Rollup merge of rust-lang#65294 - varkor:lint-inline-prototype, r=matthewjasper

Lint ignored `#[inline]` on function prototypes

Fixes rust-lang#51280.

- Adds a `unused_attribute` lint for `#[inline]` on function prototypes.
- As a consequence, foreign items, impl items and trait items now have their attributes checked, which could cause some code to no longer compile (it was previously erroneously ignored).

Author: Centril

Cargo.lock

@@ -150,9 +150,9 @@ dependencies = [
 
 [[package]]
 name = "bitflags"
-version = "1.1.0"
+version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3d155346769a6855b86399e9bc3814ab343cd3d62c7e985113d46a0ec3c281fd"
+checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 
 [[package]]
 name = "blake2-rfc"

src/librustc/Cargo.toml

@@ -11,7 +11,7 @@ doctest = false
 
 [dependencies]
 arena = { path = "../libarena" }
-bitflags = "1.0"
+bitflags = "1.2.1"
 fmt_macros = { path = "../libfmt_macros" }
 graphviz = { path = "../libgraphviz" }
 jobserver = "0.1"

src/librustc/error_codes.rs

@@ -2219,7 +2219,7 @@ rejected in your own crates.
 "##,
 
 E0736: r##"
-#[track_caller] and #[naked] cannot be applied to the same function.
+`#[track_caller]` and `#[naked]` cannot both be applied to the same function.
 
 Erroneous code example:
 
@@ -2237,6 +2237,57 @@ 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
 "##,
 
+E0738: r##"
+`#[track_caller]` cannot be used in traits yet. This is due to limitations in
+the compiler which are likely to be temporary. See [RFC 2091] for details on
+this and other restrictions.
+
+Erroneous example with a trait method implementation:
+
+```compile_fail,E0738
+#![feature(track_caller)]
+
+trait Foo {
+    fn bar(&self);
+}
+
+impl Foo for u64 {
+    #[track_caller]
+    fn bar(&self) {}
+}
+```
+
+Erroneous example with a blanket trait method implementation:
+
+```compile_fail,E0738
+#![feature(track_caller)]
+
+trait Foo {
+    #[track_caller]
+    fn bar(&self) {}
+    fn baz(&self);
+}
+```
+
+Erroneous example with a trait method declaration:
+
+```compile_fail,E0738
+#![feature(track_caller)]
+
+trait Foo {
+    fn bar(&self) {}
+
+    #[track_caller]
+    fn baz(&self);
+}
+```
+
+Note that while the compiler may be able to support the attribute in traits in
+the future, [RFC 2091] prohibits their implementation without a follow-up RFC.
+
+[RFC 2091]: https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md
+"##,
+
 ;
 //  E0006, // merged with E0005
 //  E0101, // replaced with E0282