Auto merge of #72768 - JohnTitor:rollup-6kwokh6, r=JohnTitor

Rollup of 10 pull requests

Successful merges:

 - #72033 (Update RELEASES.md for 1.44.0)
 - #72162 (Add Extend::{extend_one,extend_reserve})
 - #72419 (Miri read_discriminant: return a scalar instead of raw underlying bytes)
 - #72621 (Don't bail out of trait selection when predicate references an error)
 - #72677 (Fix diagnostics for `@ ..` binding pattern in tuples and tuple structs)
 - #72710 (Add test to make sure -Wunused-crate-dependencies works with tests)
 - #72724 (Revert recursive `TokenKind::Interpolated` expansion for now)
 - #72741 (Remove unused mut from long-linker-command-lines test)
 - #72750 (Remove remaining calls to `as_local_node_id`)
 - #72752 (remove mk_bool)

Failed merges:

r? @ghost

Cargo.lock

@@ -4144,7 +4144,6 @@ dependencies = [
  "rustc_lexer",
  "rustc_session",
  "rustc_span",
- "smallvec 1.4.0",
  "unicode-normalization",
 ]
 

RELEASES.md

@@ -1,3 +1,163 @@
+Version 1.44.0 (2020-06-04)
+==========================
+
+Language
+--------
+- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
+- [Added the `unused_braces` lint.][70081]
+
+**Syntax-only changes**
+
+- [Expansion-driven outline module parsing][69838]
+```rust
+#[cfg(FALSE)]
+mod foo {
+    mod bar {
+        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
+    }
+}
+```
+
+These are still rejected semantically, so you will likely receive an error but
+these changes can be seen and parsed by macros and conditional compilation.
+
+Compiler
+--------
+- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
+  Additionally when in incremental mode rustc defaults to 256 codegen units.
+- [Refactored `catch_unwind`, to have zero-cost unless unwinding is enabled and
+  a panic is thrown.][67502]
+- [Added tier 3\* support for the `aarch64-unknown-none` and
+  `aarch64-unknown-none-softfloat` targets.][68334]
+- [Added tier 3 support for `arm64-apple-tvos` and
+  `x86_64-apple-tvos` targets.][68191]
+
+
+Libraries
+---------
+- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
+  `vec![]` to be able to be used in `const` contexts.
+- [`convert::Infallible` now implements `Hash`.][70281]
+- [`OsString` now implements `DerefMut` and `IndexMut` returning
+  a `&mut OsStr`.][70048]
+- [Unicode 13 is now supported.][69929]
+- [`String` now implements `From<&mut str>`.][69661]
+- [`IoSlice` now implements `Copy`.][69403]
+- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is less than 32.
+- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
+- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
+  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
+  integer types.][69373]
+
+Stabilized APIs
+---------------
+- [`PathBuf::with_capacity`]
+- [`PathBuf::capacity`]
+- [`PathBuf::clear`]
+- [`PathBuf::reserve`]
+- [`PathBuf::reserve_exact`]
+- [`PathBuf::shrink_to_fit`]
+- [`f32::to_int_unchecked`]
+- [`f64::to_int_unchecked`]
+- [`Layout::align_to`]
+- [`Layout::pad_to_align`]
+- [`Layout::array`]
+- [`Layout::extend`]
+
+Cargo
+-----
+- [Added the `cargo tree` command which will print a tree graph of
+  your dependencies.][cargo/8062] E.g.
+  ```
+    mdbook v0.3.2 (/Users/src/rust/mdbook)
+  ├── ammonia v3.0.0
+  │   ├── html5ever v0.24.0
+  │   │   ├── log v0.4.8
+  │   │   │   └── cfg-if v0.1.9
+  │   │   ├── mac v0.1.1
+  │   │   └── markup5ever v0.9.0
+  │   │       ├── log v0.4.8 (*)
+  │   │       ├── phf v0.7.24
+  │   │       │   └── phf_shared v0.7.24
+  │   │       │       ├── siphasher v0.2.3
+  │   │       │       └── unicase v1.4.2
+  │   │       │           [build-dependencies]
+  │   │       │           └── version_check v0.1.5
+  ...
+  ```
+
+Misc
+----
+- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
+  the version in the sidebar.][69494]
+
+Compatibility Notes
+-------------------
+- [Rustc now correctly generates static libraries on Windows GNU targets with
+  the `.a` extension, rather than the previous `.lib`.][70937]
+- [Removed the `-C no_integrated_as` flag from rustc.][70345]
+- [The `file_name` property in JSON output of macro errors now points the actual
+  source file rather than the previous format of `<NAME macros>`.][70969]
+  **Note:** this may not point a file that actually exists on the user's system.
+- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
+- [`mem::{zeroed, uninitialised, MaybeUninit}` will now panic when used with types
+  that do not allow zero initialization such as `NonZeroU8`.][66059] This was
+  previously a warning.
+- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
+  operator has been defined as a saturating operation.][71269] This was previously
+  undefined behaviour, you can use the `{f64, f32}::to_int_unchecked` methods to
+  continue using the current behaviour which may desirable in rare performance
+  sensitive situations.
+
+Internal Only
+-------------
+These changes provide no direct user facing benefits, but represent significant
+improvements to the internals and overall performance of rustc and
+related tools.
+
+- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
+- [Replace big JS dict with JSON parsing.][71250]
+
+[69373]: https://github.com/rust-lang/rust/pull/69373/
+[66059]: https://github.com/rust-lang/rust/pull/66059/
+[68191]: https://github.com/rust-lang/rust/pull/68191/
+[68899]: https://github.com/rust-lang/rust/pull/68899/
+[71147]: https://github.com/rust-lang/rust/pull/71147/
+[71250]: https://github.com/rust-lang/rust/pull/71250/
+[70937]: https://github.com/rust-lang/rust/pull/70937/
+[70969]: https://github.com/rust-lang/rust/pull/70969/
+[70632]: https://github.com/rust-lang/rust/pull/70632/
+[70281]: https://github.com/rust-lang/rust/pull/70281/
+[70345]: https://github.com/rust-lang/rust/pull/70345/
+[70048]: https://github.com/rust-lang/rust/pull/70048/
+[70081]: https://github.com/rust-lang/rust/pull/70081/
+[70156]: https://github.com/rust-lang/rust/pull/70156/
+[71269]: https://github.com/rust-lang/rust/pull/71269/
+[69838]: https://github.com/rust-lang/rust/pull/69838/
+[69929]: https://github.com/rust-lang/rust/pull/69929/
+[69661]: https://github.com/rust-lang/rust/pull/69661/
+[69778]: https://github.com/rust-lang/rust/pull/69778/
+[69494]: https://github.com/rust-lang/rust/pull/69494/
+[69403]: https://github.com/rust-lang/rust/pull/69403/
+[69033]: https://github.com/rust-lang/rust/pull/69033/
+[68692]: https://github.com/rust-lang/rust/pull/68692/
+[68334]: https://github.com/rust-lang/rust/pull/68334/
+[67502]: https://github.com/rust-lang/rust/pull/67502/
+[cargo/8062]: https://github.com/rust-lang/cargo/pull/8062/
+[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
+[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
+[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
+[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
+[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
+[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
+[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
+[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
+[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
+[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
+[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
+[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
+
+
 Version 1.43.1 (2020-05-07)
 ===========================
 

src/liballoc/collections/binary_heap.rs

@@ -1376,6 +1376,16 @@ impl<T: Ord> Extend<T> for BinaryHeap<T> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         <Self as SpecExtend<I>>::spec_extend(self, iter);
     }
+
+    #[inline]
+    fn extend_one(&mut self, item: T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 impl<T: Ord, I: IntoIterator<Item = T>> SpecExtend<I> for BinaryHeap<T> {
@@ -1406,4 +1416,14 @@ impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &item: &'a T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }

src/liballoc/collections/btree/map.rs

@@ -1901,6 +1901,11 @@ impl<K: Ord, V> Extend<(K, V)> for BTreeMap<K, V> {
             self.insert(k, v);
         });
     }
+
+    #[inline]
+    fn extend_one(&mut self, (k, v): (K, V)) {
+        self.insert(k, v);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -1908,6 +1913,11 @@ impl<'a, K: Ord + Copy, V: Copy> Extend<(&'a K, &'a V)> for BTreeMap<K, V> {
     fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: I) {
         self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
     }
+
+    #[inline]
+    fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
+        self.insert(k, v);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/liballoc/collections/btree/set.rs

@@ -1152,6 +1152,11 @@ impl<T: Ord> Extend<T> for BTreeSet<T> {
             self.insert(elem);
         });
     }
+
+    #[inline]
+    fn extend_one(&mut self, elem: T) {
+        self.insert(elem);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -1159,6 +1164,11 @@ impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BTreeSet<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &elem: &'a T) {
+        self.insert(elem);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/liballoc/collections/linked_list.rs

@@ -1748,6 +1748,11 @@ impl<T> Extend<T> for LinkedList<T> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         <Self as SpecExtend<I>>::spec_extend(self, iter);
     }
+
+    #[inline]
+    fn extend_one(&mut self, elem: T) {
+        self.push_back(elem);
+    }
 }
 
 impl<I: IntoIterator> SpecExtend<I> for LinkedList<I::Item> {
@@ -1767,6 +1772,11 @@ impl<'a, T: 'a + Copy> Extend<&'a T> for LinkedList<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &elem: &'a T) {
+        self.push_back(elem);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/liballoc/collections/vec_deque.rs

@@ -2881,6 +2881,16 @@ impl<A> Extend<A> for VecDeque<A> {
             }
         }
     }
+
+    #[inline]
+    fn extend_one(&mut self, elem: A) {
+        self.push_back(elem);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -2888,6 +2898,16 @@ impl<'a, T: 'a + Copy> Extend<&'a T> for VecDeque<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &elem: &T) {
+        self.push_back(elem);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/liballoc/lib.rs

@@ -93,6 +93,7 @@
 #![feature(container_error_extra)]
 #![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
+#![feature(extend_one)]
 #![feature(fmt_internals)]
 #![feature(fn_traits)]
 #![feature(fundamental)]

src/liballoc/string.rs

@@ -1799,6 +1799,16 @@ impl Extend<char> for String {
         self.reserve(lower_bound);
         iterator.for_each(move |c| self.push(c));
     }
+
+    #[inline]
+    fn extend_one(&mut self, c: char) {
+        self.push(c);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "extend_ref", since = "1.2.0")]
@@ -1806,6 +1816,16 @@ impl<'a> Extend<&'a char> for String {
     fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &c: &'a char) {
+        self.push(c);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1813,6 +1833,11 @@ impl<'a> Extend<&'a str> for String {
     fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |s| self.push_str(s));
     }
+
+    #[inline]
+    fn extend_one(&mut self, s: &'a str) {
+        self.push_str(s);
+    }
 }
 
 #[stable(feature = "extend_string", since = "1.4.0")]
@@ -1820,6 +1845,11 @@ impl Extend<String> for String {
     fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |s| self.push_str(&s));
     }
+
+    #[inline]
+    fn extend_one(&mut self, s: String) {
+        self.push_str(&s);
+    }
 }
 
 #[stable(feature = "herd_cows", since = "1.19.0")]
@@ -1827,6 +1857,11 @@ impl<'a> Extend<Cow<'a, str>> for String {
     fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |s| self.push_str(&s));
     }
+
+    #[inline]
+    fn extend_one(&mut self, s: Cow<'a, str>) {
+        self.push_str(&s);
+    }
 }
 
 /// A convenience impl that delegates to the impl for `&str`.

src/liballoc/vec.rs

@@ -2045,6 +2045,16 @@ impl<T> Extend<T> for Vec<T> {
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
     }
+
+    #[inline]
+    fn extend_one(&mut self, item: T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 // Specialization trait used for Vec::from_iter and Vec::extend
@@ -2316,6 +2326,16 @@ impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.spec_extend(iter.into_iter())
     }
+
+    #[inline]
+    fn extend_one(&mut self, &item: &'a T) {
+        self.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.reserve(additional);
+    }
 }
 
 macro_rules! __impl_slice_eq1 {

src/libcore/iter/traits/collect.rs

@@ -322,7 +322,7 @@ impl<I: Iterator> IntoIterator for I {
 pub trait Extend<A> {
     /// Extends a collection with the contents of an iterator.
     ///
-    /// As this is the only method for this trait, the [trait-level] docs
+    /// As this is the only required method for this trait, the [trait-level] docs
     /// contain more details.
     ///
     /// [trait-level]: trait.Extend.html
@@ -341,6 +341,20 @@ pub trait Extend<A> {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn extend<T: IntoIterator<Item = A>>(&mut self, iter: T);
+
+    /// Extends a collection with exactly one element.
+    #[unstable(feature = "extend_one", issue = "72631")]
+    fn extend_one(&mut self, item: A) {
+        self.extend(Some(item));
+    }
+
+    /// Reserves capacity in a collection for the given number of additional elements.
+    ///
+    /// The default implementation does nothing.
+    #[unstable(feature = "extend_one", issue = "72631")]
+    fn extend_reserve(&mut self, additional: usize) {
+        let _ = additional;
+    }
 }
 
 #[stable(feature = "extend_for_unit", since = "1.28.0")]
@@ -348,4 +362,5 @@ impl Extend<()> for () {
     fn extend<T: IntoIterator<Item = ()>>(&mut self, iter: T) {
         iter.into_iter().for_each(drop)
     }
+    fn extend_one(&mut self, _item: ()) {}
 }

src/libcore/iter/traits/iterator.rs

@@ -1711,9 +1711,9 @@ pub trait Iterator {
         ) -> impl FnMut((), T) + 'a {
             move |(), x| {
                 if f(&x) {
-                    left.extend(Some(x));
+                    left.extend_one(x);
                 } else {
-                    right.extend(Some(x));
+                    right.extend_one(x);
                 }
             }
         }
@@ -2686,14 +2686,20 @@ pub trait Iterator {
             us: &'a mut impl Extend<B>,
         ) -> impl FnMut((), (A, B)) + 'a {
             move |(), (t, u)| {
-                ts.extend(Some(t));
-                us.extend(Some(u));
+                ts.extend_one(t);
+                us.extend_one(u);
             }
         }
 
         let mut ts: FromA = Default::default();
         let mut us: FromB = Default::default();
 
+        let (lower_bound, _) = self.size_hint();
+        if lower_bound > 0 {
+            ts.extend_reserve(lower_bound);
+            us.extend_reserve(lower_bound);
+        }
+
         self.fold((), extend(&mut ts, &mut us));
 
         (ts, us)

src/librustc_ast/token.rs

@@ -673,6 +673,62 @@ impl Token {
 
         Some(Token::new(kind, self.span.to(joint.span)))
     }
+
+    // See comments in `Nonterminal::to_tokenstream` for why we care about
+    // *probably* equal here rather than actual equality
+    crate fn probably_equal_for_proc_macro(&self, other: &Token) -> bool {
+        if mem::discriminant(&self.kind) != mem::discriminant(&other.kind) {
+            return false;
+        }
+        match (&self.kind, &other.kind) {
+            (&Eq, &Eq)
+            | (&Lt, &Lt)
+            | (&Le, &Le)
+            | (&EqEq, &EqEq)
+            | (&Ne, &Ne)
+            | (&Ge, &Ge)
+            | (&Gt, &Gt)
+            | (&AndAnd, &AndAnd)
+            | (&OrOr, &OrOr)
+            | (&Not, &Not)
+            | (&Tilde, &Tilde)
+            | (&At, &At)
+            | (&Dot, &Dot)
+            | (&DotDot, &DotDot)
+            | (&DotDotDot, &DotDotDot)
+            | (&DotDotEq, &DotDotEq)
+            | (&Comma, &Comma)
+            | (&Semi, &Semi)
+            | (&Colon, &Colon)
+            | (&ModSep, &ModSep)
+            | (&RArrow, &RArrow)
+            | (&LArrow, &LArrow)
+            | (&FatArrow, &FatArrow)
+            | (&Pound, &Pound)
+            | (&Dollar, &Dollar)
+            | (&Question, &Question)
+            | (&Whitespace, &Whitespace)
+            | (&Comment, &Comment)
+            | (&Eof, &Eof) => true,
+
+            (&BinOp(a), &BinOp(b)) | (&BinOpEq(a), &BinOpEq(b)) => a == b,
+
+            (&OpenDelim(a), &OpenDelim(b)) | (&CloseDelim(a), &CloseDelim(b)) => a == b,
+
+            (&DocComment(a), &DocComment(b)) | (&Shebang(a), &Shebang(b)) => a == b,
+
+            (&Literal(a), &Literal(b)) => a == b,
+
+            (&Lifetime(a), &Lifetime(b)) => a == b,
+            (&Ident(a, b), &Ident(c, d)) => {
+                b == d && (a == c || a == kw::DollarCrate || c == kw::DollarCrate)
+            }
+
+            (&Interpolated(_), &Interpolated(_)) => false,
+
+            _ => panic!("forgot to add a token?"),
+        }
+    }
 }
 
 impl PartialEq<TokenKind> for Token {

src/librustc_ast/tokenstream.rs

@@ -21,6 +21,8 @@ use rustc_macros::HashStable_Generic;
 use rustc_span::{Span, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 
+use log::debug;
+
 use std::{iter, mem};
 
 /// When the main rust parser encounters a syntax-extension invocation, it
@@ -66,6 +68,23 @@ impl TokenTree {
         }
     }
 
+    // See comments in `Nonterminal::to_tokenstream` for why we care about
+    // *probably* equal here rather than actual equality
+    //
+    // This is otherwise the same as `eq_unspanned`, only recursing with a
+    // different method.
+    pub fn probably_equal_for_proc_macro(&self, other: &TokenTree) -> bool {
+        match (self, other) {
+            (TokenTree::Token(token), TokenTree::Token(token2)) => {
+                token.probably_equal_for_proc_macro(token2)
+            }
+            (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => {
+                delim == delim2 && tts.probably_equal_for_proc_macro(&tts2)
+            }
+            _ => false,
+        }
+    }
+
     /// Retrieves the TokenTree's span.
     pub fn span(&self) -> Span {
         match self {
@@ -288,6 +307,112 @@ impl TokenStream {
         t1.next().is_none() && t2.next().is_none()
     }
 
+    // See comments in `Nonterminal::to_tokenstream` for why we care about
+    // *probably* equal here rather than actual equality
+    //
+    // This is otherwise the same as `eq_unspanned`, only recursing with a
+    // different method.
+    pub fn probably_equal_for_proc_macro(&self, other: &TokenStream) -> bool {
+        // When checking for `probably_eq`, we ignore certain tokens that aren't
+        // preserved in the AST. Because they are not preserved, the pretty
+        // printer arbitrarily adds or removes them when printing as token
+        // streams, making a comparison between a token stream generated from an
+        // AST and a token stream which was parsed into an AST more reliable.
+        fn semantic_tree(tree: &TokenTree) -> bool {
+            if let TokenTree::Token(token) = tree {
+                if let
+                    // The pretty printer tends to add trailing commas to
+                    // everything, and in particular, after struct fields.
+                    | token::Comma
+                    // The pretty printer emits `NoDelim` as whitespace.
+                    | token::OpenDelim(DelimToken::NoDelim)
+                    | token::CloseDelim(DelimToken::NoDelim)
+                    // The pretty printer collapses many semicolons into one.
+                    | token::Semi
+                    // The pretty printer collapses whitespace arbitrarily and can
+                    // introduce whitespace from `NoDelim`.
+                    | token::Whitespace
+                    // The pretty printer can turn `$crate` into `::crate_name`
+                    | token::ModSep = token.kind {
+                    return false;
+                }
+            }
+            true
+        }
+
+        // When comparing two `TokenStream`s, we ignore the `IsJoint` information.
+        //
+        // However, `rustc_parse::lexer::tokentrees::TokenStreamBuilder` will
+        // use `Token.glue` on adjacent tokens with the proper `IsJoint`.
+        // Since we are ignoreing `IsJoint`, a 'glued' token (e.g. `BinOp(Shr)`)
+        // and its 'split'/'unglued' compoenents (e.g. `Gt, Gt`) are equivalent
+        // when determining if two `TokenStream`s are 'probably equal'.
+        //
+        // Therefore, we use `break_two_token_op` to convert all tokens
+        // to the 'unglued' form (if it exists). This ensures that two
+        // `TokenStream`s which differ only in how their tokens are glued
+        // will be considered 'probably equal', which allows us to keep spans.
+        //
+        // This is important when the original `TokenStream` contained
+        // extra spaces (e.g. `f :: < Vec < _ > > ( ) ;'). These extra spaces
+        // will be omitted when we pretty-print, which can cause the original
+        // and reparsed `TokenStream`s to differ in the assignment of `IsJoint`,
+        // leading to some tokens being 'glued' together in one stream but not
+        // the other. See #68489 for more details.
+        fn break_tokens(tree: TokenTree) -> impl Iterator<Item = TokenTree> {
+            // In almost all cases, we should have either zero or one levels
+            // of 'unglueing'. However, in some unusual cases, we may need
+            // to iterate breaking tokens mutliple times. For example:
+            // '[BinOpEq(Shr)] => [Gt, Ge] -> [Gt, Gt, Eq]'
+            let mut token_trees: SmallVec<[_; 2]>;
+            if let TokenTree::Token(token) = &tree {
+                let mut out = SmallVec::<[_; 2]>::new();
+                out.push(token.clone());
+                // Iterate to fixpoint:
+                // * We start off with 'out' containing our initial token, and `temp` empty
+                // * If we are able to break any tokens in `out`, then `out` will have
+                //   at least one more element than 'temp', so we will try to break tokens
+                //   again.
+                // * If we cannot break any tokens in 'out', we are done
+                loop {
+                    let mut temp = SmallVec::<[_; 2]>::new();
+                    let mut changed = false;
+
+                    for token in out.into_iter() {
+                        if let Some((first, second)) = token.kind.break_two_token_op() {
+                            temp.push(Token::new(first, DUMMY_SP));
+                            temp.push(Token::new(second, DUMMY_SP));
+                            changed = true;
+                        } else {
+                            temp.push(token);
+                        }
+                    }
+                    out = temp;
+                    if !changed {
+                        break;
+                    }
+                }
+                token_trees = out.into_iter().map(|t| TokenTree::Token(t)).collect();
+                if token_trees.len() != 1 {
+                    debug!("break_tokens: broke {:?} to {:?}", tree, token_trees);
+                }
+            } else {
+                token_trees = SmallVec::new();
+                token_trees.push(tree);
+            }
+            token_trees.into_iter()
+        }
+
+        let mut t1 = self.trees().filter(semantic_tree).flat_map(break_tokens);
+        let mut t2 = other.trees().filter(semantic_tree).flat_map(break_tokens);
+        for (t1, t2) in t1.by_ref().zip(t2.by_ref()) {
+            if !t1.probably_equal_for_proc_macro(&t2) {
+                return false;
+            }
+        }
+        t1.next().is_none() && t2.next().is_none()
+    }
+
     pub fn map_enumerated<F: FnMut(usize, TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
         TokenStream(Lrc::new(
             self.0

src/librustc_ast_lowering/item.rs

@@ -1321,12 +1321,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                     .get_partial_res(bound_pred.bounded_ty.id)
                                     .map(|d| d.base_res())
                                 {
-                                    if let Some(node_id) =
-                                        self.resolver.definitions().as_local_node_id(def_id)
-                                    {
+                                    if let Some(def_id) = def_id.as_local() {
                                         for param in &generics.params {
                                             if let GenericParamKind::Type { .. } = param.kind {
-                                                if node_id == param.id {
+                                                if def_id
+                                                    == self
+                                                        .resolver
+                                                        .definitions()
+                                                        .local_def_id(param.id)
+                                                {
                                                     add_bounds
                                                         .entry(param.id)
                                                         .or_default()

src/librustc_ast_lowering/pat.rs

@@ -3,6 +3,7 @@ use super::{ImplTraitContext, LoweringContext, ParamMode};
 use rustc_ast::ast::*;
 use rustc_ast::ptr::P;
 use rustc_data_structures::stack::ensure_sufficient_stack;
+use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
 use rustc_span::symbol::Ident;
@@ -102,10 +103,36 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // Note that unlike for slice patterns,
             // where `xs @ ..` is a legal sub-slice pattern,
             // it is not a legal sub-tuple pattern.
-            if pat.is_rest() {
-                rest = Some((idx, pat.span));
-                break;
+            match pat.kind {
+                // Found a sub-tuple rest pattern
+                PatKind::Rest => {
+                    rest = Some((idx, pat.span));
+                    break;
+                }
+                // Found a sub-tuple pattern `$binding_mode $ident @ ..`.
+                // This is not allowed as a sub-tuple pattern
+                PatKind::Ident(ref _bm, ident, Some(ref sub)) if sub.is_rest() => {
+                    rest = Some((idx, pat.span));
+                    let sp = pat.span;
+                    self.diagnostic()
+                        .struct_span_err(
+                            sp,
+                            &format!("`{} @` is not allowed in a {}", ident.name, ctx),
+                        )
+                        .span_label(sp, "this is only allowed in slice patterns")
+                        .help("remove this and bind each tuple field independently")
+                        .span_suggestion_verbose(
+                            sp,
+                            &format!("if you don't need to use the contents of {}, discard the tuple's remaining fields", ident),
+                            "..".to_string(),
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                    break;
+                }
+                _ => {}
             }
+
             // It was not a sub-tuple pattern so lower it normally.
             elems.push(self.lower_pat(pat));
         }

src/librustc_data_structures/lib.rs

@@ -22,6 +22,7 @@
 #![feature(test)]
 #![feature(associated_type_bounds)]
 #![feature(thread_id_value)]
+#![feature(extend_one)]
 #![allow(rustc::default_hash_types)]
 
 #[macro_use]

src/librustc_data_structures/thin_vec.rs

@@ -53,6 +53,20 @@ impl<T> Extend<T> for ThinVec<T> {
             ThinVec(None) => *self = iter.into_iter().collect::<Vec<_>>().into(),
         }
     }
+
+    fn extend_one(&mut self, item: T) {
+        match *self {
+            ThinVec(Some(ref mut vec)) => vec.push(item),
+            ThinVec(None) => *self = vec![item].into(),
+        }
+    }
+
+    fn extend_reserve(&mut self, additional: usize) {
+        match *self {
+            ThinVec(Some(ref mut vec)) => vec.reserve(additional),
+            ThinVec(None) => *self = Vec::with_capacity(additional).into(),
+        }
+    }
 }
 
 impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ThinVec<T> {

src/librustc_hir/definitions.rs

@@ -332,17 +332,6 @@ impl Definitions {
         })
     }
 
-    #[inline]
-    pub fn as_local_node_id(&self, def_id: DefId) -> Option<ast::NodeId> {
-        if let Some(def_id) = def_id.as_local() {
-            let node_id = self.def_id_to_node_id[def_id];
-            if node_id != ast::DUMMY_NODE_ID {
-                return Some(node_id);
-            }
-        }
-        None
-    }
-
     #[inline]
     pub fn as_local_hir_id(&self, def_id: LocalDefId) -> hir::HirId {
         self.local_def_id_to_hir_id(def_id)

src/librustc_index/lib.rs

@@ -2,6 +2,7 @@
 #![feature(const_if_match)]
 #![feature(const_fn)]
 #![feature(const_panic)]
+#![feature(extend_one)]
 #![feature(unboxed_closures)]
 #![feature(test)]
 #![feature(fn_traits)]

src/librustc_index/vec.rs

@@ -736,6 +736,16 @@ impl<I: Idx, T> Extend<T> for IndexVec<I, T> {
     fn extend<J: IntoIterator<Item = T>>(&mut self, iter: J) {
         self.raw.extend(iter);
     }
+
+    #[inline]
+    fn extend_one(&mut self, item: T) {
+        self.raw.push(item);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.raw.reserve(additional);
+    }
 }
 
 impl<I: Idx, T> FromIterator<T> for IndexVec<I, T> {

src/librustc_infer/lib.rs

@@ -16,6 +16,7 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
+#![feature(extend_one)]
 #![feature(never_type)]
 #![feature(or_patterns)]
 #![feature(range_is_empty)]

src/librustc_infer/traits/util.rs

@@ -81,6 +81,14 @@ impl Extend<ty::Predicate<'tcx>> for PredicateSet<'tcx> {
             self.insert(pred);
         }
     }
+
+    fn extend_one(&mut self, pred: ty::Predicate<'tcx>) {
+        self.insert(pred);
+    }
+
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<ty::Predicate<'tcx>>::extend_reserve(&mut self.set, additional);
+    }
 }
 
 ///////////////////////////////////////////////////////////////////////////

src/librustc_middle/mir/interpret/error.rs

@@ -1,4 +1,4 @@
-use super::{AllocId, Pointer, RawConst, ScalarMaybeUninit};
+use super::{AllocId, Pointer, RawConst, Scalar};
 
 use crate::mir::interpret::ConstValue;
 use crate::ty::layout::LayoutError;
@@ -391,7 +391,7 @@ pub enum UndefinedBehaviorInfo<'tcx> {
     /// Using a non-character `u32` as character.
     InvalidChar(u32),
     /// An enum discriminant was set to a value which was outside the range of valid values.
-    InvalidDiscriminant(ScalarMaybeUninit),
+    InvalidDiscriminant(Scalar),
     /// Using a pointer-not-to-a-function as function pointer.
     InvalidFunctionPointer(Pointer),
     /// Using a string that is not valid UTF-8,

src/librustc_middle/mir/tcx.rs

@@ -5,7 +5,6 @@
 
 use crate::mir::*;
 use crate::ty::subst::Subst;
-use crate::ty::util::IntTypeExt;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_hir as hir;
 use rustc_target::abi::VariantIdx;
@@ -174,17 +173,7 @@ impl<'tcx> Rvalue<'tcx> {
                 tcx.intern_tup(&[ty, tcx.types.bool])
             }
             Rvalue::UnaryOp(UnOp::Not | UnOp::Neg, ref operand) => operand.ty(local_decls, tcx),
-            Rvalue::Discriminant(ref place) => {
-                let ty = place.ty(local_decls, tcx).ty;
-                match ty.kind {
-                    ty::Adt(adt_def, _) => adt_def.repr.discr_type().to_ty(tcx),
-                    ty::Generator(_, substs, _) => substs.as_generator().discr_ty(tcx),
-                    _ => {
-                        // This can only be `0`, for now, so `u8` will suffice.
-                        tcx.types.u8
-                    }
-                }
-            }
+            Rvalue::Discriminant(ref place) => place.ty(local_decls, tcx).ty.discriminant_ty(tcx),
             Rvalue::NullaryOp(NullOp::Box, t) => tcx.mk_box(t),
             Rvalue::NullaryOp(NullOp::SizeOf, _) => tcx.types.usize,
             Rvalue::Aggregate(ref ak, ref ops) => match **ak {

src/librustc_middle/ty/context.rs

@@ -2251,11 +2251,6 @@ impl<'tcx> TyCtxt<'tcx> {
         if self.features().never_type_fallback { self.types.never } else { self.types.unit }
     }
 
-    #[inline]
-    pub fn mk_bool(self) -> Ty<'tcx> {
-        self.mk_ty(Bool)
-    }
-
     #[inline]
     pub fn mk_fn_def(self, def_id: DefId, substs: SubstsRef<'tcx>) -> Ty<'tcx> {
         self.mk_ty(FnDef(def_id, substs))

src/librustc_middle/ty/mod.rs

@@ -2037,6 +2037,8 @@ impl ReprOptions {
         self.flags.contains(ReprFlags::HIDE_NICHE)
     }
 
+    /// Returns the discriminant type, given these `repr` options.
+    /// This must only be called on enums!
     pub fn discr_type(&self) -> attr::IntType {
         self.int.unwrap_or(attr::SignedInt(ast::IntTy::Isize))
     }
@@ -2269,6 +2271,7 @@ impl<'tcx> AdtDef {
 
     #[inline]
     pub fn eval_explicit_discr(&self, tcx: TyCtxt<'tcx>, expr_did: DefId) -> Option<Discr<'tcx>> {
+        assert!(self.is_enum());
         let param_env = tcx.param_env(expr_did);
         let repr_type = self.repr.discr_type();
         match tcx.const_eval_poly(expr_did) {
@@ -2305,6 +2308,7 @@ impl<'tcx> AdtDef {
         &'tcx self,
         tcx: TyCtxt<'tcx>,
     ) -> impl Iterator<Item = (VariantIdx, Discr<'tcx>)> + Captures<'tcx> {
+        assert!(self.is_enum());
         let repr_type = self.repr.discr_type();
         let initial = repr_type.initial_discriminant(tcx);
         let mut prev_discr = None::<Discr<'tcx>>;
@@ -2337,6 +2341,7 @@ impl<'tcx> AdtDef {
         tcx: TyCtxt<'tcx>,
         variant_index: VariantIdx,
     ) -> Discr<'tcx> {
+        assert!(self.is_enum());
         let (val, offset) = self.discriminant_def_for_variant(variant_index);
         let explicit_value = val
             .and_then(|expr_did| self.eval_explicit_discr(tcx, expr_did))

src/librustc_middle/ty/sty.rs

@@ -29,6 +29,7 @@ use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::marker::PhantomData;
 use std::ops::Range;
+use ty::util::IntTypeExt;
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
 #[derive(HashStable, TypeFoldable, Lift)]
@@ -2096,7 +2097,9 @@ impl<'tcx> TyS<'tcx> {
         variant_index: VariantIdx,
     ) -> Option<Discr<'tcx>> {
         match self.kind {
-            TyKind::Adt(adt, _) => Some(adt.discriminant_for_variant(tcx, variant_index)),
+            TyKind::Adt(adt, _) if adt.is_enum() => {
+                Some(adt.discriminant_for_variant(tcx, variant_index))
+            }
             TyKind::Generator(def_id, substs, _) => {
                 Some(substs.as_generator().discriminant_for_variant(def_id, tcx, variant_index))
             }
@@ -2104,6 +2107,18 @@ impl<'tcx> TyS<'tcx> {
         }
     }
 
+    /// Returns the type of the discriminant of this type.
+    pub fn discriminant_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        match self.kind {
+            ty::Adt(adt, _) if adt.is_enum() => adt.repr.discr_type().to_ty(tcx),
+            ty::Generator(_, substs, _) => substs.as_generator().discr_ty(tcx),
+            _ => {
+                // This can only be `0`, for now, so `u8` will suffice.
+                tcx.types.u8
+            }
+        }
+    }
+
     /// When we create a closure, we record its kind (i.e., what trait
     /// it implements) into its `ClosureSubsts` using a type
     /// parameter. This is kind of a phantom type, except that the

src/librustc_mir/interpret/intrinsics.rs

@@ -220,15 +220,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             sym::discriminant_value => {
                 let place = self.deref_operand(args[0])?;
                 let discr_val = self.read_discriminant(place.into())?.0;
-                let scalar = match dest.layout.ty.kind {
-                    ty::Int(_) => Scalar::from_int(
-                        self.sign_extend(discr_val, dest.layout) as i128,
-                        dest.layout.size,
-                    ),
-                    ty::Uint(_) => Scalar::from_uint(discr_val, dest.layout.size),
-                    _ => bug!("invalid `discriminant_value` return layout: {:?}", dest.layout),
-                };
-                self.write_scalar(scalar, dest)?;
+                self.write_scalar(discr_val, dest)?;
             }
             sym::unchecked_shl
             | sym::unchecked_shr

src/librustc_mir/interpret/operand.rs

@@ -7,15 +7,15 @@ use std::fmt::Write;
 use rustc_errors::ErrorReported;
 use rustc_hir::def::Namespace;
 use rustc_macros::HashStable;
-use rustc_middle::ty::layout::{IntegerExt, PrimitiveExt, TyAndLayout};
+use rustc_middle::ty::layout::{PrimitiveExt, TyAndLayout};
 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Printer};
 use rustc_middle::ty::Ty;
 use rustc_middle::{mir, ty};
-use rustc_target::abi::{Abi, DiscriminantKind, HasDataLayout, Integer, LayoutOf, Size};
+use rustc_target::abi::{Abi, DiscriminantKind, HasDataLayout, LayoutOf, Size};
 use rustc_target::abi::{VariantIdx, Variants};
 
 use super::{
-    from_known_layout, sign_extend, truncate, ConstValue, GlobalId, InterpCx, InterpResult,
+    from_known_layout, mir_assign_valid_types, ConstValue, GlobalId, InterpCx, InterpResult,
     MPlaceTy, Machine, MemPlace, Place, PlaceTy, Pointer, Scalar, ScalarMaybeUninit,
 };
 
@@ -469,6 +469,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             .try_fold(base_op, |op, elem| self.operand_projection(op, elem))?;
 
         trace!("eval_place_to_op: got {:?}", *op);
+        // Sanity-check the type we ended up with.
+        debug_assert!(mir_assign_valid_types(
+            *self.tcx,
+            self.layout_of(self.subst_from_current_frame_and_normalize_erasing_regions(
+                place.ty(&self.frame().body.local_decls, *self.tcx).ty
+            ))?,
+            op.layout,
+        ));
         Ok(op)
     }
 
@@ -576,98 +584,113 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Read discriminant, return the runtime value as well as the variant index.
     pub fn read_discriminant(
         &self,
-        rval: OpTy<'tcx, M::PointerTag>,
-    ) -> InterpResult<'tcx, (u128, VariantIdx)> {
-        trace!("read_discriminant_value {:#?}", rval.layout);
+        op: OpTy<'tcx, M::PointerTag>,
+    ) -> InterpResult<'tcx, (Scalar<M::PointerTag>, VariantIdx)> {
+        trace!("read_discriminant_value {:#?}", op.layout);
 
-        let (discr_layout, discr_kind, discr_index) = match rval.layout.variants {
+        // Get type and layout of the discriminant.
+        let discr_layout = self.layout_of(op.layout.ty.discriminant_ty(*self.tcx))?;
+        trace!("discriminant type: {:?}", discr_layout.ty);
+
+        // We use "discriminant" to refer to the value associated with a particular enum variant.
+        // This is not to be confused with its "variant index", which is just determining its position in the
+        // declared list of variants -- they can differ with explicitly assigned discriminants.
+        // We use "tag" to refer to how the discriminant is encoded in memory, which can be either
+        // straight-forward (`DiscriminantKind::Tag`) or with a niche (`DiscriminantKind::Niche`).
+        // Unfortunately, the rest of the compiler calls the latter "discriminant", too, which makes things
+        // rather confusing.
+        let (tag_scalar_layout, tag_kind, tag_index) = match op.layout.variants {
             Variants::Single { index } => {
-                let discr_val = rval
-                    .layout
-                    .ty
-                    .discriminant_for_variant(*self.tcx, index)
-                    .map_or(u128::from(index.as_u32()), |discr| discr.val);
-                return Ok((discr_val, index));
+                let discr = match op.layout.ty.discriminant_for_variant(*self.tcx, index) {
+                    Some(discr) => {
+                        // This type actually has discriminants.
+                        assert_eq!(discr.ty, discr_layout.ty);
+                        Scalar::from_uint(discr.val, discr_layout.size)
+                    }
+                    None => {
+                        // On a type without actual discriminants, variant is 0.
+                        assert_eq!(index.as_u32(), 0);
+                        Scalar::from_uint(index.as_u32(), discr_layout.size)
+                    }
+                };
+                return Ok((discr, index));
             }
-            Variants::Multiple { discr: ref discr_layout, ref discr_kind, discr_index, .. } => {
-                (discr_layout, discr_kind, discr_index)
+            Variants::Multiple { ref discr, ref discr_kind, discr_index, .. } => {
+                (discr, discr_kind, discr_index)
             }
         };
 
-        // read raw discriminant value
-        let discr_op = self.operand_field(rval, discr_index)?;
-        let discr_val = self.read_immediate(discr_op)?;
-        let raw_discr = discr_val.to_scalar_or_undef();
-        trace!("discr value: {:?}", raw_discr);
-        // post-process
-        Ok(match *discr_kind {
+        // There are *three* layouts that come into play here:
+        // - The discriminant has a type for typechecking. This is `discr_layout`, and is used for
+        //   the `Scalar` we return.
+        // - The tag (encoded discriminant) has layout `tag_layout`. This is always an integer type,
+        //   and used to interpret the value we read from the tag field.
+        //   For the return value, a cast to `discr_layout` is performed.
+        // - The field storing the tag has a layout, which is very similar to `tag_layout` but
+        //   may be a pointer. This is `tag_val.layout`; we just use it for sanity checks.
+
+        // Get layout for tag.
+        let tag_layout = self.layout_of(tag_scalar_layout.value.to_int_ty(*self.tcx))?;
+
+        // Read tag and sanity-check `tag_layout`.
+        let tag_val = self.read_immediate(self.operand_field(op, tag_index)?)?;
+        assert_eq!(tag_layout.size, tag_val.layout.size);
+        assert_eq!(tag_layout.abi.is_signed(), tag_val.layout.abi.is_signed());
+        let tag_val = tag_val.to_scalar()?;
+        trace!("tag value: {:?}", tag_val);
+
+        // Figure out which discriminant and variant this corresponds to.
+        Ok(match *tag_kind {
             DiscriminantKind::Tag => {
-                let bits_discr = raw_discr
-                    .not_undef()
-                    .and_then(|raw_discr| self.force_bits(raw_discr, discr_val.layout.size))
-                    .map_err(|_| err_ub!(InvalidDiscriminant(raw_discr.erase_tag())))?;
-                let real_discr = if discr_val.layout.abi.is_signed() {
-                    // going from layout tag type to typeck discriminant type
-                    // requires first sign extending with the discriminant layout
-                    let sexted = sign_extend(bits_discr, discr_val.layout.size);
-                    // and then zeroing with the typeck discriminant type
-                    let discr_ty = rval
-                        .layout
-                        .ty
-                        .ty_adt_def()
-                        .expect("tagged layout corresponds to adt")
-                        .repr
-                        .discr_type();
-                    let size = Integer::from_attr(self, discr_ty).size();
-                    truncate(sexted, size)
-                } else {
-                    bits_discr
-                };
-                // Make sure we catch invalid discriminants
-                let index = match rval.layout.ty.kind {
+                let tag_bits = self
+                    .force_bits(tag_val, tag_layout.size)
+                    .map_err(|_| err_ub!(InvalidDiscriminant(tag_val.erase_tag())))?;
+                // Cast bits from tag layout to discriminant layout.
+                let discr_val_cast = self.cast_from_scalar(tag_bits, tag_layout, discr_layout.ty);
+                let discr_bits = discr_val_cast.assert_bits(discr_layout.size);
+                // Convert discriminant to variant index, and catch invalid discriminants.
+                let index = match op.layout.ty.kind {
                     ty::Adt(adt, _) => {
-                        adt.discriminants(self.tcx.tcx).find(|(_, var)| var.val == real_discr)
+                        adt.discriminants(self.tcx.tcx).find(|(_, var)| var.val == discr_bits)
                     }
                     ty::Generator(def_id, substs, _) => {
                         let substs = substs.as_generator();
                         substs
                             .discriminants(def_id, self.tcx.tcx)
-                            .find(|(_, var)| var.val == real_discr)
+                            .find(|(_, var)| var.val == discr_bits)
                     }
                     _ => bug!("tagged layout for non-adt non-generator"),
                 }
-                .ok_or_else(|| err_ub!(InvalidDiscriminant(raw_discr.erase_tag())))?;
-                (real_discr, index.0)
+                .ok_or_else(|| err_ub!(InvalidDiscriminant(tag_val.erase_tag())))?;
+                // Return the cast value, and the index.
+                (discr_val_cast, index.0)
             }
             DiscriminantKind::Niche { dataful_variant, ref niche_variants, niche_start } => {
+                // Compute the variant this niche value/"tag" corresponds to. With niche layout,
+                // discriminant (encoded in niche/tag) and variant index are the same.
                 let variants_start = niche_variants.start().as_u32();
                 let variants_end = niche_variants.end().as_u32();
-                let raw_discr = raw_discr
-                    .not_undef()
-                    .map_err(|_| err_ub!(InvalidDiscriminant(ScalarMaybeUninit::Uninit)))?;
-                match raw_discr.to_bits_or_ptr(discr_val.layout.size, self) {
+                let variant = match tag_val.to_bits_or_ptr(tag_layout.size, self) {
                     Err(ptr) => {
                         // The niche must be just 0 (which an inbounds pointer value never is)
                         let ptr_valid = niche_start == 0
                             && variants_start == variants_end
                             && !self.memory.ptr_may_be_null(ptr);
                         if !ptr_valid {
-                            throw_ub!(InvalidDiscriminant(raw_discr.erase_tag().into()))
+                            throw_ub!(InvalidDiscriminant(tag_val.erase_tag()))
                         }
-                        (u128::from(dataful_variant.as_u32()), dataful_variant)
+                        dataful_variant
                     }
-                    Ok(raw_discr) => {
+                    Ok(tag_bits) => {
                         // We need to use machine arithmetic to get the relative variant idx:
-                        // variant_index_relative = discr_val - niche_start_val
-                        let discr_layout =
-                            self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
-                        let discr_val = ImmTy::from_uint(raw_discr, discr_layout);
-                        let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
+                        // variant_index_relative = tag_val - niche_start_val
+                        let tag_val = ImmTy::from_uint(tag_bits, tag_layout);
+                        let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);
                         let variant_index_relative_val =
-                            self.binary_op(mir::BinOp::Sub, discr_val, niche_start_val)?;
+                            self.binary_op(mir::BinOp::Sub, tag_val, niche_start_val)?;
                         let variant_index_relative = variant_index_relative_val
                             .to_scalar()?
-                            .assert_bits(discr_val.layout.size);
+                            .assert_bits(tag_val.layout.size);
                         // Check if this is in the range that indicates an actual discriminant.
                         if variant_index_relative <= u128::from(variants_end - variants_start) {
                             let variant_index_relative = u32::try_from(variant_index_relative)
@@ -676,7 +699,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                             let variant_index = variants_start
                                 .checked_add(variant_index_relative)
                                 .expect("overflow computing absolute variant idx");
-                            let variants_len = rval
+                            let variants_len = op
                                 .layout
                                 .ty
                                 .ty_adt_def()
@@ -684,12 +707,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                                 .variants
                                 .len();
                             assert!(usize::try_from(variant_index).unwrap() < variants_len);
-                            (u128::from(variant_index), VariantIdx::from_u32(variant_index))
+                            VariantIdx::from_u32(variant_index)
                         } else {
-                            (u128::from(dataful_variant.as_u32()), dataful_variant)
+                            dataful_variant
                         }
                     }
-                }
+                };
+                // Compute the size of the scalar we need to return.
+                // No need to cast, because the variant index directly serves as discriminant and is
+                // encoded in the tag.
+                (Scalar::from_uint(variant.as_u32(), discr_layout.size), variant)
             }
         })
     }

src/librustc_mir/interpret/place.rs

@@ -638,6 +638,14 @@ where
         }
 
         self.dump_place(place_ty.place);
+        // Sanity-check the type we ended up with.
+        debug_assert!(mir_assign_valid_types(
+            *self.tcx,
+            self.layout_of(self.subst_from_current_frame_and_normalize_erasing_regions(
+                place.ty(&self.frame().body.local_decls, *self.tcx).ty
+            ))?,
+            place_ty.layout,
+        ));
         Ok(place_ty)
     }
 

src/librustc_mir/interpret/step.rs

@@ -262,8 +262,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             Discriminant(place) => {
                 let op = self.eval_place_to_op(place, None)?;
                 let discr_val = self.read_discriminant(op)?.0;
-                let size = dest.layout.size;
-                self.write_scalar(Scalar::from_uint(discr_val, size), dest)?;
+                self.write_scalar(discr_val, dest)?;
             }
         }
 

src/librustc_parse/Cargo.toml

@@ -12,7 +12,6 @@ doctest = false
 [dependencies]
 bitflags = "1.0"
 log = "0.4"
-smallvec = { version = "1.0", features = ["union", "may_dangle"] }
 rustc_ast_pretty = { path = "../librustc_ast_pretty" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_feature = { path = "../librustc_feature" }

src/librustc_parse/lib.rs

@@ -7,18 +7,14 @@
 #![feature(or_patterns)]
 
 use rustc_ast::ast;
-use rustc_ast::token::{self, DelimToken, Nonterminal, Token, TokenKind};
-use rustc_ast::tokenstream::{self, IsJoint, TokenStream, TokenTree};
+use rustc_ast::token::{self, Nonterminal};
+use rustc_ast::tokenstream::{self, TokenStream, TokenTree};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Diagnostic, FatalError, Level, PResult};
 use rustc_session::parse::ParseSess;
-use rustc_span::symbol::kw;
-use rustc_span::{FileName, SourceFile, Span, DUMMY_SP};
+use rustc_span::{FileName, SourceFile, Span};
 
-use smallvec::SmallVec;
-
-use std::mem;
 use std::path::Path;
 use std::str;
 
@@ -310,7 +306,7 @@ pub fn nt_to_tokenstream(nt: &Nonterminal, sess: &ParseSess, span: Span) -> Toke
     // modifications, including adding/removing typically non-semantic
     // tokens such as extra braces and commas, don't happen.
     if let Some(tokens) = tokens {
-        if tokenstream_probably_equal_for_proc_macro(&tokens, &tokens_for_real, sess) {
+        if tokens.probably_equal_for_proc_macro(&tokens_for_real) {
             return tokens;
         }
         info!(
@@ -385,203 +381,3 @@ fn prepend_attrs(
     builder.push(tokens.clone());
     Some(builder.build())
 }
-
-// See comments in `Nonterminal::to_tokenstream` for why we care about
-// *probably* equal here rather than actual equality
-//
-// This is otherwise the same as `eq_unspanned`, only recursing with a
-// different method.
-pub fn tokenstream_probably_equal_for_proc_macro(
-    first: &TokenStream,
-    other: &TokenStream,
-    sess: &ParseSess,
-) -> bool {
-    // When checking for `probably_eq`, we ignore certain tokens that aren't
-    // preserved in the AST. Because they are not preserved, the pretty
-    // printer arbitrarily adds or removes them when printing as token
-    // streams, making a comparison between a token stream generated from an
-    // AST and a token stream which was parsed into an AST more reliable.
-    fn semantic_tree(tree: &TokenTree) -> bool {
-        if let TokenTree::Token(token) = tree {
-            if let
-                // The pretty printer tends to add trailing commas to
-                // everything, and in particular, after struct fields.
-                | token::Comma
-                // The pretty printer emits `NoDelim` as whitespace.
-                | token::OpenDelim(DelimToken::NoDelim)
-                | token::CloseDelim(DelimToken::NoDelim)
-                // The pretty printer collapses many semicolons into one.
-                | token::Semi
-                // The pretty printer collapses whitespace arbitrarily and can
-                // introduce whitespace from `NoDelim`.
-                | token::Whitespace
-                // The pretty printer can turn `$crate` into `::crate_name`
-                | token::ModSep = token.kind {
-                return false;
-            }
-        }
-        true
-    }
-
-    // When comparing two `TokenStream`s, we ignore the `IsJoint` information.
-    //
-    // However, `rustc_parse::lexer::tokentrees::TokenStreamBuilder` will
-    // use `Token.glue` on adjacent tokens with the proper `IsJoint`.
-    // Since we are ignoreing `IsJoint`, a 'glued' token (e.g. `BinOp(Shr)`)
-    // and its 'split'/'unglued' compoenents (e.g. `Gt, Gt`) are equivalent
-    // when determining if two `TokenStream`s are 'probably equal'.
-    //
-    // Therefore, we use `break_two_token_op` to convert all tokens
-    // to the 'unglued' form (if it exists). This ensures that two
-    // `TokenStream`s which differ only in how their tokens are glued
-    // will be considered 'probably equal', which allows us to keep spans.
-    //
-    // This is important when the original `TokenStream` contained
-    // extra spaces (e.g. `f :: < Vec < _ > > ( ) ;'). These extra spaces
-    // will be omitted when we pretty-print, which can cause the original
-    // and reparsed `TokenStream`s to differ in the assignment of `IsJoint`,
-    // leading to some tokens being 'glued' together in one stream but not
-    // the other. See #68489 for more details.
-    fn break_tokens(tree: TokenTree) -> impl Iterator<Item = TokenTree> {
-        // In almost all cases, we should have either zero or one levels
-        // of 'unglueing'. However, in some unusual cases, we may need
-        // to iterate breaking tokens mutliple times. For example:
-        // '[BinOpEq(Shr)] => [Gt, Ge] -> [Gt, Gt, Eq]'
-        let mut token_trees: SmallVec<[_; 2]>;
-        if let TokenTree::Token(token) = &tree {
-            let mut out = SmallVec::<[_; 2]>::new();
-            out.push(token.clone());
-            // Iterate to fixpoint:
-            // * We start off with 'out' containing our initial token, and `temp` empty
-            // * If we are able to break any tokens in `out`, then `out` will have
-            //   at least one more element than 'temp', so we will try to break tokens
-            //   again.
-            // * If we cannot break any tokens in 'out', we are done
-            loop {
-                let mut temp = SmallVec::<[_; 2]>::new();
-                let mut changed = false;
-
-                for token in out.into_iter() {
-                    if let Some((first, second)) = token.kind.break_two_token_op() {
-                        temp.push(Token::new(first, DUMMY_SP));
-                        temp.push(Token::new(second, DUMMY_SP));
-                        changed = true;
-                    } else {
-                        temp.push(token);
-                    }
-                }
-                out = temp;
-                if !changed {
-                    break;
-                }
-            }
-            token_trees = out.into_iter().map(|t| TokenTree::Token(t)).collect();
-            if token_trees.len() != 1 {
-                debug!("break_tokens: broke {:?} to {:?}", tree, token_trees);
-            }
-        } else {
-            token_trees = SmallVec::new();
-            token_trees.push(tree);
-        }
-        token_trees.into_iter()
-    }
-
-    let expand_nt = |tree: TokenTree| {
-        if let TokenTree::Token(Token { kind: TokenKind::Interpolated(nt), span }) = &tree {
-            nt_to_tokenstream(nt, sess, *span).into_trees()
-        } else {
-            TokenStream::new(vec![(tree, IsJoint::NonJoint)]).into_trees()
-        }
-    };
-
-    // Break tokens after we expand any nonterminals, so that we break tokens
-    // that are produced as a result of nonterminal expansion.
-    let mut t1 = first.trees().filter(semantic_tree).flat_map(expand_nt).flat_map(break_tokens);
-    let mut t2 = other.trees().filter(semantic_tree).flat_map(expand_nt).flat_map(break_tokens);
-    for (t1, t2) in t1.by_ref().zip(t2.by_ref()) {
-        if !tokentree_probably_equal_for_proc_macro(&t1, &t2, sess) {
-            return false;
-        }
-    }
-    t1.next().is_none() && t2.next().is_none()
-}
-
-// See comments in `Nonterminal::to_tokenstream` for why we care about
-// *probably* equal here rather than actual equality
-crate fn token_probably_equal_for_proc_macro(first: &Token, other: &Token) -> bool {
-    use TokenKind::*;
-
-    if mem::discriminant(&first.kind) != mem::discriminant(&other.kind) {
-        return false;
-    }
-    match (&first.kind, &other.kind) {
-        (&Eq, &Eq)
-        | (&Lt, &Lt)
-        | (&Le, &Le)
-        | (&EqEq, &EqEq)
-        | (&Ne, &Ne)
-        | (&Ge, &Ge)
-        | (&Gt, &Gt)
-        | (&AndAnd, &AndAnd)
-        | (&OrOr, &OrOr)
-        | (&Not, &Not)
-        | (&Tilde, &Tilde)
-        | (&At, &At)
-        | (&Dot, &Dot)
-        | (&DotDot, &DotDot)
-        | (&DotDotDot, &DotDotDot)
-        | (&DotDotEq, &DotDotEq)
-        | (&Comma, &Comma)
-        | (&Semi, &Semi)
-        | (&Colon, &Colon)
-        | (&ModSep, &ModSep)
-        | (&RArrow, &RArrow)
-        | (&LArrow, &LArrow)
-        | (&FatArrow, &FatArrow)
-        | (&Pound, &Pound)
-        | (&Dollar, &Dollar)
-        | (&Question, &Question)
-        | (&Whitespace, &Whitespace)
-        | (&Comment, &Comment)
-        | (&Eof, &Eof) => true,
-
-        (&BinOp(a), &BinOp(b)) | (&BinOpEq(a), &BinOpEq(b)) => a == b,
-
-        (&OpenDelim(a), &OpenDelim(b)) | (&CloseDelim(a), &CloseDelim(b)) => a == b,
-
-        (&DocComment(a), &DocComment(b)) | (&Shebang(a), &Shebang(b)) => a == b,
-
-        (&Literal(a), &Literal(b)) => a == b,
-
-        (&Lifetime(a), &Lifetime(b)) => a == b,
-        (&Ident(a, b), &Ident(c, d)) => {
-            b == d && (a == c || a == kw::DollarCrate || c == kw::DollarCrate)
-        }
-
-        // Expanded by `tokenstream_probably_equal_for_proc_macro`
-        (&Interpolated(_), &Interpolated(_)) => unreachable!(),
-
-        _ => panic!("forgot to add a token?"),
-    }
-}
-
-// See comments in `Nonterminal::to_tokenstream` for why we care about
-// *probably* equal here rather than actual equality
-//
-// This is otherwise the same as `eq_unspanned`, only recursing with a
-// different method.
-pub fn tokentree_probably_equal_for_proc_macro(
-    first: &TokenTree,
-    other: &TokenTree,
-    sess: &ParseSess,
-) -> bool {
-    match (first, other) {
-        (TokenTree::Token(token), TokenTree::Token(token2)) => {
-            token_probably_equal_for_proc_macro(token, token2)
-        }
-        (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => {
-            delim == delim2 && tokenstream_probably_equal_for_proc_macro(&tts, &tts2, sess)
-        }
-        _ => false,
-    }
-}

src/librustc_resolve/build_reduced_graph.rs

@@ -25,7 +25,7 @@ use rustc_errors::{struct_span_err, Applicability};
 use rustc_expand::base::SyntaxExtension;
 use rustc_expand::expand::AstFragment;
 use rustc_hir::def::{self, *};
-use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX};
 use rustc_metadata::creader::LoadedMacro;
 use rustc_middle::bug;
 use rustc_middle::hir::exports::Export;
@@ -1150,15 +1150,22 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
     // Mark the given macro as unused unless its name starts with `_`.
     // Macro uses will remove items from this set, and the remaining
     // items will be reported as `unused_macros`.
-    fn insert_unused_macro(&mut self, ident: Ident, node_id: NodeId, span: Span) {
+    fn insert_unused_macro(
+        &mut self,
+        ident: Ident,
+        def_id: LocalDefId,
+        node_id: NodeId,
+        span: Span,
+    ) {
         if !ident.as_str().starts_with('_') {
-            self.r.unused_macros.insert(node_id, span);
+            self.r.unused_macros.insert(def_id, (node_id, span));
         }
     }
 
     fn define_macro(&mut self, item: &ast::Item) -> MacroRulesScope<'a> {
         let parent_scope = self.parent_scope;
         let expansion = parent_scope.expansion;
+        let def_id = self.r.definitions.local_def_id(item.id);
         let (ext, ident, span, macro_rules) = match &item.kind {
             ItemKind::MacroDef(def) => {
                 let ext = Lrc::new(self.r.compile_macro(item, self.r.session.edition()));
@@ -1166,7 +1173,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             }
             ItemKind::Fn(..) => match Self::proc_macro_stub(item) {
                 Some((macro_kind, ident, span)) => {
-                    self.r.proc_macro_stubs.insert(item.id);
+                    self.r.proc_macro_stubs.insert(def_id);
                     (self.r.dummy_ext(macro_kind), ident, span, false)
                 }
                 None => return parent_scope.macro_rules,
@@ -1174,7 +1181,6 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             _ => unreachable!(),
         };
 
-        let def_id = self.r.definitions.local_def_id(item.id);
         let res = Res::Def(DefKind::Macro(ext.macro_kind()), def_id.to_def_id());
         self.r.macro_map.insert(def_id.to_def_id(), ext);
         self.r.local_macro_def_scopes.insert(def_id, parent_scope.module);
@@ -1196,7 +1202,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 self.r.define(module, ident, MacroNS, (res, vis, span, expansion, IsMacroExport));
             } else {
                 self.r.check_reserved_macro_name(ident, res);
-                self.insert_unused_macro(ident, item.id, span);
+                self.insert_unused_macro(ident, def_id, item.id, span);
             }
             MacroRulesScope::Binding(self.r.arenas.alloc_macro_rules_binding(MacroRulesBinding {
                 parent_macro_rules_scope: parent_scope.macro_rules,
@@ -1214,7 +1220,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 _ => self.resolve_visibility(&item.vis),
             };
             if vis != ty::Visibility::Public {
-                self.insert_unused_macro(ident, item.id, span);
+                self.insert_unused_macro(ident, def_id, item.id, span);
             }
             self.r.define(module, ident, MacroNS, (res, vis, span, expansion));
             self.parent_scope.macro_rules

src/librustc_resolve/late.rs

@@ -1621,11 +1621,10 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         let report_errors = |this: &mut Self, res: Option<Res>| {
             let (err, candidates) = this.smart_resolve_report_errors(path, span, source, res);
             let def_id = this.parent_scope.module.normal_ancestor_id;
-            let node_id = this.r.definitions.as_local_node_id(def_id).unwrap();
             let better = res.is_some();
             let suggestion =
                 if res.is_none() { this.report_missing_type_error(path) } else { None };
-            this.r.use_injections.push(UseError { err, candidates, node_id, better, suggestion });
+            this.r.use_injections.push(UseError { err, candidates, def_id, better, suggestion });
             PartialRes::new(Res::Err)
         };
 

src/librustc_resolve/lib.rs

@@ -23,7 +23,7 @@ use rustc_ast::ast::{self, FloatTy, IntTy, NodeId, UintTy};
 use rustc_ast::ast::{Crate, CRATE_NODE_ID};
 use rustc_ast::ast::{ItemKind, Path};
 use rustc_ast::attr;
-use rustc_ast::node_id::{NodeMap, NodeSet};
+use rustc_ast::node_id::NodeMap;
 use rustc_ast::unwrap_or;
 use rustc_ast::visit::{self, Visitor};
 use rustc_ast_pretty::pprust;
@@ -253,21 +253,31 @@ impl<'a> From<&'a ast::PathSegment> for Segment {
     }
 }
 
-struct UsePlacementFinder {
-    target_module: NodeId,
+struct UsePlacementFinder<'d> {
+    definitions: &'d Definitions,
+    target_module: LocalDefId,
     span: Option<Span>,
     found_use: bool,
 }
 
-impl UsePlacementFinder {
-    fn check(krate: &Crate, target_module: NodeId) -> (Option<Span>, bool) {
-        let mut finder = UsePlacementFinder { target_module, span: None, found_use: false };
-        visit::walk_crate(&mut finder, krate);
-        (finder.span, finder.found_use)
+impl<'d> UsePlacementFinder<'d> {
+    fn check(
+        definitions: &'d Definitions,
+        krate: &Crate,
+        target_module: DefId,
+    ) -> (Option<Span>, bool) {
+        if let Some(target_module) = target_module.as_local() {
+            let mut finder =
+                UsePlacementFinder { definitions, target_module, span: None, found_use: false };
+            visit::walk_crate(&mut finder, krate);
+            (finder.span, finder.found_use)
+        } else {
+            (None, false)
+        }
     }
 }
 
-impl<'tcx> Visitor<'tcx> for UsePlacementFinder {
+impl<'tcx, 'd> Visitor<'tcx> for UsePlacementFinder<'d> {
     fn visit_mod(
         &mut self,
         module: &'tcx ast::Mod,
@@ -278,7 +288,7 @@ impl<'tcx> Visitor<'tcx> for UsePlacementFinder {
         if self.span.is_some() {
             return;
         }
-        if node_id != self.target_module {
+        if self.definitions.local_def_id(node_id) != self.target_module {
             visit::walk_mod(self, module);
             return;
         }
@@ -611,7 +621,7 @@ struct UseError<'a> {
     /// Attach `use` statements for these candidates.
     candidates: Vec<ImportSuggestion>,
     /// The `NodeId` of the module to place the use-statements in.
-    node_id: NodeId,
+    def_id: DefId,
     /// Whether the diagnostic should state that it's "better".
     better: bool,
     /// Extra free form suggestion. Currently used to suggest new type parameter.
@@ -926,8 +936,8 @@ pub struct Resolver<'a> {
     non_macro_attrs: [Lrc<SyntaxExtension>; 2],
     local_macro_def_scopes: FxHashMap<LocalDefId, Module<'a>>,
     ast_transform_scopes: FxHashMap<ExpnId, Module<'a>>,
-    unused_macros: NodeMap<Span>,
-    proc_macro_stubs: NodeSet,
+    unused_macros: FxHashMap<LocalDefId, (NodeId, Span)>,
+    proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
     single_segment_macro_resolutions:
         Vec<(Ident, MacroKind, ParentScope<'a>, Option<&'a NameBinding<'a>>)>,
@@ -2567,10 +2577,10 @@ impl<'a> Resolver<'a> {
     }
 
     fn report_with_use_injections(&mut self, krate: &Crate) {
-        for UseError { mut err, candidates, node_id, better, suggestion } in
+        for UseError { mut err, candidates, def_id, better, suggestion } in
             self.use_injections.drain(..)
         {
-            let (span, found_use) = UsePlacementFinder::check(krate, node_id);
+            let (span, found_use) = UsePlacementFinder::check(&self.definitions, krate, def_id);
             if !candidates.is_empty() {
                 diagnostics::show_candidates(&mut err, span, &candidates, better, found_use);
             } else if let Some((span, msg, sugg, appl)) = suggestion {

src/librustc_resolve/macros.rs

@@ -333,7 +333,7 @@ impl<'a> base::Resolver for Resolver<'a> {
     }
 
     fn check_unused_macros(&mut self) {
-        for (&node_id, &span) in self.unused_macros.iter() {
+        for (_, &(node_id, span)) in self.unused_macros.iter() {
             self.lint_buffer.buffer_lint(UNUSED_MACROS, node_id, span, "unused macro definition");
         }
     }
@@ -416,9 +416,9 @@ impl<'a> Resolver<'a> {
 
         match res {
             Res::Def(DefKind::Macro(_), def_id) => {
-                if let Some(node_id) = self.definitions.as_local_node_id(def_id) {
-                    self.unused_macros.remove(&node_id);
-                    if self.proc_macro_stubs.contains(&node_id) {
+                if let Some(def_id) = def_id.as_local() {
+                    self.unused_macros.remove(&def_id);
+                    if self.proc_macro_stubs.contains(&def_id) {
                         self.session.span_err(
                             path.span,
                             "can't use a procedural macro from the same crate that defines it",

src/librustc_trait_selection/traits/select.rs

@@ -1040,17 +1040,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         stack: &TraitObligationStack<'o, 'tcx>,
     ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
-        if stack.obligation.predicate.references_error() {
-            // If we encounter a `Error`, we generally prefer the
-            // most "optimistic" result in response -- that is, the
-            // one least likely to report downstream errors. But
-            // because this routine is shared by coherence and by
-            // trait selection, there isn't an obvious "right" choice
-            // here in that respect, so we opt to just return
-            // ambiguity and let the upstream clients sort it out.
-            return Ok(None);
-        }
-
         if let Some(conflict) = self.is_knowable(stack) {
             debug!("coherence stage: not knowable");
             if self.intercrate_ambiguity_causes.is_some() {

src/librustc_typeck/check/op.rs

@@ -121,9 +121,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let tcx = self.tcx;
         match BinOpCategory::from(op) {
             BinOpCategory::Shortcircuit => {
-                self.demand_suptype(*lhs_span, tcx.mk_bool(), lhs_ty);
-                self.demand_suptype(*rhs_span, tcx.mk_bool(), rhs_ty);
-                tcx.mk_bool()
+                self.demand_suptype(*lhs_span, tcx.types.bool, lhs_ty);
+                self.demand_suptype(*rhs_span, tcx.types.bool, rhs_ty);
+                tcx.types.bool
             }
 
             BinOpCategory::Shift => {
@@ -140,7 +140,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             BinOpCategory::Comparison => {
                 // both LHS and RHS and result will have the same type
                 self.demand_suptype(*rhs_span, lhs_ty, rhs_ty);
-                tcx.mk_bool()
+                tcx.types.bool
             }
         }
     }

src/libstd/collections/hash/map.rs

@@ -2426,6 +2426,24 @@ where
     fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
         self.base.extend(iter)
     }
+
+    #[inline]
+    fn extend_one(&mut self, (k, v): (K, V)) {
+        self.base.insert(k, v);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        // self.base.extend_reserve(additional);
+        // FIXME: hashbrown should implement this method.
+        // But until then, use the same reservation logic:
+
+        // Reserve the entire hint lower bound if the map is empty.
+        // Otherwise reserve half the hint (rounded up), so the map
+        // will only resize twice in the worst case.
+        let reserve = if self.is_empty() { additional } else { (additional + 1) / 2 };
+        self.base.reserve(reserve);
+    }
 }
 
 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
@@ -2439,6 +2457,16 @@ where
     fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
         self.base.extend(iter)
     }
+
+    #[inline]
+    fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
+        self.base.insert(k, v);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<(K, V)>::extend_reserve(self, additional)
+    }
 }
 
 /// `RandomState` is the default state for [`HashMap`] types.

src/libstd/collections/hash/set.rs

@@ -970,6 +970,16 @@ where
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
         self.map.extend(iter.into_iter().map(|k| (k, ())));
     }
+
+    #[inline]
+    fn extend_one(&mut self, item: T) {
+        self.map.insert(item, ());
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        self.map.extend_reserve(additional);
+    }
 }
 
 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
@@ -982,6 +992,16 @@ where
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
+
+    #[inline]
+    fn extend_one(&mut self, &item: &'a T) {
+        self.map.insert(item, ());
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<T>::extend_reserve(self, additional)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/libstd/lib.rs

@@ -263,6 +263,7 @@
 #![feature(duration_constants)]
 #![feature(exact_size_is_empty)]
 #![feature(exhaustive_patterns)]
+#![feature(extend_one)]
 #![feature(external_doc)]
 #![feature(fn_traits)]
 #![feature(format_args_nl)]

src/libstd/path.rs

@@ -1534,6 +1534,11 @@ impl<P: AsRef<Path>> iter::Extend<P> for PathBuf {
     fn extend<I: IntoIterator<Item = P>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |p| self.push(p.as_ref()));
     }
+
+    #[inline]
+    fn extend_one(&mut self, p: P) {
+        self.push(p.as_ref());
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/libstd/sys_common/wtf8.rs

@@ -386,6 +386,17 @@ impl Extend<CodePoint> for Wtf8Buf {
         self.bytes.reserve(low);
         iterator.for_each(move |code_point| self.push(code_point));
     }
+
+    #[inline]
+    fn extend_one(&mut self, code_point: CodePoint) {
+        self.push(code_point);
+    }
+
+    #[inline]
+    fn extend_reserve(&mut self, additional: usize) {
+        // Lower bound of one byte per code point (ASCII only)
+        self.bytes.reserve(additional);
+    }
 }
 
 /// A borrowed slice of well-formed WTF-8 data.

src/test/run-make-fulldeps/long-linker-command-lines/foo.rs

@@ -90,7 +90,7 @@ fn main() {
         }
 
         let linker_args = read_linker_args(&ok);
-        for mut arg in linker_args.split('S') {
+        for arg in linker_args.split('S') {
             expected_libs.remove(arg);
         }
 

src/test/ui/async-await/issue-72590-type-error-sized.rs

@@ -0,0 +1,22 @@
+// Regression test for issue #72590
+// Tests that we don't emit a spurious "size cannot be statically determined" error
+// edition:2018
+
+struct Foo {
+    foo: Nonexistent, //~ ERROR cannot find
+    other: str
+}
+
+struct Bar {
+    test: Missing //~ ERROR cannot find
+}
+
+impl Foo {
+    async fn frob(self) {} //~ ERROR the size
+}
+
+impl Bar {
+    async fn myfn(self) {}
+}
+
+fn main() {}

src/test/ui/async-await/issue-72590-type-error-sized.stderr

@@ -0,0 +1,28 @@
+error[E0412]: cannot find type `Nonexistent` in this scope
+  --> $DIR/issue-72590-type-error-sized.rs:6:10
+   |
+LL |     foo: Nonexistent,
+   |          ^^^^^^^^^^^ not found in this scope
+
+error[E0412]: cannot find type `Missing` in this scope
+  --> $DIR/issue-72590-type-error-sized.rs:11:11
+   |
+LL |     test: Missing
+   |           ^^^^^^^ not found in this scope
+
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/issue-72590-type-error-sized.rs:15:19
+   |
+LL |     async fn frob(self) {}
+   |                   ^^^^ doesn't have a size known at compile-time
+   |
+   = help: within `Foo`, the trait `std::marker::Sized` is not implemented for `str`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: required because it appears within the type `Foo`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0412.
+For more information about an error, try `rustc --explain E0277`.

src/test/ui/issues/issue-72574-1.rs

@@ -0,0 +1,8 @@
+fn main() {
+    let x = (1, 2, 3);
+    match x {
+        (_a, _x @ ..) => {}
+        _ => {}
+    }
+}
+//~^^^^ ERROR `_x @` is not allowed in a tuple

src/test/ui/issues/issue-72574-1.stderr

@@ -0,0 +1,14 @@
+error: `_x @` is not allowed in a tuple
+  --> $DIR/issue-72574-1.rs:4:14
+   |
+LL |         (_a, _x @ ..) => {}
+   |              ^^^^^^^ this is only allowed in slice patterns
+   |
+   = help: remove this and bind each tuple field independently
+help: if you don't need to use the contents of _x, discard the tuple's remaining fields
+   |
+LL |         (_a, ..) => {}
+   |              ^^
+
+error: aborting due to previous error
+

src/test/ui/issues/issue-72574-2.rs

@@ -0,0 +1,10 @@
+struct Binder(i32, i32, i32);
+
+fn main() {
+    let x = Binder(1, 2, 3);
+    match x {
+        Binder(_a, _x @ ..) => {}
+        _ => {}
+    }
+}
+//~^^^^ ERROR `_x @` is not allowed in a tuple struct

src/test/ui/issues/issue-72574-2.stderr

@@ -0,0 +1,14 @@
+error: `_x @` is not allowed in a tuple struct
+  --> $DIR/issue-72574-2.rs:6:20
+   |
+LL |         Binder(_a, _x @ ..) => {}
+   |                    ^^^^^^^ this is only allowed in slice patterns
+   |
+   = help: remove this and bind each tuple field independently
+help: if you don't need to use the contents of _x, discard the tuple's remaining fields
+   |
+LL |         Binder(_a, ..) => {}
+   |                    ^^
+
+error: aborting due to previous error
+

src/test/ui/proc-macro/macro-rules-capture.rs

@@ -1,18 +0,0 @@
-// aux-build: test-macros.rs
-
-extern crate test_macros;
-use test_macros::recollect_attr;
-
-macro_rules! reemit {
-    ($name:ident => $($token:expr)*) => {
-
-        #[recollect_attr]
-        pub fn $name() {
-            $($token)*;
-        }
-    }
-}
-
-reemit! { foo => 45u32.into() } //~ ERROR type annotations
-
-fn main() {}

src/test/ui/proc-macro/macro-rules-capture.stderr

@@ -1,12 +0,0 @@
-error[E0282]: type annotations needed
-  --> $DIR/macro-rules-capture.rs:16:24
-   |
-LL | reemit! { foo => 45u32.into() }
-   |                  ------^^^^--
-   |                  |     |
-   |                  |     cannot infer type for type parameter `T` declared on the trait `Into`
-   |                  this method call resolves to `T`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0282`.

src/test/ui/unused-crate-deps/test-use-ok.rs

@@ -0,0 +1,15 @@
+// Test-only use OK
+
+// edition:2018
+// check-pass
+// aux-crate:bar=bar.rs
+// compile-flags:--test
+
+#![deny(unused_crate_dependencies)]
+
+fn main() {}
+
+#[test]
+fn test_bar() {
+    assert_eq!(bar::BAR, "bar");
+}