Allow #[track_caller] in traits.

The codegen implementation already works for this, so we're:

* propagating track_caller attr from trait def to impl
* relaxing errors
* adding tests

Approved in a recent lang team meeting:
https://github.com/rust-lang/lang-team/blob/master/minutes/2020-01-09.md

src/test/ui/rfc-2091-track-caller/error-extern-fn.rs

@@ -0,0 +1,9 @@
+#![feature(track_caller)]
+#![allow(dead_code)]
+
+extern "Rust" {
+    #[track_caller] //~ ERROR: `#[track_caller]` is not supported on foreign functions
+    fn bar();
+}
+
+fn main() {}

src/test/ui/rfc-2091-track-caller/error-extern-fn.stderr

@@ -1,5 +1,5 @@
-error[E0738]: `#[track_caller]` may not be used on trait methods
-  --> $DIR/error-with-trait-decl.rs:4:5
+error[E0738]: `#[track_caller]` is not supported on foreign functions
+  --> $DIR/error-extern-fn.rs:5:5
    |
 LL |     #[track_caller]
    |     ^^^^^^^^^^^^^^^

src/test/ui/rfc-2091-track-caller/error-with-trait-decl.rs

@@ -1,12 +0,0 @@
-#![feature(track_caller)]
-
-trait Trait {
-    #[track_caller] //~ ERROR: `#[track_caller]` may not be used on trait methods
-    fn unwrap(&self);
-}
-
-impl Trait for u64 {
-    fn unwrap(&self) {}
-}
-
-fn main() {}

src/test/ui/rfc-2091-track-caller/error-with-trait-default-impl.rs

@@ -1,8 +0,0 @@
-#![feature(track_caller)]
-
-trait Trait {
-    #[track_caller] //~ ERROR: `#[track_caller]` may not be used on trait methods
-    fn unwrap(&self) {}
-}
-
-fn main() {}

src/test/ui/rfc-2091-track-caller/error-with-trait-default-impl.stderr

@@ -1,9 +0,0 @@
-error[E0738]: `#[track_caller]` may not be used on trait methods
-  --> $DIR/error-with-trait-default-impl.rs:4:5
-   |
-LL |     #[track_caller]
-   |     ^^^^^^^^^^^^^^^
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0738`.

src/test/ui/rfc-2091-track-caller/error-with-trait-fn-impl.rs

@@ -1,21 +0,0 @@
-// check-fail
-
-#![feature(track_caller)]
-
-trait Trait {
-    fn unwrap(&self);
-}
-
-impl Trait for u64 {
-    #[track_caller] //~ ERROR: `#[track_caller]` may not be used on trait methods
-    fn unwrap(&self) {}
-}
-
-struct S;
-
-impl S {
-    #[track_caller] // ok
-    fn foo() {}
-}
-
-fn main() {}

src/test/ui/rfc-2091-track-caller/error-with-trait-fn-impl.stderr

@@ -1,9 +0,0 @@
-error[E0738]: `#[track_caller]` may not be used on trait methods
-  --> $DIR/error-with-trait-fn-impl.rs:10:5
-   |
-LL |     #[track_caller]
-   |     ^^^^^^^^^^^^^^^
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0738`.

src/test/ui/rfc-2091-track-caller/tracked-fn-ptr-with-arg.rs

@@ -14,6 +14,49 @@ fn tracked_unit(_: ()) {
     assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
 }
 
+trait Trait {
+    fn trait_tracked_unit(_: ());
+}
+
+impl Trait for () {
+    #[track_caller]
+    fn trait_tracked_unit(_: ()) {
+        let expected_line = line!() - 1;
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
+    }
+}
+
+trait TrackedTrait {
+    #[track_caller]
+    fn trait_tracked_unit_default(_: ()) {
+        let expected_line = line!() - 1;
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
+    }
+}
+
+impl TrackedTrait for () {}
+
+trait BlanketTrackedTrait {
+    #[track_caller]
+    fn tracked_blanket(_: ());
+}
+
+impl BlanketTrackedTrait for () {
+    fn tracked_blanket(_: ()) {
+        let expected_line = line!() - 1;
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
+    }
+}
+
 fn main() {
     pass_to_ptr_call(tracked_unit, ());
+    pass_to_ptr_call(<() as Trait>::trait_tracked_unit, ());
+    pass_to_ptr_call(<() as TrackedTrait>::trait_tracked_unit_default, ());
+    pass_to_ptr_call(<() as BlanketTrackedTrait>::tracked_blanket, ());
 }

src/test/ui/rfc-2091-track-caller/tracked-fn-ptr.rs

@@ -14,6 +14,49 @@ fn tracked() {
     assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
 }
 
+trait Trait {
+    fn trait_tracked();
+}
+
+impl Trait for () {
+    #[track_caller]
+    fn trait_tracked() {
+        let expected_line = line!() - 1;
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
+    }
+}
+
+trait TrackedTrait {
+    #[track_caller]
+    fn trait_tracked_default() {
+        let expected_line = line!() - 1;
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
+    }
+}
+
+impl TrackedTrait for () {}
+
+trait TraitBlanketTracked {
+    #[track_caller]
+    fn tracked_blanket();
+}
+
+impl TraitBlanketTracked for () {
+    fn tracked_blanket() {
+        let expected_line = line!() - 1;
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_eq!(location.line(), expected_line, "call shims report location as fn definition");
+    }
+}
+
 fn main() {
     ptr_call(tracked);
+    ptr_call(<() as Trait>::trait_tracked);
+    ptr_call(<() as TrackedTrait>::trait_tracked_default);
+    ptr_call(<() as TraitBlanketTracked>::tracked_blanket);
 }

src/test/ui/rfc-2091-track-caller/tracked-trait-impls.rs

@@ -0,0 +1,79 @@
+// run-pass
+
+#![feature(track_caller)]
+
+macro_rules! assert_expansion_site_is_tracked {
+    () => {{
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        assert_ne!(location.line(), line!(), "line should be outside this fn");
+    }}
+}
+
+trait Tracked {
+    fn local_tracked(&self);
+
+    #[track_caller]
+    fn blanket_tracked(&self);
+
+    #[track_caller]
+    fn default_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+}
+
+impl Tracked for () {
+    #[track_caller]
+    fn local_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+
+    fn blanket_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+}
+
+impl Tracked for bool {
+    #[track_caller]
+    fn local_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+
+    fn blanket_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+
+    fn default_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+}
+
+impl Tracked for u8 {
+    #[track_caller]
+    fn local_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+
+    fn blanket_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+
+    #[track_caller]
+    fn default_tracked(&self) {
+        assert_expansion_site_is_tracked!();
+    }
+}
+
+fn main() {
+    ().local_tracked();
+    ().default_tracked();
+    ().blanket_tracked();
+
+    true.local_tracked();
+    true.default_tracked();
+    true.blanket_tracked();
+
+    0u8.local_tracked();
+    0u8.default_tracked();
+    0u8.blanket_tracked();
+}