rust: use the new name Location::file_as_c_str() in Rust >= 1.91.0

As part of the stabilization of Location::file_with_nul(), it was brought
up that the with_nul() suffix usually means something else in Rust APIs,
so the API is being renamed prior to stabilization [1].

Thus, use the new name on new rustc versions.

Link: https://www.github.com/rust-lang/rust/pull/145928 [1]
Signed-off-by: Alice Ryhl <[e-mail]>
Reviewed-by: Boqun Feng <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[ Kept `cfg` separation. Reworded slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <[e-mail]>

init/Kconfig

···
 config RUSTC_HAS_FILE_WITH_NUL
 	def_bool RUSTC_VERSION >= 108900
 
+config RUSTC_HAS_FILE_AS_C_STR
+	def_bool RUSTC_VERSION >= 109100
+
 config PAHOLE_VERSION
 	int
 	default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))

rust/kernel/lib.rs

···
 
 /// Gets the C string file name of a [`Location`].
 ///
-/// If `file_with_nul()` is not available, returns a string that warns about it.
+/// If `Location::file_as_c_str()` is not available, returns a string that warns about it.
 ///
 /// [`Location`]: core::panic::Location
 ///
···
 ///     let caller = core::panic::Location::caller();
 ///
 ///     // Output:
-///     // - A path like "rust/kernel/example.rs" if file_with_nul() is available.
-///     // - "<Location::file_with_nul() not supported>" otherwise.
+///     // - A path like "rust/kernel/example.rs" if `file_as_c_str()` is available.
+///     // - "<Location::file_as_c_str() not supported>" otherwise.
 ///     let caller_file = file_from_location(caller);
 ///
 ///     // Prints out the message with caller's file name.
···
 /// ```
 #[inline]
 pub fn file_from_location<'a>(loc: &'a core::panic::Location<'a>) -> &'a core::ffi::CStr {
-    #[cfg(CONFIG_RUSTC_HAS_FILE_WITH_NUL)]
+    #[cfg(CONFIG_RUSTC_HAS_FILE_AS_C_STR)]
+    {
+        loc.file_as_c_str()
+    }
+
+    #[cfg(all(CONFIG_RUSTC_HAS_FILE_WITH_NUL, not(CONFIG_RUSTC_HAS_FILE_AS_C_STR)))]
     {
         loc.file_with_nul()
     }
···
     #[cfg(not(CONFIG_RUSTC_HAS_FILE_WITH_NUL))]
     {
         let _ = loc;
-        c"<Location::file_with_nul() not supported>"
+        c"<Location::file_as_c_str() not supported>"
     }
 }