added regression test for core::panic::Location::file's lifetime

Author: ijchen

library/core/tests/panic/location.rs

@@ -0,0 +1,39 @@
+use core::panic::Location;
+
+// Note: Some of the following tests depend on the source location,
+// so please be careful when editing this file.
+
+#[test]
+fn location_const_caller() {
+    const _CALLER_REFERENCE: &Location<'static> = Location::caller();
+    const _CALLER: Location<'static> = *Location::caller();
+}
+
+#[test]
+fn location_const_file() {
+    const CALLER: &Location<'static> = Location::caller();
+    const FILE: &str = CALLER.file();
+    assert_eq!(FILE, file!());
+}
+
+#[test]
+fn location_const_line() {
+    const CALLER: &Location<'static> = Location::caller();
+    const LINE: u32 = CALLER.line();
+    assert_eq!(LINE, 21);
+}
+
+#[test]
+fn location_const_column() {
+    const CALLER: &Location<'static> = Location::caller();
+    const COLUMN: u32 = CALLER.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;
+}