Rollup of 6 pull requests

compiler/rustc_error_codes/src/error_codes.rs

@@ -516,7 +516,8 @@ E0793: include_str!("./error_codes/E0793.md"),
 E0794: include_str!("./error_codes/E0794.md"),
 }
 
-// Undocumented removed error codes. Note that many removed error codes are documented.
+// Undocumented removed error codes. Note that many removed error codes are kept in the list above
+// and marked as no-longer emitted with a note in the markdown file (see E0001 for an example).
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard
 //  E0019, // merged into E0015

library/alloc/src/alloc.rs

@@ -408,9 +408,10 @@ pub mod __alloc_error_handler {
         if unsafe { __rust_alloc_error_handler_should_panic != 0 } {
             panic!("memory allocation of {size} bytes failed")
         } else {
-            core::panicking::panic_nounwind_fmt(format_args!(
-                "memory allocation of {size} bytes failed"
-            ))
+            core::panicking::panic_nounwind_fmt(
+                format_args!("memory allocation of {size} bytes failed"),
+                /* force_no_backtrace */ false,
+            )
         }
     }
 }

library/core/src/panic/panic_info.rs

@@ -28,6 +28,7 @@ pub struct PanicInfo<'a> {
     message: Option<&'a fmt::Arguments<'a>>,
     location: &'a Location<'a>,
     can_unwind: bool,
+    force_no_backtrace: bool,
 }
 
 impl<'a> PanicInfo<'a> {
@@ -42,9 +43,10 @@ impl<'a> PanicInfo<'a> {
         message: Option<&'a fmt::Arguments<'a>>,
         location: &'a Location<'a>,
         can_unwind: bool,
+        force_no_backtrace: bool,
     ) -> Self {
         struct NoPayload;
-        PanicInfo { location, message, payload: &NoPayload, can_unwind }
+        PanicInfo { location, message, payload: &NoPayload, can_unwind, force_no_backtrace }
     }
 
     #[unstable(
@@ -141,6 +143,17 @@ impl<'a> PanicInfo<'a> {
     pub fn can_unwind(&self) -> bool {
         self.can_unwind
     }
+
+    #[unstable(
+        feature = "panic_internals",
+        reason = "internal details of the implementation of the `panic!` and related macros",
+        issue = "none"
+    )]
+    #[doc(hidden)]
+    #[inline]
+    pub fn force_no_backtrace(&self) -> bool {
+        self.force_no_backtrace
+    }
 }
 
 #[stable(feature = "panic_hook_display", since = "1.26.0")]

library/core/src/panicking.rs

@@ -61,7 +61,12 @@ pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
         fn panic_impl(pi: &PanicInfo<'_>) -> !;
     }
 
-    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), true);
+    let pi = PanicInfo::internal_constructor(
+        Some(&fmt),
+        Location::caller(),
+        /* can_unwind */ true,
+        /* force_no_backtrace */ false,
+    );
 
     // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
     unsafe { panic_impl(&pi) }
@@ -77,7 +82,7 @@ pub const fn panic_fmt(fmt: fmt::Arguments<'_>) -> ! {
 // and unwinds anyway, we will hit the "unwinding out of nounwind function" guard,
 // which causes a "panic in a function that cannot unwind".
 #[rustc_nounwind]
-pub fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>) -> ! {
+pub fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>, force_no_backtrace: bool) -> ! {
     if cfg!(feature = "panic_immediate_abort") {
         super::intrinsics::abort()
     }
@@ -90,7 +95,12 @@ pub fn panic_nounwind_fmt(fmt: fmt::Arguments<'_>) -> ! {
     }
 
     // PanicInfo with the `can_unwind` flag set to false forces an abort.
-    let pi = PanicInfo::internal_constructor(Some(&fmt), Location::caller(), false);
+    let pi = PanicInfo::internal_constructor(
+        Some(&fmt),
+        Location::caller(),
+        /* can_unwind */ false,
+        force_no_backtrace,
+    );
 
     // SAFETY: `panic_impl` is defined in safe Rust code and thus is safe to call.
     unsafe { panic_impl(&pi) }
@@ -123,7 +133,15 @@ pub const fn panic(expr: &'static str) -> ! {
 #[lang = "panic_nounwind"] // needed by codegen for non-unwinding panics
 #[rustc_nounwind]
 pub fn panic_nounwind(expr: &'static str) -> ! {
-    panic_nounwind_fmt(fmt::Arguments::new_const(&[expr]));
+    panic_nounwind_fmt(fmt::Arguments::new_const(&[expr]), /* force_no_backtrace */ false);
+}
+
+/// Like `panic_nounwind`, but also inhibits showing a backtrace.
+#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
+#[cfg_attr(feature = "panic_immediate_abort", inline)]
+#[rustc_nounwind]
+pub fn panic_nounwind_nobacktrace(expr: &'static str) -> ! {
+    panic_nounwind_fmt(fmt::Arguments::new_const(&[expr]), /* force_no_backtrace */ true);
 }
 
 #[inline]
@@ -172,9 +190,12 @@ fn panic_misaligned_pointer_dereference(required: usize, found: usize) -> ! {
         super::intrinsics::abort()
     }
 
-    panic_nounwind_fmt(format_args!(
-        "misaligned pointer dereference: address must be a multiple of {required:#x} but is {found:#x}"
-    ))
+    panic_nounwind_fmt(
+        format_args!(
+            "misaligned pointer dereference: address must be a multiple of {required:#x} but is {found:#x}"
+        ),
+        /* force_no_backtrace */ false,
+    )
 }
 
 /// Panic because we cannot unwind out of a function.
@@ -205,7 +226,7 @@ fn panic_cannot_unwind() -> ! {
 #[rustc_nounwind]
 fn panic_in_cleanup() -> ! {
     // Keep the text in sync with `UnwindTerminateReason::as_str` in `rustc_middle`.
-    panic_nounwind("panic in a destructor during cleanup")
+    panic_nounwind_nobacktrace("panic in a destructor during cleanup")
 }
 
 /// This function is used instead of panic_fmt in const eval.

library/core/src/time.rs

@@ -656,10 +656,10 @@ impl Duration {
     #[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
     pub const fn checked_div(self, rhs: u32) -> Option<Duration> {
         if rhs != 0 {
-            let secs = self.secs / (rhs as u64);
-            let carry = self.secs - secs * (rhs as u64);
-            let extra_nanos = carry * (NANOS_PER_SEC as u64) / (rhs as u64);
-            let nanos = self.nanos.0 / rhs + (extra_nanos as u32);
+            let (secs, extra_secs) = (self.secs / (rhs as u64), self.secs % (rhs as u64));
+            let (mut nanos, extra_nanos) = (self.nanos.0 / rhs, self.nanos.0 % rhs);
+            nanos +=
+                ((extra_secs * (NANOS_PER_SEC as u64) + extra_nanos as u64) / (rhs as u64)) as u32;
             debug_assert!(nanos < NANOS_PER_SEC);
             Some(Duration::new(secs, nanos))
         } else {

library/core/tests/time.rs

@@ -170,6 +170,7 @@ fn saturating_mul() {
 fn div() {
     assert_eq!(Duration::new(0, 1) / 2, Duration::new(0, 0));
     assert_eq!(Duration::new(1, 1) / 3, Duration::new(0, 333_333_333));
+    assert_eq!(Duration::new(1, 1) / 7, Duration::new(0, 142_857_143));
     assert_eq!(Duration::new(99, 999_999_000) / 100, Duration::new(0, 999_999_990));
 }
 

library/std/src/os/unix/net/tests.rs

@@ -662,7 +662,7 @@ fn test_send_vectored_fds_unix_stream() {
     }
 }
 
-#[cfg(any(target_os = "android", target_os = "linux", target_os = "freebsd"))]
+#[cfg(any(target_os = "android", target_os = "linux"))]
 #[test]
 #[cfg_attr(target_os = "android", ignore)] // Android SELinux rules prevent creating Unix sockets
 fn test_send_vectored_with_ancillary_to_unix_datagram() {

library/std/src/panicking.rs

@@ -246,7 +246,9 @@ fn default_hook(info: &PanicInfo<'_>) {
 pub fn panic_hook_with_disk_dump(info: &PanicInfo<'_>, path: Option<&crate::path::Path>) {
     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
-    let backtrace = if panic_count::get_count() >= 2 {
+    let backtrace = if info.force_no_backtrace() {
+        None
+    } else if panic_count::get_count() >= 2 {
         BacktraceStyle::full()
     } else {
         crate::panic::get_backtrace_style()
@@ -294,7 +296,7 @@ pub fn panic_hook_with_disk_dump(info: &PanicInfo<'_>, path: Option<&crate::path
                     }
                 }
             }
-            // If backtraces aren't supported, do nothing.
+            // If backtraces aren't supported or are forced-off, do nothing.
             None => {}
         }
     };
@@ -615,14 +617,23 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
     let loc = info.location().unwrap(); // The current implementation always returns Some
     let msg = info.message().unwrap(); // The current implementation always returns Some
     crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
+        // FIXME: can we just pass `info` along rather than taking it apart here, only to have
+        // `rust_panic_with_hook` construct a new `PanicInfo`?
         if let Some(msg) = msg.as_str() {
-            rust_panic_with_hook(&mut StrPanicPayload(msg), info.message(), loc, info.can_unwind());
+            rust_panic_with_hook(
+                &mut StrPanicPayload(msg),
+                info.message(),
+                loc,
+                info.can_unwind(),
+                info.force_no_backtrace(),
+            );
         } else {
             rust_panic_with_hook(
                 &mut PanicPayload::new(msg),
                 info.message(),
                 loc,
                 info.can_unwind(),
+                info.force_no_backtrace(),
             );
         }
     })
@@ -647,7 +658,13 @@ pub const fn begin_panic<M: Any + Send>(msg: M) -> ! {
 
     let loc = Location::caller();
     return crate::sys_common::backtrace::__rust_end_short_backtrace(move || {
-        rust_panic_with_hook(&mut PanicPayload::new(msg), None, loc, true)
+        rust_panic_with_hook(
+            &mut PanicPayload::new(msg),
+            None,
+            loc,
+            /* can_unwind */ true,
+            /* force_no_backtrace */ false,
+        )
     });
 
     struct PanicPayload<A> {
@@ -693,6 +710,7 @@ fn rust_panic_with_hook(
     message: Option<&fmt::Arguments<'_>>,
     location: &Location<'_>,
     can_unwind: bool,
+    force_no_backtrace: bool,
 ) -> ! {
     let must_abort = panic_count::increase(true);
 
@@ -707,14 +725,20 @@ fn rust_panic_with_hook(
             panic_count::MustAbort::AlwaysAbort => {
                 // Unfortunately, this does not print a backtrace, because creating
                 // a `Backtrace` will allocate, which we must to avoid here.
-                let panicinfo = PanicInfo::internal_constructor(message, location, can_unwind);
+                let panicinfo = PanicInfo::internal_constructor(
+                    message,
+                    location,
+                    can_unwind,
+                    force_no_backtrace,
+                );
                 rtprintpanic!("{panicinfo}\npanicked after panic::always_abort(), aborting.\n");
             }
         }
         crate::sys::abort_internal();
     }
 
-    let mut info = PanicInfo::internal_constructor(message, location, can_unwind);
+    let mut info =
+        PanicInfo::internal_constructor(message, location, can_unwind, force_no_backtrace);
     let hook = HOOK.read().unwrap_or_else(PoisonError::into_inner);
     match *hook {
         // Some platforms (like wasm) know that printing to stderr won't ever actually

library/std/src/time.rs

@@ -176,6 +176,14 @@ pub struct Instant(time::Instant);
 /// The size of a `SystemTime` struct may vary depending on the target operating
 /// system.
 ///
+/// A `SystemTime` does not count leap seconds.
+/// `SystemTime::now()`'s behaviour around a leap second
+/// is the same as the operating system's wall clock.
+/// The precise behaviour near a leap second
+/// (e.g. whether the clock appears to run slow or fast, or stop, or jump)
+/// depends on platform and configuration,
+/// so should not be relied on.
+///
 /// Example:
 ///
 /// ```no_run
@@ -461,13 +469,21 @@ impl fmt::Debug for Instant {
 impl SystemTime {
     /// An anchor in time which can be used to create new `SystemTime` instances or
     /// learn about where in time a `SystemTime` lies.
+    //
+    // NOTE! this documentation is duplicated, here and in std::time::UNIX_EPOCH.
+    // The two copies are not quite identical, because of the difference in naming.
     ///
     /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
     /// respect to the system clock. Using `duration_since` on an existing
     /// `SystemTime` instance can tell how far away from this point in time a
     /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
     /// `SystemTime` instance to represent another fixed point in time.
     ///
+    /// `duration_since(UNIX_EPOCH).unwrap().as_secs()` returns
+    /// the number of non-leap seconds since the start of 1970 UTC.
+    /// This is a POSIX `time_t` (as a `u64`),
+    /// and is the same time representation as used in many Internet protocols.
+    ///
     /// # Examples
     ///
     /// ```no_run
@@ -617,13 +633,21 @@ impl fmt::Debug for SystemTime {
 
 /// An anchor in time which can be used to create new `SystemTime` instances or
 /// learn about where in time a `SystemTime` lies.
+//
+// NOTE! this documentation is duplicated, here and in SystemTime::UNIX_EPOCH.
+// The two copies are not quite identical, because of the difference in naming.
 ///
 /// This constant is defined to be "1970-01-01 00:00:00 UTC" on all systems with
 /// respect to the system clock. Using `duration_since` on an existing
 /// [`SystemTime`] instance can tell how far away from this point in time a
 /// measurement lies, and using `UNIX_EPOCH + duration` can be used to create a
 /// [`SystemTime`] instance to represent another fixed point in time.
 ///
+/// `duration_since(UNIX_EPOCH).unwrap().as_secs()` returns
+/// the number of non-leap seconds since the start of 1970 UTC.
+/// This is a POSIX `time_t` (as a `u64`),
+/// and is the same time representation as used in many Internet protocols.
+///
 /// # Examples
 ///
 /// ```no_run

src/doc/style-guide/src/expressions.md

@@ -400,7 +400,12 @@ constructs. For example, a macro use `foo!(a, b, c)` can be parsed like a
 function call (ignoring the `!`), so format it using the rules for function
 calls.
 
-### Special case macros
+The style guide defines specific formatting for particular macros in the
+language or standard library. The style guide does not define formatting for
+any third-party macros, even if similar to those in the language or standard
+library.
+
+### Format string macros
 
 For macros which take a format string, if all other arguments are *small*,
 format the arguments before the format string on a single line if they fit, and

src/tools/miri/tests/fail/panic/double_panic.stderr

@@ -6,7 +6,6 @@ second
 stack backtrace:
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a destructor during cleanup
-stack backtrace:
 thread caused non-unwinding panic. aborting.
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/std/src/sys/PLATFORM/mod.rs:LL:CC
@@ -19,7 +18,7 @@ LL |     ABORT();
    = note: inside closure at RUSTLIB/std/src/panicking.rs:LL:CC
    = note: inside `std::sys_common::backtrace::__rust_end_short_backtrace::<[closure@std::panicking::begin_panic_handler::{closure#0}], !>` at RUSTLIB/std/src/sys_common/backtrace.rs:LL:CC
    = note: inside `std::panicking::begin_panic_handler` at RUSTLIB/std/src/panicking.rs:LL:CC
-   = note: inside `core::panicking::panic_nounwind` at RUSTLIB/core/src/panicking.rs:LL:CC
+   = note: inside `core::panicking::panic_nounwind_nobacktrace` at RUSTLIB/core/src/panicking.rs:LL:CC
    = note: inside `core::panicking::panic_in_cleanup` at RUSTLIB/core/src/panicking.rs:LL:CC
 note: inside `main`
   --> $DIR/double_panic.rs:LL:CC

src/tools/tidy/src/error_codes.rs

@@ -354,7 +354,12 @@ fn check_error_codes_used(
 
     for code in error_codes {
         if !found_codes.contains(code) && !no_longer_emitted.contains(code) {
-            errors.push(format!("Error code `{code}` exists, but is not emitted by the compiler!"))
+            errors.push(format!(
+                "Error code `{code}` exists, but is not emitted by the compiler!\n\
+                Please mark the code as no longer emitted by adding the following note to the top of the `EXXXX.md` file:\n\
+                `#### Note: this error code is no longer emitted by the compiler`\n\
+                Also, do not forget to mark doctests that no longer apply as `ignore (error is no longer emitted)`."
+            ));
         }
 
         if found_codes.contains(code) && no_longer_emitted.contains(code) {

tests/ui/backtrace.rs

@@ -94,7 +94,7 @@ fn runtest(me: &str) {
     #[cfg(not(panic = "abort"))]
     {
         // Make sure a stack trace is printed
-        let p = template(me).arg("double-fail").spawn().unwrap();
+        let p = template(me).arg("double-fail").env("RUST_BACKTRACE","0").spawn().unwrap();
         let out = p.wait_with_output().unwrap();
         assert!(!out.status.success());
         let s = str::from_utf8(&out.stderr).unwrap();
@@ -106,18 +106,18 @@ fn runtest(me: &str) {
                 contains_verbose_expected(s, "double"),
             "bad output3: {}", s
         );
+        // Make sure it's only one stack trace.
+        assert_eq!(s.split("stack backtrace").count(), 2);
 
         // Make sure a stack trace isn't printed too many times
-        //
-        // Currently it is printed 3 times ("once", "twice" and "panic in a destructor during
-        // cleanup") but in the future the last one may be removed.
+        // even with RUST_BACKTRACE=1. It should be printed twice.
         let p = template(me).arg("double-fail")
                                     .env("RUST_BACKTRACE", "1").spawn().unwrap();
         let out = p.wait_with_output().unwrap();
         assert!(!out.status.success());
         let s = str::from_utf8(&out.stderr).unwrap();
         let mut i = 0;
-        for _ in 0..3 {
+        for _ in 0..2 {
             i += s[i + 10..].find("stack backtrace").unwrap() + 10;
         }
         assert!(s[i + 10..].find("stack backtrace").is_none(),