Rollup merge of #123431 - slanterns:literal_byte_character_c_string_stabilize, r=dtolnay

Stabilize `proc_macro_byte_character` and `proc_macro_c_str_literals`

This PR stabilizes `proc_macro_byte_character` and `proc_macro_c_str_literals`:

```rust
// proc_macro::Literal

impl Literal {
    pub fn byte_character(byte: u8) -> Literal;
    pub fn c_string(string: &CStr) -> Literal
}
```

<br>

Tracking issue: https://github.com/rust-lang/rust/issues/115268, https://github.com/rust-lang/rust/issues/119750.
Implementation PR: https://github.com/rust-lang/rust/pull/112711, https://github.com/rust-lang/rust/pull/119651.

FCPs already completed in their respective tracking issues.

Closes https://github.com/rust-lang/rust/issues/115268. Closes https://github.com/rust-lang/rust/issues/119750.

r? libs-api

library/proc_macro/src/lib.rs

@@ -1360,7 +1360,7 @@ impl Literal {
     }
 
     /// Byte character literal.
-    #[unstable(feature = "proc_macro_byte_character", issue = "115268")]
+    #[stable(feature = "proc_macro_byte_character", since = "CURRENT_RUSTC_VERSION")]
     pub fn byte_character(byte: u8) -> Literal {
         let string = [byte].escape_ascii().to_string();
         Literal::new(bridge::LitKind::Byte, &string, None)
@@ -1374,7 +1374,7 @@ impl Literal {
     }
 
     /// C string literal.
-    #[unstable(feature = "proc_macro_c_str_literals", issue = "119750")]
+    #[stable(feature = "proc_macro_c_str_literals", since = "CURRENT_RUSTC_VERSION")]
     pub fn c_string(string: &CStr) -> Literal {
         let string = string.to_bytes().escape_ascii().to_string();
         Literal::new(bridge::LitKind::CStr, &string, None)

tests/ui/feature-gates/feature-gate-proc_macro_byte_character.rs

@@ -1,10 +0,0 @@
-//@ force-host
-#![crate_type = "proc-macro"]
-
-extern crate proc_macro;
-
-use proc_macro::Literal;
-
-fn test() {
-    Literal::byte_character(b'a'); //~ ERROR use of unstable library feature 'proc_macro_byte_character'
-}

tests/ui/feature-gates/feature-gate-proc_macro_byte_character.stderr

@@ -1,13 +0,0 @@
-error[E0658]: use of unstable library feature 'proc_macro_byte_character'
-  --> $DIR/feature-gate-proc_macro_byte_character.rs:9:5
-   |
-LL |     Literal::byte_character(b'a');
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #115268 <https://github.com/rust-lang/rust/issues/115268> for more information
-   = help: add `#![feature(proc_macro_byte_character)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0658`.

tests/ui/feature-gates/feature-gate-proc_macro_c_str_literals.rs

@@ -1,11 +0,0 @@
-//@ edition: 2021
-//@ force-host
-#![crate_type = "proc-macro"]
-
-extern crate proc_macro;
-
-use proc_macro::Literal;
-
-fn test() {
-    Literal::c_string(c"a"); //~ ERROR use of unstable library feature 'proc_macro_c_str_literals'
-}

tests/ui/feature-gates/feature-gate-proc_macro_c_str_literals.stderr

@@ -1,13 +0,0 @@
-error[E0658]: use of unstable library feature 'proc_macro_c_str_literals'
-  --> $DIR/feature-gate-proc_macro_c_str_literals.rs:10:5
-   |
-LL |     Literal::c_string(c"a");
-   |     ^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #119750 <https://github.com/rust-lang/rust/issues/119750> for more information
-   = help: add `#![feature(proc_macro_c_str_literals)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0658`.

tests/ui/proc-macro/auxiliary/api/mod.rs

@@ -5,8 +5,6 @@
 #![crate_type = "proc-macro"]
 #![crate_name = "proc_macro_api_tests"]
 #![feature(proc_macro_span)]
-#![feature(proc_macro_byte_character)]
-#![feature(proc_macro_c_str_literals)]
 #![deny(dead_code)] // catch if a test function is never called
 
 extern crate proc_macro;