Rollup merge of #65037 - anp:track-caller, r=oli-obk

`#[track_caller]` feature gate (RFC 2091 1/N)

RFC text: https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md
Tracking issue: https://github.com/rust-lang/rust/issues/47809

I started with @ayosec's commit to add the feature gate with tests and rebased it onto current master. I fixed up some tidy lints and added a test.

src/librustc/error_codes.rs

@@ -2120,6 +2120,25 @@ These attributes are meant to only be used by the standard library and are
 rejected in your own crates.
 "##,
 
+E0736: r##"
+#[track_caller] and #[naked] cannot be applied to the same function.
+
+Erroneous code example:
+
+```compile_fail,E0736
+#![feature(track_caller)]
+
+#[naked]
+#[track_caller]
+fn foo() {}
+```
+
+This is primarily due to ABI incompatibilities between the two attributes.
+See [RFC 2091] for details on this and other limitations.
+
+[RFC 2091]: https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md
+"##,
+
 ;
 //  E0006, // merged with E0005
 //  E0101, // replaced with E0282
@@ -2179,4 +2198,5 @@ rejected in your own crates.
     E0726, // non-explicit (not `'_`) elided lifetime in unsupported position
     E0727, // `async` generators are not yet supported
     E0728, // `await` must be in an `async` function or block
+    E0739, // invalid track_caller application/syntax
 }

src/librustc/hir/check_attr.rs

@@ -11,7 +11,7 @@ use crate::ty::TyCtxt;
 use crate::ty::query::Providers;
 
 use std::fmt::{self, Display};
-use syntax::symbol::sym;
+use syntax::{attr, symbol::sym};
 use syntax_pos::Span;
 
 #[derive(Copy, Clone, PartialEq)]
@@ -103,6 +103,8 @@ impl CheckAttrVisitor<'tcx> {
                 self.check_marker(attr, item, target)
             } else if attr.check_name(sym::target_feature) {
                 self.check_target_feature(attr, item, target)
+            } else if attr.check_name(sym::track_caller) {
+                self.check_track_caller(attr, &item, target)
             } else {
                 true
             };
@@ -135,6 +137,32 @@ impl CheckAttrVisitor<'tcx> {
         }
     }
 
+    /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
+    fn check_track_caller(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) -> bool {
+        if target != Target::Fn {
+            struct_span_err!(
+                self.tcx.sess,
+                attr.span,
+                E0739,
+                "attribute should be applied to function"
+            )
+            .span_label(item.span, "not a function")
+            .emit();
+            false
+        } else if attr::contains_name(&item.attrs, sym::naked) {
+            struct_span_err!(
+                self.tcx.sess,
+                attr.span,
+                E0736,
+                "cannot use `#[track_caller]` with `#[naked]`",
+            )
+            .emit();
+            false
+        } else {
+            true
+        }
+    }
+
     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
     fn check_non_exhaustive(
         &self,

src/librustc/hir/mod.rs

@@ -2734,7 +2734,9 @@ bitflags! {
         const USED                      = 1 << 9;
         /// #[ffi_returns_twice], indicates that an extern function can return
         /// multiple times
-        const FFI_RETURNS_TWICE = 1 << 10;
+        const FFI_RETURNS_TWICE         = 1 << 10;
+        /// #[track_caller]: allow access to the caller location
+        const TRACK_CALLER              = 1 << 11;
     }
 }