Auto merge of rust-lang#70371 - Centril:rollup-ywi1vo3, r=Centril

Rollup of 8 pull requests

Successful merges:

 - rust-lang#70023 (clean up E0436 explanation)
 - rust-lang#70234 (#[track_caller] on core::ops::{Index, IndexMut}.)
 - rust-lang#70241 (Miri: move ModifiedStatic to ConstEval errors)
 - rust-lang#70342 (IoSlice/IoSliceMut should be Send and Sync)
 - rust-lang#70350 (Request "-Z unstable-options" for unstable options)
 - rust-lang#70355 (Clean up E0454)
 - rust-lang#70359 (must_use on split_off)
 - rust-lang#70368 (Mark hotplug_codegen_backend as ignore-stage1)

Failed merges:

r? @ghost

Author: bors

src/liballoc/collections/vec_deque.rs

@@ -1876,6 +1876,7 @@ impl<T> VecDeque<T> {
     /// assert_eq!(buf2, [2, 3]);
     /// ```
     #[inline]
+    #[must_use = "use `.truncate()` if you don't need the other half"]
     #[stable(feature = "split_off", since = "1.4.0")]
     pub fn split_off(&mut self, at: usize) -> Self {
         let len = self.len();

src/liballoc/string.rs

@@ -1461,6 +1461,7 @@ impl String {
     /// ```
     #[inline]
     #[stable(feature = "string_split_off", since = "1.16.0")]
+    #[must_use = "use `.truncate()` if you don't need the other half"]
     pub fn split_off(&mut self, at: usize) -> String {
         assert!(self.is_char_boundary(at));
         let other = self.vec.split_off(at);

src/liballoc/tests/string.rs

@@ -266,14 +266,14 @@ fn test_split_off_empty() {
 fn test_split_off_past_end() {
     let orig = "Hello, world!";
     let mut split = String::from(orig);
-    split.split_off(orig.len() + 1);
+    let _ = split.split_off(orig.len() + 1);
 }
 
 #[test]
 #[should_panic]
 fn test_split_off_mid_char() {
     let mut orig = String::from("山");
-    orig.split_off(1);
+    let _ = orig.split_off(1);
 }
 
 #[test]

src/libcore/ops/index.rs

@@ -65,6 +65,7 @@ pub trait Index<Idx: ?Sized> {
 
     /// Performs the indexing (`container[index]`) operation.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), track_caller)]
     fn index(&self, index: Idx) -> &Self::Output;
 }
 
@@ -166,5 +167,6 @@ see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#ind
 pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
     /// Performs the mutable indexing (`container[index]`) operation.
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), track_caller)]
     fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
 }

src/libcore/slice/mod.rs

@@ -2306,6 +2306,7 @@ impl<T> [T] {
     /// assert_eq!(&bytes, b"Hello, Wello!");
     /// ```
     #[stable(feature = "copy_within", since = "1.37.0")]
+    #[track_caller]
     pub fn copy_within<R: ops::RangeBounds<usize>>(&mut self, src: R, dest: usize)
     where
         T: Copy,
@@ -2721,18 +2722,21 @@ where
 
 #[inline(never)]
 #[cold]
+#[track_caller]
 fn slice_index_len_fail(index: usize, len: usize) -> ! {
     panic!("index {} out of range for slice of length {}", index, len);
 }
 
 #[inline(never)]
 #[cold]
+#[track_caller]
 fn slice_index_order_fail(index: usize, end: usize) -> ! {
     panic!("slice index starts at {} but ends at {}", index, end);
 }
 
 #[inline(never)]
 #[cold]
+#[track_caller]
 fn slice_index_overflow_fail() -> ! {
     panic!("attempted to index slice up to maximum usize");
 }
@@ -2804,11 +2808,13 @@ pub trait SliceIndex<T: ?Sized>: private_slice_index::Sealed {
     /// Returns a shared reference to the output at this location, panicking
     /// if out of bounds.
     #[unstable(feature = "slice_index_methods", issue = "none")]
+    #[cfg_attr(not(bootstrap), track_caller)]
     fn index(self, slice: &T) -> &Self::Output;
 
     /// Returns a mutable reference to the output at this location, panicking
     /// if out of bounds.
     #[unstable(feature = "slice_index_methods", issue = "none")]
+    #[cfg_attr(not(bootstrap), track_caller)]
     fn index_mut(self, slice: &mut T) -> &mut Self::Output;
 }
 

src/libcore/str/mod.rs

@@ -1794,6 +1794,7 @@ mod traits {
 
     #[inline(never)]
     #[cold]
+    #[track_caller]
     fn str_index_overflow_fail() -> ! {
         panic!("attempted to index str up to maximum usize");
     }
@@ -2185,6 +2186,7 @@ fn truncate_to_char_boundary(s: &str, mut max: usize) -> (bool, &str) {
 
 #[inline(never)]
 #[cold]
+#[track_caller]
 fn slice_error_fail(s: &str, begin: usize, end: usize) -> ! {
     const MAX_DISPLAY_LENGTH: usize = 256;
     let (truncated, s_trunc) = truncate_to_char_boundary(s, MAX_DISPLAY_LENGTH);

src/librustc/mir/interpret/error.rs

@@ -453,9 +453,6 @@ pub enum UnsupportedOpInfo {
     ReadForeignStatic(DefId),
     /// Could not find MIR for a function.
     NoMirFor(DefId),
-    /// Modified a static during const-eval.
-    /// FIXME: move this to `ConstEvalErrKind` through a machine hook.
-    ModifiedStatic,
     /// Encountered a pointer where we needed raw bytes.
     ReadPointerAsBytes,
     /// Encountered raw bytes where we needed a pointer.
@@ -471,12 +468,6 @@ impl fmt::Debug for UnsupportedOpInfo {
                 write!(f, "tried to read from foreign (extern) static {:?}", did)
             }
             NoMirFor(did) => write!(f, "could not load MIR for {:?}", did),
-            ModifiedStatic => write!(
-                f,
-                "tried to modify a static's initial value from another static's \
-                    initializer"
-            ),
-
             ReadPointerAsBytes => write!(f, "unable to turn pointer into raw bytes",),
             ReadBytesAsPointer => write!(f, "unable to turn bytes into a pointer"),
         }

src/librustc/ty/context.rs

@@ -984,6 +984,7 @@ pub struct GlobalCtxt<'tcx> {
     /// Stores the value of constants (and deduplicates the actual memory)
     allocation_interner: ShardedHashMap<&'tcx Allocation, ()>,
 
+    /// Stores memory for globals (statics/consts).
     pub alloc_map: Lock<interpret::AllocMap<'tcx>>,
 
     layout_interner: ShardedHashMap<&'tcx LayoutDetails, ()>,

src/librustc_error_codes/error_codes/E0436.md

@@ -1,5 +1,4 @@
-The functional record update syntax is only allowed for structs. (Struct-like
-enum variants don't qualify, for example.)
+The functional record update syntax was used on something other than a struct.
 
 Erroneous code example:
 
@@ -24,7 +23,9 @@ fn one_up_competitor(competitor_frequency: PublicationFrequency)
 }
 ```
 
-Rewrite the expression without functional record update syntax:
+The functional record update syntax is only allowed for structs (struct-like
+enum variants don't qualify, for example). To fix the previous code, rewrite the
+expression without functional record update syntax:
 
 ```
 enum PublicationFrequency {

src/librustc_error_codes/error_codes/E0454.md

@@ -1,4 +1,6 @@
-A link name was given with an empty name. Erroneous code example:
+A link name was given with an empty name.
+
+Erroneous code example:
 
 ```compile_fail,E0454
 #[link(name = "")] extern {}