Auto merge of #82982 - Dylan-DPC:rollup-mt497z7, r=Dylan-DPC

Rollup of 9 pull requests

Successful merges:

 - #81309 (always eagerly eval consts in Relate)
 - #82217 (Edition-specific preludes)
 - #82807 (rustdoc: Remove redundant enableSearchInput function)
 - #82924 (WASI: Switch to crt1-command.o to enable support for new-style commands)
 - #82949 (Do not attempt to unlock envlock in child process after a fork.)
 - #82955 (fix: wrong word)
 - #82962 (Treat header as first paragraph for shortened markdown descriptions)
 - #82976 (fix error message for copy(_nonoverlapping) overflow)
 - #82977 (Rename `Option::get_or_default` to `get_or_insert_default`)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

5 files changed, 55 insertions, 8 deletions

diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 247d39743be..8149858e103 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -302,6 +302,7 @@
 #![feature(panic_internals)]
 #![feature(panic_unwind)]
 #![feature(pin_static_ref)]
+#![feature(prelude_2021)]
 #![feature(prelude_import)]
 #![feature(ptr_internals)]
 #![feature(raw)]
diff --git a/library/std/src/prelude/mod.rs b/library/std/src/prelude/mod.rs
index eb2095b8196..505b5f3013b 100644
--- a/library/std/src/prelude/mod.rs
+++ b/library/std/src/prelude/mod.rs
@@ -84,3 +84,37 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 pub mod v1;
+
+/// The 2015 version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2015", issue = "none")]
+pub mod rust_2015 {
+    #[unstable(feature = "prelude_2015", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+}
+
+/// The 2018 version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2018", issue = "none")]
+pub mod rust_2018 {
+    #[unstable(feature = "prelude_2018", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+}
+
+/// The 2021 version of the prelude of The Rust Standard Library.
+///
+/// See the [module-level documentation](self) for more.
+#[unstable(feature = "prelude_2021", issue = "none")]
+pub mod rust_2021 {
+    #[unstable(feature = "prelude_2021", issue = "none")]
+    #[doc(no_inline)]
+    pub use super::v1::*;
+
+    #[unstable(feature = "prelude_2021", issue = "none")]
+    #[doc(no_inline)]
+    pub use core::prelude::rust_2021::*;
+}
diff --git a/library/std/src/prelude/v1.rs b/library/std/src/prelude/v1.rs
index 7181dc6e710..ec89bb6d2a4 100644
--- a/library/std/src/prelude/v1.rs
+++ b/library/std/src/prelude/v1.rs
@@ -1,6 +1,6 @@
 //! The first version of the prelude of The Rust Standard Library.
 //!
-//! See the [module-level documentation](../index.html) for more.
+//! See the [module-level documentation](super) for more.
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
diff --git a/library/std/src/sys/unix/ext/process.rs b/library/std/src/sys/unix/ext/process.rs
index 4e170a8bb1c..1276edc6af6 100644
--- a/library/std/src/sys/unix/ext/process.rs
+++ b/library/std/src/sys/unix/ext/process.rs
@@ -62,9 +62,14 @@ pub trait CommandExt: Sealed {
     /// `fork`. This primarily means that any modifications made to memory on
     /// behalf of this closure will **not** be visible to the parent process.
     /// This is often a very constrained environment where normal operations
-    /// like `malloc` or acquiring a mutex are not guaranteed to work (due to
+    /// like `malloc`, accessing environment variables through [`std::env`]
+    /// or acquiring a mutex are not guaranteed to work (due to
     /// other threads perhaps still running when the `fork` was run).
     ///
+    /// For further details refer to the [POSIX fork() specification]
+    /// and the equivalent documentation for any targeted
+    /// platform, especially the requirements around *async-signal-safety*.
+    ///
     /// This also means that all resources such as file descriptors and
     /// memory-mapped regions got duplicated. It is your responsibility to make
     /// sure that the closure does not violate library invariants by making
@@ -73,6 +78,10 @@ pub trait CommandExt: Sealed {
     /// When this closure is run, aspects such as the stdio file descriptors and
     /// working directory have successfully been changed, so output to these
     /// locations may not appear where intended.
+    ///
+    /// [POSIX fork() specification]:
+    ///     https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html
+    /// [`std::env`]: mod@crate::env
     #[stable(feature = "process_pre_exec", since = "1.34.0")]
     unsafe fn pre_exec<F>(&mut self, f: F) -> &mut process::Command
     where
diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs
index 2fdbabae277..2eb64a99e59 100644
--- a/library/std/src/sys/unix/process/process_unix.rs
+++ b/library/std/src/sys/unix/process/process_unix.rs
@@ -1,6 +1,7 @@
 use crate::convert::TryInto;
 use crate::fmt;
 use crate::io::{self, Error, ErrorKind};
+use crate::mem;
 use crate::ptr;
 use crate::sys;
 use crate::sys::cvt;
@@ -45,15 +46,14 @@ impl Command {
         //
         // Note that as soon as we're done with the fork there's no need to hold
         // a lock any more because the parent won't do anything and the child is
-        // in its own process.
-        let result = unsafe {
-            let _env_lock = sys::os::env_lock();
-            cvt(libc::fork())?
-        };
+        // in its own process. Thus the parent drops the lock guard while the child
+        // forgets it to avoid unlocking it on a new thread, which would be invalid.
+        let (env_lock, result) = unsafe { (sys::os::env_lock(), cvt(libc::fork())?) };
 
         let pid = unsafe {
             match result {
                 0 => {
+                    mem::forget(env_lock);
                     drop(input);
                     let Err(err) = self.do_exec(theirs, envp.as_ref());
                     let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
@@ -74,7 +74,10 @@ impl Command {
                     rtassert!(output.write(&bytes).is_ok());
                     libc::_exit(1)
                 }
-                n => n,
+                n => {
+                    drop(env_lock);
+                    n
+                }
             }
         };