Auto merge of #67342 - Centril:rollup-fl44n41, r=Centril

Rollup of 7 pull requests

Successful merges:

 - #65778 (Stabilize `std::{rc,sync}::Weak::{weak_count, strong_count}`)
 - #66570 (stabilize Result::map_or)
 - #66735 (Add str::strip_prefix and str::strip_suffix)
 - #66771 (Stabilize the `core::panic` module)
 - #67317 (fix type_name_of_val doc comment)
 - #67324 (Fix repetition in matches/mod.rs)
 - #67325 (cleanup with push_fake_read)

Failed merges:

r? @ghost

Author: bors

Diff for: src/liballoc/rc.rs

@@ -1836,7 +1836,7 @@ impl<T: ?Sized> Weak<T> {
     /// If `self` was created using [`Weak::new`], this will return 0.
     ///
     /// [`Weak::new`]: #method.new
-    #[unstable(feature = "weak_counts", issue = "57977")]
+    #[stable(feature = "weak_counts", since = "1.41.0")]
     pub fn strong_count(&self) -> usize {
         if let Some(inner) = self.inner() {
             inner.strong()
@@ -1847,20 +1847,16 @@ impl<T: ?Sized> Weak<T> {
 
     /// Gets the number of `Weak` pointers pointing to this allocation.
     ///
-    /// If `self` was created using [`Weak::new`], this will return `None`. If
-    /// not, the returned value is at least 1, since `self` still points to the
-    /// allocation.
-    ///
-    /// [`Weak::new`]: #method.new
-    #[unstable(feature = "weak_counts", issue = "57977")]
-    pub fn weak_count(&self) -> Option<usize> {
+    /// If no strong pointers remain, this will return zero.
+    #[stable(feature = "weak_counts", since = "1.41.0")]
+    pub fn weak_count(&self) -> usize {
         self.inner().map(|inner| {
             if inner.strong() > 0 {
                 inner.weak() - 1  // subtract the implicit weak ptr
             } else {
-                inner.weak()
+                0
             }
-        })
+        }).unwrap_or(0)
     }
 
     /// Returns `None` when the pointer is dangling and there is no allocated `RcBox`

Diff for: src/liballoc/rc/tests.rs

@@ -114,28 +114,28 @@ fn test_weak_count() {
 
 #[test]
 fn weak_counts() {
-    assert_eq!(Weak::weak_count(&Weak::<u64>::new()), None);
+    assert_eq!(Weak::weak_count(&Weak::<u64>::new()), 0);
     assert_eq!(Weak::strong_count(&Weak::<u64>::new()), 0);
 
     let a = Rc::new(0);
     let w = Rc::downgrade(&a);
     assert_eq!(Weak::strong_count(&w), 1);
-    assert_eq!(Weak::weak_count(&w), Some(1));
+    assert_eq!(Weak::weak_count(&w), 1);
     let w2 = w.clone();
     assert_eq!(Weak::strong_count(&w), 1);
-    assert_eq!(Weak::weak_count(&w), Some(2));
+    assert_eq!(Weak::weak_count(&w), 2);
     assert_eq!(Weak::strong_count(&w2), 1);
-    assert_eq!(Weak::weak_count(&w2), Some(2));
+    assert_eq!(Weak::weak_count(&w2), 2);
     drop(w);
     assert_eq!(Weak::strong_count(&w2), 1);
-    assert_eq!(Weak::weak_count(&w2), Some(1));
+    assert_eq!(Weak::weak_count(&w2), 1);
     let a2 = a.clone();
     assert_eq!(Weak::strong_count(&w2), 2);
-    assert_eq!(Weak::weak_count(&w2), Some(1));
+    assert_eq!(Weak::weak_count(&w2), 1);
     drop(a2);
     drop(a);
     assert_eq!(Weak::strong_count(&w2), 0);
-    assert_eq!(Weak::weak_count(&w2), Some(1));
+    assert_eq!(Weak::weak_count(&w2), 0);
     drop(w2);
 }
 

Diff for: src/liballoc/sync.rs

@@ -12,7 +12,7 @@ use core::sync::atomic;
 use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
 use core::borrow;
 use core::fmt;
-use core::cmp::{self, Ordering};
+use core::cmp::Ordering;
 use core::iter;
 use core::intrinsics::abort;
 use core::mem::{self, align_of, align_of_val, size_of_val};
@@ -1529,7 +1529,7 @@ impl<T: ?Sized> Weak<T> {
     /// If `self` was created using [`Weak::new`], this will return 0.
     ///
     /// [`Weak::new`]: #method.new
-    #[unstable(feature = "weak_counts", issue = "57977")]
+    #[stable(feature = "weak_counts", since = "1.41.0")]
     pub fn strong_count(&self) -> usize {
         if let Some(inner) = self.inner() {
             inner.strong.load(SeqCst)
@@ -1541,9 +1541,8 @@ impl<T: ?Sized> Weak<T> {
     /// Gets an approximation of the number of `Weak` pointers pointing to this
     /// allocation.
     ///
-    /// If `self` was created using [`Weak::new`], this will return 0. If not,
-    /// the returned value is at least 1, since `self` still points to the
-    /// allocation.
+    /// If `self` was created using [`Weak::new`], or if there are no remaining
+    /// strong pointers, this will return 0.
     ///
     /// # Accuracy
     ///
@@ -1552,31 +1551,22 @@ impl<T: ?Sized> Weak<T> {
     /// `Weak`s pointing to the same allocation.
     ///
     /// [`Weak::new`]: #method.new
-    #[unstable(feature = "weak_counts", issue = "57977")]
-    pub fn weak_count(&self) -> Option<usize> {
-        // Due to the implicit weak pointer added when any strong pointers are
-        // around, we cannot implement `weak_count` correctly since it
-        // necessarily requires accessing the strong count and weak count in an
-        // unsynchronized fashion. So this version is a bit racy.
+    #[stable(feature = "weak_counts", since = "1.41.0")]
+    pub fn weak_count(&self) -> usize {
         self.inner().map(|inner| {
-            let strong = inner.strong.load(SeqCst);
             let weak = inner.weak.load(SeqCst);
+            let strong = inner.strong.load(SeqCst);
             if strong == 0 {
-                // If the last `Arc` has *just* been dropped, it might not yet
-                // have removed the implicit weak count, so the value we get
-                // here might be 1 too high.
-                weak
+                0
             } else {
-                // As long as there's still at least 1 `Arc` around, subtract
-                // the implicit weak pointer.
-                // Note that the last `Arc` might get dropped between the 2
-                // loads we do above, removing the implicit weak pointer. This
-                // means that the value might be 1 too low here. In order to not
-                // return 0 here (which would happen if we're the only weak
-                // pointer), we guard against that specifically.
-                cmp::max(1, weak - 1)
+                // Since we observed that there was at least one strong pointer
+                // after reading the weak count, we know that the implicit weak
+                // reference (present whenever any strong references are alive)
+                // was still around when we observed the weak count, and can
+                // therefore safely subtract it.
+                weak - 1
             }
-        })
+        }).unwrap_or(0)
     }
 
     /// Returns `None` when the pointer is dangling and there is no allocated `ArcInner`,

Diff for: src/liballoc/sync/tests.rs

@@ -62,28 +62,28 @@ fn test_arc_get_mut() {
 
 #[test]
 fn weak_counts() {
-    assert_eq!(Weak::weak_count(&Weak::<u64>::new()), None);
+    assert_eq!(Weak::weak_count(&Weak::<u64>::new()), 0);
     assert_eq!(Weak::strong_count(&Weak::<u64>::new()), 0);
 
     let a = Arc::new(0);
     let w = Arc::downgrade(&a);
     assert_eq!(Weak::strong_count(&w), 1);
-    assert_eq!(Weak::weak_count(&w), Some(1));
+    assert_eq!(Weak::weak_count(&w), 1);
     let w2 = w.clone();
     assert_eq!(Weak::strong_count(&w), 1);
-    assert_eq!(Weak::weak_count(&w), Some(2));
+    assert_eq!(Weak::weak_count(&w), 2);
     assert_eq!(Weak::strong_count(&w2), 1);
-    assert_eq!(Weak::weak_count(&w2), Some(2));
+    assert_eq!(Weak::weak_count(&w2), 2);
     drop(w);
     assert_eq!(Weak::strong_count(&w2), 1);
-    assert_eq!(Weak::weak_count(&w2), Some(1));
+    assert_eq!(Weak::weak_count(&w2), 1);
     let a2 = a.clone();
     assert_eq!(Weak::strong_count(&w2), 2);
-    assert_eq!(Weak::weak_count(&w2), Some(1));
+    assert_eq!(Weak::weak_count(&w2), 1);
     drop(a2);
     drop(a);
     assert_eq!(Weak::strong_count(&w2), 0);
-    assert_eq!(Weak::weak_count(&w2), Some(1));
+    assert_eq!(Weak::weak_count(&w2), 0);
     drop(w2);
 }
 

Diff for: src/libcore/any.rs

@@ -476,7 +476,7 @@ pub const fn type_name<T: ?Sized>() -> &'static str {
 ///
 /// This is intended for diagnostic use. The exact contents and format of the
 /// string are not specified, other than being a best-effort description of the
-/// type. For example, `type_name_of::<Option<String>>(None)` could return the
+/// type. For example, `type_name_of::<Option<String>>(None)` could return
 /// `"Option<String>"` or `"std::option::Option<std::string::String>"`, but not
 /// `"foobar"`. In addition, the output may change between versions of the
 /// compiler.

Diff for: src/libcore/panic.rs

@@ -1,8 +1,6 @@
 //! Panic support in the standard library.
 
-#![unstable(feature = "core_panic_info",
-            reason = "newly available in libcore",
-            issue = "44489")]
+#![stable(feature = "core_panic_info", since = "1.41.0")]
 
 use crate::any::Any;
 use crate::fmt;
@@ -39,10 +37,10 @@ pub struct PanicInfo<'a> {
 }
 
 impl<'a> PanicInfo<'a> {
-    #![unstable(feature = "panic_internals",
-                reason = "internal details of the implementation of the `panic!` \
-                          and related macros",
-                issue = "0")]
+    #[unstable(feature = "panic_internals",
+               reason = "internal details of the implementation of the `panic!` \
+                         and related macros",
+               issue = "0")]
     #[doc(hidden)]
     #[inline]
     pub fn internal_constructor(
@@ -57,6 +55,10 @@ impl<'a> PanicInfo<'a> {
         }
     }
 
+    #[unstable(feature = "panic_internals",
+               reason = "internal details of the implementation of the `panic!` \
+                         and related macros",
+               issue = "0")]
     #[doc(hidden)]
     #[inline]
     pub fn set_payload(&mut self, info: &'a (dyn Any + Send)) {
@@ -90,7 +92,7 @@ impl<'a> PanicInfo<'a> {
     /// returns that message ready to be used for example with [`fmt::write`]
     ///
     /// [`fmt::write`]: ../fmt/fn.write.html
-    #[unstable(feature = "panic_info_message", issue = "44489")]
+    #[unstable(feature = "panic_info_message", issue = "66745")]
     pub fn message(&self) -> Option<&fmt::Arguments<'_>> {
         self.message
     }

Diff for: src/libcore/result.rs

@@ -520,15 +520,14 @@ impl<T, E> Result<T, E> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(result_map_or)]
     /// let x: Result<_, &str> = Ok("foo");
     /// assert_eq!(x.map_or(42, |v| v.len()), 3);
     ///
     /// let x: Result<&str, _> = Err("bar");
     /// assert_eq!(x.map_or(42, |v| v.len()), 42);
     /// ```
     #[inline]
-    #[unstable(feature = "result_map_or", issue = "66293")]
+    #[stable(feature = "result_map_or", since = "1.41.0")]
     pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U {
         match self {
             Ok(t) => f(t),

Diff for: src/libcore/str/mod.rs

@@ -8,7 +8,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use self::pattern::Pattern;
-use self::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
+use self::pattern::{Searcher, SearchStep, ReverseSearcher, DoubleEndedSearcher};
 
 use crate::char;
 use crate::fmt::{self, Write};
@@ -3798,6 +3798,77 @@ impl str {
         }
     }
 
+    /// Returns a string slice with the prefix removed.
+    ///
+    /// If the string starts with the pattern `prefix`, `Some` is returned with the substring where
+    /// the prefix is removed. Unlike `trim_start_matches`, this method removes the prefix exactly
+    /// once.
+    ///
+    /// If the string does not start with `prefix`, `None` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(str_strip)]
+    ///
+    /// assert_eq!("foobar".strip_prefix("foo"), Some("bar"));
+    /// assert_eq!("foobar".strip_prefix("bar"), None);
+    /// assert_eq!("foofoo".strip_prefix("foo"), Some("foo"));
+    /// ```
+    #[must_use = "this returns the remaining substring as a new slice, \
+                  without modifying the original"]
+    #[unstable(feature = "str_strip", reason = "newly added", issue = "67302")]
+    pub fn strip_prefix<'a, P: Pattern<'a>>(&'a self, prefix: P) -> Option<&'a str> {
+        let mut matcher = prefix.into_searcher(self);
+        if let SearchStep::Match(start, len) = matcher.next() {
+            debug_assert_eq!(start, 0, "The first search step from Searcher \
+                must include the first character");
+            unsafe {
+                // Searcher is known to return valid indices.
+                Some(self.get_unchecked(len..))
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Returns a string slice with the suffix removed.
+    ///
+    /// If the string ends with the pattern `suffix`, `Some` is returned with the substring where
+    /// the suffix is removed. Unlike `trim_end_matches`, this method removes the suffix exactly
+    /// once.
+    ///
+    /// If the string does not end with `suffix`, `None` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(str_strip)]
+    /// assert_eq!("barfoo".strip_suffix("foo"), Some("bar"));
+    /// assert_eq!("barfoo".strip_suffix("bar"), None);
+    /// assert_eq!("foofoo".strip_suffix("foo"), Some("foo"));
+    /// ```
+    #[must_use = "this returns the remaining substring as a new slice, \
+                  without modifying the original"]
+    #[unstable(feature = "str_strip", reason = "newly added", issue = "67302")]
+    pub fn strip_suffix<'a, P>(&'a self, suffix: P) -> Option<&'a str>
+    where
+        P: Pattern<'a>,
+        <P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
+    {
+        let mut matcher = suffix.into_searcher(self);
+        if let SearchStep::Match(start, end) = matcher.next_back() {
+            debug_assert_eq!(end, self.len(), "The first search step from ReverseSearcher \
+                must include the last character");
+            unsafe {
+                // Searcher is known to return valid indices.
+                Some(self.get_unchecked(..start))
+            }
+        } else {
+            None
+        }
+    }
+
     /// Returns a string slice with all suffixes that match a pattern
     /// repeatedly removed.
     ///

Diff for: src/librustc_mir/build/cfg.rs

@@ -59,6 +59,18 @@ impl<'tcx> CFG<'tcx> {
         ));
     }
 
+    pub fn push_fake_read(
+        &mut self,
+        block: BasicBlock,
+        source_info: SourceInfo,
+        cause: FakeReadCause,
+        place: Place<'tcx>,
+    ) {
+        let kind = StatementKind::FakeRead(cause, box place);
+        let stmt = Statement { source_info, kind };
+        self.push(block, stmt);
+    }
+
     pub fn terminate(&mut self,
                      block: BasicBlock,
                      source_info: SourceInfo,

Diff for: src/librustc_mir/build/expr/as_place.rs

@@ -484,24 +484,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
     fn read_fake_borrows(
         &mut self,
-        block: BasicBlock,
+        bb: BasicBlock,
         fake_borrow_temps: &mut Vec<Local>,
         source_info: SourceInfo,
     ) {
         // All indexes have been evaluated now, read all of the
         // fake borrows so that they are live across those index
         // expressions.
         for temp in fake_borrow_temps {
-            self.cfg.push(
-                block,
-                Statement {
-                    source_info,
-                    kind: StatementKind::FakeRead(
-                        FakeReadCause::ForIndex,
-                        Box::new(Place::from(*temp)),
-                    )
-                }
-            );
+            self.cfg.push_fake_read(bb, source_info, FakeReadCause::ForIndex, Place::from(*temp));
         }
     }
 }