Stabilize format_args_ln!

`format_args_ln!` is generally useful for implementations of formatting
macros, and it has clear semantics and a clear interface.

Author: joshtriplett

library/core/src/macros/mod.rs

@@ -549,7 +549,6 @@ macro_rules! write {
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "writeln_macro")]
-#[allow_internal_unstable(format_args_ln)]
 macro_rules! writeln {
     ($dst:expr $(,)?) => {
         $crate::write!($dst, "\n")
@@ -896,12 +895,7 @@ pub(crate) mod builtin {
     }
 
     /// Same as [`format_args`], but adds a newline in the end.
-    #[unstable(
-        feature = "format_args_ln",
-        issue = "none",
-        reason = "`format_args_ln` is only for internal \
-                  language use and is subject to change"
-    )]
+    #[stable(feature = "format_args_ln", since = "1.63.0")]
     #[allow_internal_unstable(fmt_internals)]
     #[cfg_attr(bootstrap, rustc_builtin_macro(format_args_nl))]
     #[cfg_attr(not(bootstrap), rustc_builtin_macro)]

library/std/src/lib.rs

@@ -318,7 +318,6 @@
 #![feature(core_panic)]
 #![feature(custom_test_frameworks)]
 #![feature(edition_panic)]
-#![feature(format_args_ln)]
 #![feature(log_syntax)]
 #![feature(once_cell)]
 #![feature(saturating_int_impl)]

library/std/src/macros.rs

@@ -97,7 +97,7 @@ macro_rules! print {
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "println_macro")]
-#[allow_internal_unstable(print_internals, format_args_ln)]
+#[allow_internal_unstable(print_internals)]
 macro_rules! println {
     () => {
         $crate::print!("\n")
@@ -163,7 +163,7 @@ macro_rules! eprint {
 #[macro_export]
 #[stable(feature = "eprint", since = "1.19.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "eprintln_macro")]
-#[allow_internal_unstable(print_internals, format_args_ln)]
+#[allow_internal_unstable(print_internals)]
 macro_rules! eprintln {
     () => {
         $crate::eprint!("\n")

src/test/ui/feature-gates/feature-gate-format_args_nl.rs

@@ -1,7 +1,6 @@
 // check-pass
 
 #![allow(non_upper_case_globals)]
-#![feature(format_args_ln)]
 
 static arg0: () = ();