7 files changed, 71 insertions, 13 deletions
diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs
index 993ae723229..b18508186a6 100644
--- a/library/core/src/macros/mod.rs
+++ b/library/core/src/macros/mod.rs
@@ -967,6 +967,34 @@ pub(crate) mod builtin {
         ($($e:ident),+ $(,)?) => {{ /* compiler built-in */ }};
     }
 
+    /// Concatenates literals into a byte slice.
+    ///
+    /// This macro takes any number of comma-separated literals, and concatenates them all into
+    /// one, yielding an expression of type `&[u8, _]`, which represents all of the literals
+    /// concatenated left-to-right. The literals passed can be any combination of:
+    ///
+    /// - byte literals (`b'r'`)
+    /// - byte strings (`b"Rust"`)
+    /// - arrays of bytes/numbers (`[b'A', 66, b'C']`)
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(concat_bytes)]
+    ///
+    /// # fn main() {
+    /// let s: &[u8; 6] = concat_bytes!(b'A', b"BC", [68, b'E', 70]);
+    /// assert_eq!(s, b"ABCDEF");
+    /// # }
+    /// ```
+    #[cfg(not(bootstrap))]
+    #[unstable(feature = "concat_bytes", issue = "87555")]
+    #[rustc_builtin_macro]
+    #[macro_export]
+    macro_rules! concat_bytes {
+        ($($e:literal),+ $(,)?) => {{ /* compiler built-in */ }};
+    }
+
     /// Concatenates literals into a static string slice.
     ///
     /// This macro takes any number of comma-separated literals, yielding an
diff --git a/library/core/src/prelude/v1.rs b/library/core/src/prelude/v1.rs
index 6b51ef5b012..8705eb39468 100644
--- a/library/core/src/prelude/v1.rs
+++ b/library/core/src/prelude/v1.rs
@@ -61,6 +61,15 @@ pub use crate::{
 };
 
 #[unstable(
+    feature = "concat_bytes",
+    issue = "87555",
+    reason = "`concat_bytes` is not stable enough for use and is subject to change"
+)]
+#[cfg(not(bootstrap))]
+#[doc(no_inline)]
+pub use crate::concat_bytes;
+
+#[unstable(
     feature = "asm",
     issue = "72016",
     reason = "inline assembly is not stable enough for use and is subject to change"
diff --git a/library/std/src/env.rs b/library/std/src/env.rs
index c6af708f6cd..c06928647d3 100644
--- a/library/std/src/env.rs
+++ b/library/std/src/env.rs
@@ -583,28 +583,25 @@ pub fn home_dir() -> Option<PathBuf> {
 /// may result in "insecure temporary file" security vulnerabilities. Consider
 /// using a crate that securely creates temporary files or directories.
 ///
-/// # Unix
+/// # Platform-specific behavior
 ///
-/// Returns the value of the `TMPDIR` environment variable if it is
+/// On Unix, returns the value of the `TMPDIR` environment variable if it is
 /// set, otherwise for non-Android it returns `/tmp`. If Android, since there
 /// is no global temporary folder (it is usually allocated per-app), it returns
 /// `/data/local/tmp`.
+/// On Windows, the behavior is equivalent to that of [`GetTempPath2`][GetTempPath2] /
+/// [`GetTempPath`][GetTempPath], which this function uses internally.
+/// Note that, this [may change in the future][changes].
 ///
-/// # Windows
-///
-/// Returns the value of, in order, the `TMP`, `TEMP`,
-/// `USERPROFILE` environment variable if any are set and not the empty
-/// string. Otherwise, `temp_dir` returns the path of the Windows directory.
-/// This behavior is identical to that of [`GetTempPath`][msdn], which this
-/// function uses internally.
-///
-/// [msdn]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppatha
+/// [changes]: io#platform-specific-behavior
+/// [GetTempPath2]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppath2a
+/// [GetTempPath]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppatha
 ///
 /// ```no_run
 /// use std::env;
 ///
 /// fn main() {
-///     let mut dir = env::temp_dir();
+///     let dir = env::temp_dir();
 ///     println!("Temporary directory: {}", dir.display());
 /// }
 /// ```
diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 67846e78835..367f072ffc7 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -250,6 +250,7 @@
 #![feature(cfg_target_thread_local)]
 #![feature(char_error_internals)]
 #![feature(char_internals)]
+#![cfg_attr(not(bootstrap), feature(concat_bytes))]
 #![feature(concat_idents)]
 #![feature(const_cstr_unchecked)]
 #![feature(const_fn_floating_point_arithmetic)]
@@ -576,6 +577,14 @@ pub use core::{
     log_syntax, module_path, option_env, stringify, trace_macros,
 };
 
+#[unstable(
+    feature = "concat_bytes",
+    issue = "87555",
+    reason = "`concat_bytes` is not stable enough for use and is subject to change"
+)]
+#[cfg(not(bootstrap))]
+pub use core::concat_bytes;
+
 #[stable(feature = "core_primitive", since = "1.43.0")]
 pub use core::primitive;
 
diff --git a/library/std/src/prelude/v1.rs b/library/std/src/prelude/v1.rs
index 772044f0149..9b23aa37e31 100644
--- a/library/std/src/prelude/v1.rs
+++ b/library/std/src/prelude/v1.rs
@@ -46,6 +46,15 @@ pub use core::prelude::v1::{
 };
 
 #[unstable(
+    feature = "concat_bytes",
+    issue = "87555",
+    reason = "`concat_bytes` is not stable enough for use and is subject to change"
+)]
+#[cfg(not(bootstrap))]
+#[doc(no_inline)]
+pub use core::prelude::v1::concat_bytes;
+
+#[unstable(
     feature = "asm",
     issue = "72016",
     reason = "inline assembly is not stable enough for use and is subject to change"
diff --git a/library/std/src/sys/windows/c.rs b/library/std/src/sys/windows/c.rs
index 50c4547de85..b87b6b5d88e 100644
--- a/library/std/src/sys/windows/c.rs
+++ b/library/std/src/sys/windows/c.rs
@@ -1110,6 +1110,12 @@ compat_fn! {
                                           -> () {
         GetSystemTimeAsFileTime(lpSystemTimeAsFileTime)
     }
+
+    // >= Win11 / Server 2022
+    // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettemppath2a
+    pub fn GetTempPath2W(nBufferLength: DWORD, lpBuffer: LPCWSTR) -> DWORD {
+        GetTempPathW(nBufferLength, lpBuffer)
+    }
 }
 
 compat_fn! {
diff --git a/library/std/src/sys/windows/os.rs b/library/std/src/sys/windows/os.rs
index b5209aa690b..5f8556c3bc3 100644
--- a/library/std/src/sys/windows/os.rs
+++ b/library/std/src/sys/windows/os.rs
@@ -275,7 +275,7 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
 }
 
 pub fn temp_dir() -> PathBuf {
-    super::fill_utf16_buf(|buf, sz| unsafe { c::GetTempPathW(sz, buf) }, super::os2path).unwrap()
+    super::fill_utf16_buf(|buf, sz| unsafe { c::GetTempPath2W(sz, buf) }, super::os2path).unwrap()
 }
 
 #[cfg(not(target_vendor = "uwp"))]