Auto merge of #70931 - Dylan-DPC:rollup-f8orcao, r=Dylan-DPC

Rollup of 9 pull requests

Successful merges:

 - #70789 (remove false positives of unused_braces)
 - #70847 (ci: move /var/lib/docker to /mnt on GHA)
 - #70850 (BTreeMap first last proposal tweaks)
 - #70876 (Use a `SmallVec` for `Cache::predecessors`.)
 - #70883 (Clean up E0507 explanation)
 - #70892 (wf: refactor `compute_trait_ref`)
 - #70914 (Corrects a typo in rustdoc documentation.)
 - #70915 (Remove unnecessary TypeFlags::NOMINAL_FLAGS)
 - #70927 (Clean up E0510 explanation)

Failed merges:

r? @ghost

src/ci/scripts/symlink-build-dir.sh

@@ -24,4 +24,10 @@ elif isLinux && isGitHubActions; then
     mv "${current_dir}" /mnt/more-space/workspace
     ln -s /mnt/more-space/workspace "${current_dir}"
     cd "${current_dir}"
+
+    # Move the Docker data directory to /mnt
+    sudo systemctl stop docker.service
+    sudo mv /var/lib/docker /mnt/docker
+    sudo ln -s /mnt/docker /var/lib/docker
+    sudo systemctl start docker.service
 fi

src/doc/rustdoc/src/documentation-tests.md

@@ -352,9 +352,9 @@ are added.
 /// ```
 ```
 
-`edition2018` tells `rustdoc` that the code sample should be compiled the 2018
-edition of Rust. Similarly, you can specify `edition2015` to compile the code
-with the 2015 edition.
+`edition2018` tells `rustdoc` that the code sample should be compiled using
+the 2018 edition of Rust. Similarly, you can specify `edition2015` to compile
+the code with the 2015 edition.
 
 ## Syntax reference
 

src/liballoc/collections/btree/map.rs

@@ -653,11 +653,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.first_key_value(), Some((&1, &"b")));
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn first_key_value<T: ?Sized>(&self) -> Option<(&K, &V)>
-    where
-        T: Ord,
-        K: Borrow<T>,
-    {
+    pub fn first_key_value(&self) -> Option<(&K, &V)> {
         let front = self.root.as_ref()?.as_ref().first_leaf_edge();
         front.right_kv().ok().map(Handle::into_kv)
     }
@@ -667,36 +663,54 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
-    /// Contrived way to `clear` a map:
-    ///
     /// ```
     /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
     /// map.insert(1, "a");
     /// map.insert(2, "b");
-    /// while let Some(entry) = map.first_entry() {
-    ///     let (key, val) = entry.remove_entry();
-    ///     assert!(!map.contains_key(&key));
+    /// if let Some(mut entry) = map.first_entry() {
+    ///     if *entry.key() > 0 {
+    ///         entry.insert("first");
+    ///     }
     /// }
+    /// assert_eq!(*map.get(&1).unwrap(), "first");
+    /// assert_eq!(*map.get(&2).unwrap(), "b");
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn first_entry<T: ?Sized>(&mut self) -> Option<OccupiedEntry<'_, K, V>>
-    where
-        T: Ord,
-        K: Borrow<T>,
-    {
+    pub fn first_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>> {
         let front = self.root.as_mut()?.as_mut().first_leaf_edge();
-        if let Ok(kv) = front.right_kv() {
-            Some(OccupiedEntry {
-                handle: kv.forget_node_type(),
-                length: &mut self.length,
-                _marker: PhantomData,
-            })
-        } else {
-            None
-        }
+        let kv = front.right_kv().ok()?;
+        Some(OccupiedEntry {
+            handle: kv.forget_node_type(),
+            length: &mut self.length,
+            _marker: PhantomData,
+        })
+    }
+
+    /// Removes and returns the first element in the map.
+    /// The key of this element is the minimum key that was in the map.
+    ///
+    /// # Examples
+    ///
+    /// Draining elements in ascending order, while keeping a usable map each iteration.
+    ///
+    /// ```
+    /// #![feature(map_first_last)]
+    /// use std::collections::BTreeMap;
+    ///
+    /// let mut map = BTreeMap::new();
+    /// map.insert(1, "a");
+    /// map.insert(2, "b");
+    /// while let Some((key, _val)) = map.pop_first() {
+    ///     assert!(map.iter().all(|(k, _v)| *k > key));
+    /// }
+    /// assert!(map.is_empty());
+    /// ```
+    #[unstable(feature = "map_first_last", issue = "62924")]
+    pub fn pop_first(&mut self) -> Option<(K, V)> {
+        self.first_entry().map(|entry| entry.remove_entry())
     }
 
     /// Returns the last key-value pair in the map.
@@ -716,11 +730,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.last_key_value(), Some((&2, &"a")));
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn last_key_value<T: ?Sized>(&self) -> Option<(&K, &V)>
-    where
-        T: Ord,
-        K: Borrow<T>,
-    {
+    pub fn last_key_value(&self) -> Option<(&K, &V)> {
         let back = self.root.as_ref()?.as_ref().last_leaf_edge();
         back.left_kv().ok().map(Handle::into_kv)
     }
@@ -730,36 +740,54 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// # Examples
     ///
-    /// Contrived way to `clear` a map:
-    ///
     /// ```
     /// #![feature(map_first_last)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
     /// map.insert(1, "a");
     /// map.insert(2, "b");
-    /// while let Some(entry) = map.last_entry() {
-    ///     let (key, val) = entry.remove_entry();
-    ///     assert!(!map.contains_key(&key));
+    /// if let Some(mut entry) = map.last_entry() {
+    ///     if *entry.key() > 0 {
+    ///         entry.insert("last");
+    ///     }
     /// }
+    /// assert_eq!(*map.get(&1).unwrap(), "a");
+    /// assert_eq!(*map.get(&2).unwrap(), "last");
     /// ```
     #[unstable(feature = "map_first_last", issue = "62924")]
-    pub fn last_entry<T: ?Sized>(&mut self) -> Option<OccupiedEntry<'_, K, V>>
-    where
-        T: Ord,
-        K: Borrow<T>,
-    {
+    pub fn last_entry(&mut self) -> Option<OccupiedEntry<'_, K, V>> {
         let back = self.root.as_mut()?.as_mut().last_leaf_edge();
-        if let Ok(kv) = back.left_kv() {
-            Some(OccupiedEntry {
-                handle: kv.forget_node_type(),
-                length: &mut self.length,
-                _marker: PhantomData,
-            })
-        } else {
-            None
-        }
+        let kv = back.left_kv().ok()?;
+        Some(OccupiedEntry {
+            handle: kv.forget_node_type(),
+            length: &mut self.length,
+            _marker: PhantomData,
+        })
+    }
+
+    /// Removes and returns the last element in the map.
+    /// The key of this element is the maximum key that was in the map.
+    ///
+    /// # Examples
+    ///
+    /// Draining elements in descending order, while keeping a usable map each iteration.
+    ///
+    /// ```
+    /// #![feature(map_first_last)]
+    /// use std::collections::BTreeMap;
+    ///
+    /// let mut map = BTreeMap::new();
+    /// map.insert(1, "a");
+    /// map.insert(2, "b");
+    /// while let Some((key, _val)) = map.pop_last() {
+    ///     assert!(map.iter().all(|(k, _v)| *k < key));
+    /// }
+    /// assert!(map.is_empty());
+    /// ```
+    #[unstable(feature = "map_first_last", issue = "62924")]
+    pub fn pop_last(&mut self) -> Option<(K, V)> {
+        self.last_entry().map(|entry| entry.remove_entry())
     }
 
     /// Returns `true` if the map contains a value for the specified key.

src/librustc_error_codes/error_codes/E0507.md

@@ -1,9 +1,4 @@
-You tried to move out of a value which was borrowed.
-
-This can also happen when using a type implementing `Fn` or `FnMut`, as neither
-allows moving out of them (they usually represent closures which can be called
-more than once). Much of the text following applies equally well to non-`FnOnce`
-closure bodies.
+A borrowed value was moved out.
 
 Erroneous code example:
 
@@ -32,6 +27,11 @@ you have three choices:
 * Somehow reclaim the ownership.
 * Implement the `Copy` trait on the type.
 
+This can also happen when using a type implementing `Fn` or `FnMut`, as neither
+allows moving out of them (they usually represent closures which can be called
+more than once). Much of the text following applies equally well to non-`FnOnce`
+closure bodies.
+
 Examples:
 
 ```

src/librustc_error_codes/error_codes/E0510.md

@@ -1,16 +1,29 @@
-Cannot mutate place in this match guard.
+The matched value was assigned in a match guard.
 
-When matching on a variable it cannot be mutated in the match guards, as this
-could cause the match to be non-exhaustive:
+Erroneous code example:
 
 ```compile_fail,E0510
 let mut x = Some(0);
 match x {
-    None => (),
-    Some(_) if { x = None; false } => (),
-    Some(v) => (), // No longer matches
+    None => {}
+    Some(_) if { x = None; false } => {} // error!
+    Some(_) => {}
 }
 ```
 
+When matching on a variable it cannot be mutated in the match guards, as this
+could cause the match to be non-exhaustive.
+
 Here executing `x = None` would modify the value being matched and require us
-to go "back in time" to the `None` arm.
+to go "back in time" to the `None` arm. To fix it, change the value in the match
+arm:
+
+```
+let mut x = Some(0);
+match x {
+    None => {}
+    Some(_) => {
+        x = None; // ok!
+    }
+}
+```

src/librustc_lint/unused.rs

@@ -355,6 +355,19 @@ impl From<UnusedDelimsCtx> for &'static str {
 trait UnusedDelimLint {
     const DELIM_STR: &'static str;
 
+    /// Due to `ref` pattern, there can be a difference between using
+    /// `{ expr }` and `expr` in pattern-matching contexts. This means
+    /// that we should only lint `unused_parens` and not `unused_braces`
+    /// in this case.
+    ///
+    /// ```rust
+    /// let mut a = 7;
+    /// let ref b = { a }; // We actually borrow a copy of `a` here.
+    /// a += 1; // By mutating `a` we invalidate any borrows of `a`.
+    /// assert_eq!(b + 1, a); // `b` does not borrow `a`, so we can still use it here.
+    /// ```
+    const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool;
+
     // this cannot be a constant is it refers to a static.
     fn lint(&self) -> &'static Lint;
 
@@ -454,7 +467,10 @@ trait UnusedDelimLint {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
         use rustc_ast::ast::ExprKind::*;
         let (value, ctx, followed_by_block, left_pos, right_pos) = match e.kind {
-            If(ref cond, ref block, ..) => {
+            // Do not lint `unused_braces` in `if let` expressions.
+            If(ref cond, ref block, ..)
+                if !matches!(cond.kind, Let(_, _)) || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
+            {
                 let left = e.span.lo() + rustc_span::BytePos(2);
                 let right = block.span.lo();
                 (cond, UnusedDelimsCtx::IfCond, true, Some(left), Some(right))
@@ -470,7 +486,7 @@ trait UnusedDelimLint {
                 (cond, UnusedDelimsCtx::ForIterExpr, true, None, Some(block.span.lo()))
             }
 
-            Match(ref head, _) => {
+            Match(ref head, _) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
                 let left = e.span.lo() + rustc_span::BytePos(5);
                 (head, UnusedDelimsCtx::MatchScrutineeExpr, true, Some(left), None)
             }
@@ -512,7 +528,7 @@ trait UnusedDelimLint {
 
     fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
         match s.kind {
-            StmtKind::Local(ref local) => {
+            StmtKind::Local(ref local) if Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX => {
                 if let Some(ref value) = local.init {
                     self.check_unused_delims_expr(
                         cx,
@@ -565,6 +581,8 @@ declare_lint_pass!(UnusedParens => [UNUSED_PARENS]);
 impl UnusedDelimLint for UnusedParens {
     const DELIM_STR: &'static str = "parentheses";
 
+    const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool = true;
+
     fn lint(&self) -> &'static Lint {
         UNUSED_PARENS
     }
@@ -736,6 +754,8 @@ declare_lint_pass!(UnusedBraces => [UNUSED_BRACES]);
 impl UnusedDelimLint for UnusedBraces {
     const DELIM_STR: &'static str = "braces";
 
+    const LINT_EXPR_IN_PATTERN_MATCHING_CTX: bool = false;
+
     fn lint(&self) -> &'static Lint {
         UNUSED_BRACES
     }

src/librustc_middle/mir/cache.rs

@@ -5,13 +5,15 @@ use rustc_data_structures::graph::{self, GraphPredecessors, GraphSuccessors};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_index::vec::IndexVec;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+use smallvec::SmallVec;
 use std::iter;
 use std::ops::{Deref, DerefMut, Index, IndexMut};
 use std::vec::IntoIter;
 
 #[derive(Clone, Debug)]
 pub struct Cache {
-    predecessors: Option<IndexVec<BasicBlock, Vec<BasicBlock>>>,
+    // Typically 95%+ of the inner vectors have 4 or fewer elements.
+    predecessors: Option<IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>>>,
 }
 
 impl rustc_serialize::Encodable for Cache {
@@ -44,7 +46,7 @@ impl Cache {
 
     pub fn ensure_predecessors(&mut self, body: &Body<'_>) {
         if self.predecessors.is_none() {
-            let mut result = IndexVec::from_elem(vec![], body.basic_blocks());
+            let mut result = IndexVec::from_elem(smallvec![], body.basic_blocks());
             for (bb, data) in body.basic_blocks().iter_enumerated() {
                 if let Some(ref term) = data.terminator {
                     for &tgt in term.successors() {
@@ -58,7 +60,11 @@ impl Cache {
     }
 
     /// This will recompute the predecessors cache if it is not available
-    fn predecessors(&mut self, body: &Body<'_>) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
+    // njn: typedef?
+    fn predecessors(
+        &mut self,
+        body: &Body<'_>,
+    ) -> &IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>> {
         self.ensure_predecessors(body);
         self.predecessors.as_ref().unwrap()
     }
@@ -137,7 +143,7 @@ impl BodyAndCache<'tcx> {
         self.cache.ensure_predecessors(&self.body);
     }
 
-    pub fn predecessors(&mut self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
+    pub fn predecessors(&mut self) -> &IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>> {
         self.cache.predecessors(&self.body)
     }
 
@@ -199,7 +205,7 @@ impl ReadOnlyBodyAndCache<'a, 'tcx> {
         Self { body, cache }
     }
 
-    pub fn predecessors(&self) -> &IndexVec<BasicBlock, Vec<BasicBlock>> {
+    pub fn predecessors(&self) -> &IndexVec<BasicBlock, SmallVec<[BasicBlock; 4]>> {
         self.cache.predecessors.as_ref().unwrap()
     }
 

src/librustc_middle/ty/flags.rs

@@ -28,7 +28,7 @@ impl FlagComputation {
     }
 
     fn add_flags(&mut self, flags: TypeFlags) {
-        self.flags = self.flags | (flags & TypeFlags::NOMINAL_FLAGS);
+        self.flags = self.flags | flags;
     }
 
     /// indicates that `self` refers to something at binding level `binder`