Fix overly restrictive lifetime in core::panic::Location::file return type

library/core/src/panic/location.rs

@@ -183,7 +183,7 @@ impl<'a> Location<'a> {
     #[must_use]
     #[stable(feature = "panic_hooks", since = "1.10.0")]
     #[rustc_const_stable(feature = "const_location_fields", since = "1.79.0")]
-    pub const fn file(&self) -> &str {
+    pub const fn file(&self) -> &'a str {
         // SAFETY: The filename is valid.
         unsafe { self.filename.as_ref() }
     }
@@ -195,7 +195,7 @@ impl<'a> Location<'a> {
     #[must_use]
     #[unstable(feature = "file_with_nul", issue = "141727")]
     #[inline]
-    pub const fn file_with_nul(&self) -> &CStr {
+    pub const fn file_with_nul(&self) -> &'a CStr {
         let filename = self.filename.as_ptr();
 
         // SAFETY: The filename is valid for `filename_len+1` bytes, so this addition can't

library/coretests/tests/panic/location.rs

@@ -47,11 +47,19 @@ fn location_const_column() {
     assert_eq!(COLUMN, 40);
 }
 
+#[test]
+fn location_file_lifetime<'x>() {
+    // Verify that the returned `&str`s lifetime is derived from the generic
+    // lifetime 'a, not the lifetime of `&self`, when calling `Location::file`.
+    // Test failure is indicated by a compile failure, not a runtime panic.
+    let _: for<'a> fn(&'a Location<'x>) -> &'x str = Location::file;
+}
+
 #[test]
 fn location_debug() {
     let f = format!("{:?}", Location::caller());
     assert!(f.contains(&format!("{:?}", file!())));
-    assert!(f.contains("52"));
+    assert!(f.contains("60"));
     assert!(f.contains("29"));
 }