Merge subtree update for toolchain nightly-2025-03-18

.github/workflows/update-subtree.yml

@@ -137,11 +137,14 @@ jobs:
       uses: peter-evans/create-pull-request@v7
       with:
         title: 'Update subtree/library to ${{ env.NEXT_TOOLCHAIN_DATE }}'
-        body: |
+        body: >
           This is an automated PR to update the subtree/library branch to the changes
-          from ${{ env.CURRENT_TOOLCHAIN_DATE }} (${{ env.CURRENT_COMMIT_HASH }})
-          to ${{ env.NEXT_TOOLCHAIN_DATE }} (${{ env.NEXT_COMMIT_HASH }}), inclusive.
-          **Do not merge this PR using the merge queue. Instead, use the rebase strategy.**
+          from ${{ env.CURRENT_TOOLCHAIN_DATE }} (rust-lang/rust@${{ env.CURRENT_COMMIT_HASH }})
+          to ${{ env.NEXT_TOOLCHAIN_DATE }} (rust-lang/rust@${{ env.NEXT_COMMIT_HASH }}), inclusive.
+
+          **Review this PR as usual, but do not merge this PR using the GitHub web interface.
+          Instead, once it is approved, use `git push` to literally push the changes to `subtree/library`
+          without any rebase or merge.**
         branch: update-subtree/library
         delete-branch: true
         base: subtree/library
@@ -151,20 +154,36 @@ jobs:
       if: ${{ env.MERGE_CONFLICTS != 'noop' && env.MERGE_PR_EXISTS == 'no' }}
       run: |
         cd verify-rust-std
-        if ! git rev-parse --verify subtree/library; then
+        # create-pull-request resets branches locally, implying that
+        # `subtree/library` no longer is what the above instructions created.
+        if [ "${SUBTREE_PR_EXISTS}" = "yes" ]; then
           git checkout -t -b subtree/library origin/update-subtree/library
+        else
+          git checkout subtree/library
+          git reset --hard origin/update-subtree/library
         fi
         git checkout main
 
+        # Tell git about the correct merge base to use, which is the subtree
+        # head that we last merged from.
+        PREV_SUBTREE_HEAD=$(git log --grep="^git-subtree-split:" | egrep '^[[:space:]]+git-subtree-split:' | awk '{print $2;exit}')
+        echo "Previous subtree head: ${PREV_SUBTREE_HEAD}"
+        git replace --graft subtree/library ${PREV_SUBTREE_HEAD}
+        git replace --graft main ${PREV_SUBTREE_HEAD}
+
         # This command may fail, which will require human intervention.
         if ! git \
             -c user.name=gitbot -c user.email=git@bot \
-            subtree merge --prefix=library subtree/library --squash; then
+            merge -Xsubtree=library subtree/library; then
           echo "MERGE_CONFLICTS=yes" >> $GITHUB_ENV
           git -c user.name=gitbot -c user.email=git@bot commit -a -m "Merge from $NEXT_COMMIT_HASH with conflicts"
         else
           echo "MERGE_CONFLICTS=no" >> $GITHUB_ENV
         fi
+        git replace -d subtree/library
+        git replace -d main~1
+        NEW_SUBTREE_HEAD=$(git rev-parse subtree/library)
+        echo "NEW_SUBTREE_HEAD=${NEW_SUBTREE_HEAD}" >> $GITHUB_ENV
 
         sed -i "s/^channel = \"nightly-.*\"/channel = \"nightly-${NEXT_TOOLCHAIN_DATE}\"/" rust-toolchain.toml
         git -c user.name=gitbot -c user.email=git@bot \
@@ -173,16 +192,22 @@ jobs:
         sed -i "s/commit = .*/commit = \"${KANI_COMMIT_HASH}\"/" tool_config/kani-version.toml
         git -c user.name=gitbot -c user.email=git@bot \
           commit -m "Update Kani version to ${KANI_COMMIT_HASH}" tool_config/kani-version.toml
+
     - name: Create Pull Request without conflicts
       if: ${{ env.MERGE_CONFLICTS == 'no' && env.MERGE_PR_EXISTS == 'no' }}
       uses: peter-evans/create-pull-request@v7
       with:
         title: 'Merge subtree update for toolchain nightly-${{ env.NEXT_TOOLCHAIN_DATE }}'
-        body: |
+        body: >
           This is an automated PR to merge library subtree updates
-          from ${{ env.CURRENT_TOOLCHAIN_DATE }} (${{ env.CURRENT_COMMIT_HASH }})
-          to ${{ env.NEXT_TOOLCHAIN_DATE }} (${{ env.NEXT_COMMIT_HASH }}), inclusive.
+          from ${{ env.CURRENT_TOOLCHAIN_DATE }} (rust-lang/rust@${{ env.CURRENT_COMMIT_HASH }})
+          to ${{ env.NEXT_TOOLCHAIN_DATE }} (rust-lang/rust@${{ env.NEXT_COMMIT_HASH }}), inclusive.
           This is a clean merge, no conflicts were detected.
+          **Do not remove or edit the following annotations:**
+
+          git-subtree-dir: library
+
+          git-subtree-split: ${{ env.NEW_SUBTREE_HEAD }}
         branch: sync-${{ env.NEXT_TOOLCHAIN_DATE }}
         delete-branch: true
         base: main
@@ -193,12 +218,17 @@ jobs:
       uses: peter-evans/create-pull-request@v7
       with:
         title: 'Merge subtree update for toolchain nightly-${{ env.NEXT_TOOLCHAIN_DATE }}'
-        body: |
+        body: >
           This is an automated PR to merge library subtree updates
-          from ${{ env.CURRENT_TOOLCHAIN_DATE }} (${{ env.CURRENT_COMMIT_HASH }})
-          to ${{ env.NEXT_TOOLCHAIN_DATE }} (${{ env.NEXT_COMMIT_HASH }}) (inclusive)
+          from ${{ env.CURRENT_TOOLCHAIN_DATE }} (rust-lang/rust@${{ env.CURRENT_COMMIT_HASH }})
+          to ${{ env.NEXT_TOOLCHAIN_DATE }} (rust-lang/rust@${{ env.NEXT_COMMIT_HASH }}) (inclusive)
           into main. `git merge` resulted in conflicts, which require manual resolution.
           Files were commited with merge conflict markers.
+          **Do not remove or edit the following annotations:**
+
+          git-subtree-dir: library
+
+          git-subtree-split: ${{ env.NEW_SUBTREE_HEAD }}
         branch: sync-${{ env.NEXT_TOOLCHAIN_DATE }}
         delete-branch: true
         base: main

library/Cargo.toml

@@ -8,6 +8,7 @@ members = [
 ]
 
 exclude = [
+  "literal-escaper",
   # stdarch has its own Cargo workspace
   "stdarch",
   "windows_targets"

library/alloc/src/sync.rs

@@ -84,9 +84,29 @@ macro_rules! acquire {
 ///
 /// Shared references in Rust disallow mutation by default, and `Arc` is no
 /// exception: you cannot generally obtain a mutable reference to something
-/// inside an `Arc`. If you need to mutate through an `Arc`, use
-/// [`Mutex`][mutex], [`RwLock`][rwlock], or one of the [`Atomic`][atomic]
-/// types.
+/// inside an `Arc`. If you do need to mutate through an `Arc`, you have several options:
+///
+/// 1. Use interior mutability with synchronization primitives like [`Mutex`][mutex],
+///    [`RwLock`][rwlock], or one of the [`Atomic`][atomic] types.
+///
+/// 2. Use clone-on-write semantics with [`Arc::make_mut`] which provides efficient mutation
+///    without requiring interior mutability. This approach clones the data only when
+///    needed (when there are multiple references) and can be more efficient when mutations
+///    are infrequent.
+///
+/// 3. Use [`Arc::get_mut`] when you know your `Arc` is not shared (has a reference count of 1),
+///    which provides direct mutable access to the inner value without any cloning.
+///
+/// ```
+/// use std::sync::Arc;
+///
+/// let mut data = Arc::new(vec![1, 2, 3]);
+///
+/// // This will clone the vector only if there are other references to it
+/// Arc::make_mut(&mut data).push(4);
+///
+/// assert_eq!(*data, vec![1, 2, 3, 4]);
+/// ```
 ///
 /// **Note**: This type is only available on platforms that support atomic
 /// loads and stores of pointers, which includes all platforms that support

library/alloc/src/vec/mod.rs

@@ -1252,6 +1252,19 @@ impl<T, A: Allocator> Vec<T, A> {
     /// vec.push(42);
     /// assert!(vec.capacity() >= 10);
     /// ```
+    ///
+    /// A vector with zero-sized elements will always have a capacity of usize::MAX:
+    ///
+    /// ```
+    /// #[derive(Clone)]
+    /// struct ZeroSized;
+    ///
+    /// fn main() {
+    ///     assert_eq!(std::mem::size_of::<ZeroSized>(), 0);
+    ///     let v = vec![ZeroSized; 0];
+    ///     assert_eq!(v.capacity(), usize::MAX);
+    /// }
+    /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_vec_string_slice", since = "CURRENT_RUSTC_VERSION")]

library/core/src/convert/num.rs

@@ -156,22 +156,42 @@ impl_from!(i16 => isize, #[stable(feature = "lossless_iusize_conv", since = "1.2
 // https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-951.pdf
 
 // Note: integers can only be represented with full precision in a float if
-// they fit in the significand, which is 24 bits in f32 and 53 bits in f64.
+// they fit in the significand, which is:
+// * 11 bits in f16
+// * 24 bits in f32
+// * 53 bits in f64
+// * 113 bits in f128
 // Lossy float conversions are not implemented at this time.
+// FIXME(f16_f128): The `f16`/`f128` impls `#[stable]` attributes should be changed to reference
+// `f16`/`f128` when they are stabilised (trait impls have to have a `#[stable]` attribute, but none
+// of the `f16`/`f128` impls can be used on stable as the `f16` and `f128` types are unstable).
 
 // signed integer -> float
+impl_from!(i8 => f16, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i8 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i8 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(i8 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i16 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i16 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(i16 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i32 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(i32 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+// FIXME(f16_f128): This impl would allow using `f128` on stable before it is stabilised.
+// impl_from!(i64 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 
 // unsigned integer -> float
+impl_from!(u8 => f16, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u8 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u8 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u8 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u16 => f16, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u16 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u16 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u16 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u32 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u32 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+// FIXME(f16_f128): This impl would allow using `f128` on stable before it is stabilised.
+// impl_from!(u64 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 
 // float -> float
 // FIXME(f16_f128): adding additional `From<{float}>` impls to `f32` breaks inference. See
@@ -183,20 +203,27 @@ impl_from!(f32 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0
 impl_from!(f64 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 
 macro_rules! impl_float_from_bool {
-    ($float:ty) => {
+    (
+        $float:ty $(;
+            doctest_prefix: $(#[doc = $doctest_prefix:literal])*
+            doctest_suffix: $(#[doc = $doctest_suffix:literal])*
+        )?
+    ) => {
         #[stable(feature = "float_from_bool", since = "1.68.0")]
         impl From<bool> for $float {
             #[doc = concat!("Converts a [`bool`] to [`", stringify!($float),"`] losslessly.")]
             /// The resulting value is positive `0.0` for `false` and `1.0` for `true` values.
             ///
             /// # Examples
             /// ```
+            $($(#[doc = $doctest_prefix])*)?
             #[doc = concat!("let x: ", stringify!($float)," = false.into();")]
             /// assert_eq!(x, 0.0);
             /// assert!(x.is_sign_positive());
             ///
             #[doc = concat!("let y: ", stringify!($float)," = true.into();")]
             /// assert_eq!(y, 1.0);
+            $($(#[doc = $doctest_suffix])*)?
             /// ```
             #[inline]
             fn from(small: bool) -> Self {
@@ -207,8 +234,27 @@ macro_rules! impl_float_from_bool {
 }
 
 // boolean -> float
+impl_float_from_bool!(
+    f16;
+    doctest_prefix:
+    // rustdoc doesn't remove the conventional space after the `///`
+    ///#![feature(f16)]
+    ///# #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    doctest_suffix:
+    ///# }
+);
 impl_float_from_bool!(f32);
 impl_float_from_bool!(f64);
+impl_float_from_bool!(
+    f128;
+    doctest_prefix:
+    ///#![feature(f128)]
+    ///# #[cfg(all(target_arch = "x86_64", target_os = "linux"))] {
+    ///
+    doctest_suffix:
+    ///# }
+);
 
 // no possible bounds violation
 macro_rules! impl_try_from_unbounded {

library/core/src/intrinsics/mod.rs

@@ -3664,7 +3664,8 @@ pub const fn ptr_metadata<P: ptr::Pointee<Metadata = M> + ?Sized, M>(ptr: *const
 /// For regions of memory which might overlap, use [`copy`] instead.
 ///
 /// `copy_nonoverlapping` is semantically equivalent to C's [`memcpy`], but
-/// with the argument order swapped.
+/// with the source and destination arguments swapped,
+/// and `count` counting the number of `T`s instead of bytes.
 ///
 /// The copy is "untyped" in the sense that data may be uninitialized or otherwise violate the
 /// requirements of `T`. The initialization state is preserved exactly.
@@ -3791,8 +3792,10 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
 /// If the source and destination will *never* overlap,
 /// [`copy_nonoverlapping`] can be used instead.
 ///
-/// `copy` is semantically equivalent to C's [`memmove`], but with the argument
-/// order swapped. Copying takes place as if the bytes were copied from `src`
+/// `copy` is semantically equivalent to C's [`memmove`], but
+/// with the source and destination arguments swapped,
+/// and `count` counting the number of `T`s instead of bytes.
+/// Copying takes place as if the bytes were copied from `src`
 /// to a temporary array and then copied from the array to `dst`.
 ///
 /// The copy is "untyped" in the sense that data may be uninitialized or otherwise violate the

library/core/src/ops/control_flow.rs

@@ -80,6 +80,7 @@ use crate::{convert, ops};
 /// [`Continue`]: ControlFlow::Continue
 #[stable(feature = "control_flow_enum_type", since = "1.55.0")]
 #[rustc_diagnostic_item = "ControlFlow"]
+#[must_use]
 // ControlFlow should not implement PartialOrd or Ord, per RFC 3058:
 // https://rust-lang.github.io/rfcs/3058-try-trait-v2.html#traits-for-controlflow
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]

library/literal-escaper/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "literal-escaper"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+std = { version = '1.0.0', optional = true, package = 'rustc-std-workspace-std' }
+
+[features]
+rustc-dep-of-std = ["dep:std"]

library/literal-escaper/README.md

@@ -0,0 +1,4 @@
+# literal-escaper
+
+This crate provides code to unescape string literals. It is used by `rustc_lexer`
+and `proc_macro`.