParamMode::Explicit));
                 *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
             }

src/librustc/ich/impls_mir.rs

@@ -606,3 +606,6 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for mir::UserTypeAnnotation<
         }
     }
 }
+
+impl_stable_hash_for!(struct mir::UserTypeProjection<'tcx> { base, projs });
+impl_stable_hash_for!(struct mir::UserTypeProjections<'tcx> { contents });

src/librustc/infer/error_reporting/mod.rs

@@ -479,17 +479,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         err.span_label(arm_span, msg);
                     }
                 }
-                hir::MatchSource::TryDesugar => {
-                    // Issue #51632
-                    if let Ok(try_snippet) = self.tcx.sess.source_map().span_to_snippet(arm_span) {
-                        err.span_suggestion_with_applicability(
-                            arm_span,
-                            "try wrapping with a success variant",
-                            format!("Ok({})", try_snippet),
-                            Applicability::MachineApplicable,
-                        );
-                    }
-                }
+                hir::MatchSource::TryDesugar => {}
                 _ => {
                     let msg = "match arm with an incompatible type";
                     if self.tcx.sess.source_map().is_multiline(arm_span) {

src/librustc/infer/outlives/obligations.rs

@@ -458,7 +458,7 @@ where
             );
             debug!("projection_must_outlive: unique declared bound appears in trait ref");
             self.delegate
-                .push_sub_region_constraint(origin.clone(), region, unique_bound);
+                .push_sub_region_constraint(origin, region, unique_bound);
             return;
         }
 

src/librustc/infer/region_constraints/mod.rs

@@ -749,7 +749,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
                 a // LUB(a,a) = a
             }
 
-            _ => self.combine_vars(tcx, Lub, a, b, origin.clone()),
+            _ => self.combine_vars(tcx, Lub, a, b, origin),
         }
     }
 
@@ -771,7 +771,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
                 a // GLB(a,a) = a
             }
 
-            _ => self.combine_vars(tcx, Glb, a, b, origin.clone()),
+            _ => self.combine_vars(tcx, Glb, a, b, origin),
         }
     }
 

src/librustc/mir/mod.rs

@@ -710,7 +710,7 @@ pub struct LocalDecl<'tcx> {
     /// e.g. via `let x: T`, then we carry that type here. The MIR
     /// borrow checker needs this information since it can affect
     /// region inference.
-    pub user_ty: Option<(UserTypeAnnotation<'tcx>, Span)>,
+    pub user_ty: UserTypeProjections<'tcx>,
 
     /// Name of the local, used in debuginfo and pretty-printing.
     ///
@@ -882,7 +882,7 @@ impl<'tcx> LocalDecl<'tcx> {
         LocalDecl {
             mutability,
             ty,
-            user_ty: None,
+            user_ty: UserTypeProjections::none(),
             name: None,
             source_info: SourceInfo {
                 span,
@@ -903,7 +903,7 @@ impl<'tcx> LocalDecl<'tcx> {
         LocalDecl {
             mutability: Mutability::Mut,
             ty: return_ty,
-            user_ty: None,
+            user_ty: UserTypeProjections::none(),
             source_info: SourceInfo {
                 span,
                 scope: OUTERMOST_SOURCE_SCOPE,
@@ -1674,6 +1674,10 @@ impl<'tcx> Statement<'tcx> {
     /// Changes a statement to a nop. This is both faster than deleting instructions and avoids
     /// invalidating statement indices in `Location`s.
     pub fn make_nop(&mut self) {
+        // `Statement` contributes significantly to peak memory usage. Make
+        // sure it doesn't get bigger.
+        static_assert!(STATEMENT_IS_AT_MOST_56_BYTES: mem::size_of::<Statement<'_>>() <= 56);
+
         self.kind = StatementKind::Nop
     }
 
@@ -1737,7 +1741,7 @@ pub enum StatementKind<'tcx> {
     /// - `Contravariant` -- requires that `T_y :> T`
     /// - `Invariant` -- requires that `T_y == T`
     /// - `Bivariant` -- no effect
-    AscribeUserType(Place<'tcx>, ty::Variance, UserTypeAnnotation<'tcx>),
+    AscribeUserType(Place<'tcx>, ty::Variance, Box<UserTypeProjection<'tcx>>),
 
     /// No-op. Useful for deleting instructions without affecting statement indices.
     Nop,
@@ -1940,6 +1944,10 @@ pub type PlaceProjection<'tcx> = Projection<'tcx, Place<'tcx>, Local, Ty<'tcx>>;
 /// and the index is a local.
 pub type PlaceElem<'tcx> = ProjectionElem<'tcx, Local, Ty<'tcx>>;
 
+/// Alias for projections as they appear in `UserTypeProjection`, where we
+/// need neither the `V` parameter for `Index` nor the `T` for `Field`.
+pub type ProjectionKind<'tcx> = ProjectionElem<'tcx, (), ()>;
+
 newtype_index! {
     pub struct Field {
         DEBUG_FORMAT = "field[{}]"
@@ -2445,6 +2453,117 @@ EnumLiftImpl! {
     }
 }
 
+/// A collection of projections into user types.
+///
+/// They are projections because a binding can occur a part of a
+/// parent pattern that has been ascribed a type.
+///
+/// Its a collection because there can be multiple type ascriptions on
+/// the path from the root of the pattern down to the binding itself.
+///
+/// An example:
+///
+/// ```rust
+/// struct S<'a>((i32, &'a str), String);
+/// let S((_, w): (i32, &'static str), _): S = ...;
+/// //    ------  ^^^^^^^^^^^^^^^^^^^ (1)
+/// //  ---------------------------------  ^ (2)
+/// ```
+///
+/// The highlights labelled `(1)` show the subpattern `(_, w)` being
+/// ascribed the type `(i32, &'static str)`.
+///
+/// The highlights labelled `(2)` show the whole pattern being
+/// ascribed the type `S`.
+///
+/// In this example, when we descend to `w`, we will have built up the
+/// following two projected types:
+///
+///   * base: `S`,                   projection: `(base.0).1`
+///   * base: `(i32, &'static str)`, projection: `base.1`
+///
+/// The first will lead to the constraint `w: &'1 str` (for some
+/// inferred region `'1`). The second will lead to the constraint `w:
+/// &'static str`.
+#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
+pub struct UserTypeProjections<'tcx> {
+    pub(crate) contents: Vec<(UserTypeProjection<'tcx>, Span)>,
+}
+
+BraceStructTypeFoldableImpl! {
+    impl<'tcx> TypeFoldable<'tcx> for UserTypeProjections<'tcx> {
+        contents
+    }
+}
+
+impl<'tcx> UserTypeProjections<'tcx> {
+    pub fn none() -> Self {
+        UserTypeProjections { contents: vec![] }
+    }
+
+    pub fn from_projections(projs: impl Iterator<Item=(UserTypeProjection<'tcx>, Span)>) -> Self {
+        UserTypeProjections { contents: projs.collect() }
+    }
+
+    pub fn projections_and_spans(&self) -> impl Iterator<Item=&(UserTypeProjection<'tcx>, Span)> {
+        self.contents.iter()
+    }
+
+    pub fn projections(&self) -> impl Iterator<Item=&UserTypeProjection<'tcx>> {
+        self.contents.iter().map(|&(ref user_type, _span)| user_type)
+    }
+}
+
+/// Encodes the effect of a user-supplied type annotation on the
+/// subcomponents of a pattern. The effect is determined by applying the
+/// given list of proejctions to some underlying base type. Often,
+/// the projection element list `projs` is empty, in which case this
+/// directly encodes a type in `base`. But in the case of complex patterns with
+/// subpatterns and bindings, we want to apply only a *part* of the type to a variable,
+/// in which case the `projs` vector is used.
+///
+/// Examples:
+///
+/// * `let x: T = ...` -- here, the `projs` vector is empty.
+///
+/// * `let (x, _): T = ...` -- here, the `projs` vector would contain
+///   `field[0]` (aka `.0`), indicating that the type of `s` is
+///   determined by finding the type of the `.0` field from `T`.
+#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
+pub struct UserTypeProjection<'tcx> {
+    pub base: UserTypeAnnotation<'tcx>,
+    pub projs: Vec<ProjectionElem<'tcx, (), ()>>,
+}
+
+impl<'tcx> Copy for ProjectionKind<'tcx> { }
+
+CloneTypeFoldableAndLiftImpls! { ProjectionKind<'tcx>, }
+
+impl<'tcx> TypeFoldable<'tcx> for UserTypeProjection<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        use mir::ProjectionElem::*;
+
+        let base = self.base.fold_with(folder);
+        let projs: Vec<_> = self.projs
+            .iter()
+            .map(|elem| {
+                match elem {
+                    Deref => Deref,
+                    Field(f, ()) => Field(f.clone(), ()),
+                    Index(()) => Index(()),
+                    elem => elem.clone(),
+                }})
+            .collect();
+
+        UserTypeProjection { base, projs }
+    }
+
+    fn super_visit_with<Vs: TypeVisitor<'tcx>>(&self, visitor: &mut Vs) -> bool {
+        self.base.visit_with(visitor)
+        // Note: there's nothing in `self.proj` to visit.
+    }
+}
+
 newtype_index! {
     pub struct Promoted {
         DEBUG_FORMAT = "promoted[{}]"

src/librustc/mir/tcx.rs

@@ -44,11 +44,59 @@ impl<'a, 'gcx, 'tcx> PlaceTy<'tcx> {
         }
     }
 
+    /// `place_ty.field_ty(tcx, f)` computes the type at a given field
+    /// of a record or enum-variant. (Most clients of `PlaceTy` can
+    /// instead just extract the relevant type directly from their
+    /// `PlaceElem`, but some instances of `ProjectionElem<V, T>` do
+    /// not carry a `Ty` for `T`.)
+    ///
+    /// Note that the resulting type has not been normalized.
+    pub fn field_ty(self, tcx: TyCtxt<'a, 'gcx, 'tcx>, f: &Field) -> Ty<'tcx>
+    {
+        // Pass `0` here so it can be used as a "default" variant_index in first arm below
+        let answer = match (self, 0) {
+            (PlaceTy::Ty {
+                ty: &ty::TyS { sty: ty::TyKind::Adt(adt_def, substs), .. } }, variant_index) |
+            (PlaceTy::Downcast { adt_def, substs, variant_index }, _) => {
+                let variant_def = &adt_def.variants[variant_index];
+                let field_def = &variant_def.fields[f.index()];
+                field_def.ty(tcx, substs)
+            }
+            (PlaceTy::Ty { ty }, _) => {
+                match ty.sty {
+                    ty::Tuple(ref tys) => tys[f.index()],
+                    _ => bug!("extracting field of non-tuple non-adt: {:?}", self),
+                }
+            }
+        };
+        debug!("field_ty self: {:?} f: {:?} yields: {:?}", self, f, answer);
+        answer
+    }
+
+    /// Convenience wrapper around `projection_ty_core` for
+    /// `PlaceElem`, where we can just use the `Ty` that is already
+    /// stored inline on field projection elems.
     pub fn projection_ty(self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
                          elem: &PlaceElem<'tcx>)
                          -> PlaceTy<'tcx>
     {
-        match *elem {
+        self.projection_ty_core(tcx, elem, |_, _, ty| ty)
+    }
+
+    /// `place_ty.projection_ty_core(tcx, elem, |...| { ... })`
+    /// projects `place_ty` onto `elem`, returning the appropriate
+    /// `Ty` or downcast variant corresponding to that projection.
+    /// The `handle_field` callback must map a `Field` to its `Ty`,
+    /// (which should be trivial when `T` = `Ty`).
+    pub fn projection_ty_core<V, T>(self,
+                                    tcx: TyCtxt<'a, 'gcx, 'tcx>,
+                                    elem: &ProjectionElem<'tcx, V, T>,
+                                    mut handle_field: impl FnMut(&Self, &Field, &T) -> Ty<'tcx>)
+                                    -> PlaceTy<'tcx>
+    where
+        V: ::std::fmt::Debug, T: ::std::fmt::Debug
+    {
+        let answer = match *elem {
             ProjectionElem::Deref => {
                 let ty = self.to_ty(tcx)
                              .builtin_deref(true)
@@ -94,8 +142,10 @@ impl<'a, 'gcx, 'tcx> PlaceTy<'tcx> {
                         bug!("cannot downcast non-ADT type: `{:?}`", self)
                     }
                 },
-            ProjectionElem::Field(_, fty) => PlaceTy::Ty { ty: fty }
-        }
+            ProjectionElem::Field(ref f, ref fty) => PlaceTy::Ty { ty: handle_field(&self, f, fty) }
+        };
+        debug!("projection_ty self: {:?} elem: {:?} yields: {:?}", self, elem, answer);
+        answer
     }
 }