Auto merge of #101037 - GuillaumeGomez:rollup-opn6kj1, r=GuillaumeGomez

Rollup of 8 pull requests

Successful merges:

 - #95005 (BTree: evaluate static type-related check at compile time)
 - #99742 (Add comments about stdout locking)
 - #100128 (Document that `RawWakerVTable` functions must be thread-safe.)
 - #100956 (Reduce right-side DOM size)
 - #101006 (Fix doc cfg on reexports)
 - #101012 (rustdoc: remove unused CSS for `.variants_table`)
 - #101023 (rustdoc: remove `type="text/css"` from stylesheet links)
 - #101031 (Remove unused build dependency)

Failed merges:

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

1 files changed, 22 insertions, 0 deletions

diff --git a/library/std/src/macros.rs b/library/std/src/macros.rs
index ce2a979475c..a5003c66fca 100644
--- a/library/std/src/macros.rs
+++ b/library/std/src/macros.rs
@@ -27,12 +27,23 @@ macro_rules! panic {
 /// necessary to use [`io::stdout().flush()`][flush] to ensure the output is emitted
 /// immediately.
 ///
+/// The `print!` macro will lock the standard output on each call. If you call
+/// `print!` within a hot loop, this behavior may be the bottleneck of the loop.
+/// To avoid this, lock stdout with [`io::stdout().lock()`][lock]:
+/// ```
+/// use std::io::{stdout, Write};
+///
+/// let mut lock = stdout().lock();
+/// write!(lock, "hello world").unwrap();
+/// ```
+///
 /// Use `print!` only for the primary output of your program. Use
 /// [`eprint!`] instead to print error and progress messages.
 ///
 /// [flush]: crate::io::Write::flush
 /// [`println!`]: crate::println
 /// [`eprint!`]: crate::eprint
+/// [lock]: crate::io::Stdout
 ///
 /// # Panics
 ///
@@ -75,11 +86,22 @@ macro_rules! print {
 /// This macro uses the same syntax as [`format!`], but writes to the standard output instead.
 /// See [`std::fmt`] for more information.
 ///
+/// The `println!` macro will lock the standard output on each call. If you call
+/// `println!` within a hot loop, this behavior may be the bottleneck of the loop.
+/// To avoid this, lock stdout with [`io::stdout().lock()`][lock]:
+/// ```
+/// use std::io::{stdout, Write};
+///
+/// let mut lock = stdout().lock();
+/// writeln!(lock, "hello world").unwrap();
+/// ```
+///
 /// Use `println!` only for the primary output of your program. Use
 /// [`eprintln!`] instead to print error and progress messages.
 ///
 /// [`std::fmt`]: crate::fmt
 /// [`eprintln!`]: crate::eprintln
+/// [lock]: crate::io::Stdout
 ///
 /// # Panics
 ///