Auto merge of #1109 - RalfJung:track-caller, r=RalfJung

add caller_location tests to Miri

The CTFE implementation seems to also work fine in Miri -- thanks a lot @anp :)

tests/run-pass/track-caller-attribute.rs

@@ -0,0 +1,54 @@
+#![feature(track_caller, core_intrinsics)]
+
+use std::panic::Location;
+
+#[track_caller]
+fn tracked() -> &'static Location<'static> {
+    Location::caller() // most importantly, we never get line 7
+}
+
+fn nested_intrinsic() -> &'static Location<'static> {
+    Location::caller()
+}
+
+fn nested_tracked() -> &'static Location<'static> {
+    tracked()
+}
+
+macro_rules! caller_location_from_macro {
+    () => (core::panic::Location::caller());
+}
+
+fn main() {
+    let location = Location::caller();
+    assert_eq!(location.file(), file!());
+    assert_eq!(location.line(), 23);
+    assert_eq!(location.column(), 20);
+
+    let tracked = tracked();
+    assert_eq!(tracked.file(), file!());
+    assert_eq!(tracked.line(), 28);
+    assert_eq!(tracked.column(), 19);
+
+    let nested = nested_intrinsic();
+    assert_eq!(nested.file(), file!());
+    assert_eq!(nested.line(), 11);
+    assert_eq!(nested.column(), 5);
+
+    let contained = nested_tracked();
+    assert_eq!(contained.file(), file!());
+    assert_eq!(contained.line(), 15);
+    assert_eq!(contained.column(), 5);
+
+    // `Location::caller()` in a macro should behave similarly to `file!` and `line!`,
+    // i.e. point to where the macro was invoked, instead of the macro itself.
+    let inmacro = caller_location_from_macro!();
+    assert_eq!(inmacro.file(), file!());
+    assert_eq!(inmacro.line(), 45);
+    assert_eq!(inmacro.column(), 19);
+
+    let intrinsic = core::intrinsics::caller_location();
+    assert_eq!(intrinsic.file(), file!());
+    assert_eq!(intrinsic.line(), 50);
+    assert_eq!(intrinsic.column(), 21);
+}