Auto merge of #40346 - jseyfried:path_and_tokenstream_attr, r=nrc

`TokenStream`-based attributes, paths in attribute and derive macro invocations

This PR
 - refactors `Attribute` to use  `Path` and `TokenStream` instead of `MetaItem`.
 - supports macro invocation paths for attribute procedural macros.
   - e.g. `#[::foo::attr_macro] struct S;`, `#[cfg_attr(all(), foo::attr_macro)] struct S;`
 - supports macro invocation paths for derive procedural macros.
   - e.g. `#[derive(foo::Bar, super::Baz)] struct S;`
 - supports arbitrary tokens as arguments to attribute procedural macros.
   - e.g. `#[foo::attr_macro arbitrary + tokens] struct S;`
 - supports using arbitrary tokens in "inert attributes" with derive procedural macros.
   - e.g. `#[derive(Foo)] struct S(#[inert arbitrary + tokens] i32);`
where `#[proc_macro_derive(Foo, attributes(inert))]`

r? @nrc

src/test/compile-fail/macro-attribute.rs

@@ -0,0 +1,12 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#[doc = $not_there] //~ error: unexpected token: `$`
+fn main() { }

src/test/compile-fail/macro-with-seps-err-msg.rs

@@ -14,4 +14,5 @@ fn main() {
     globnar::brotz!(); //~ ERROR non-ident macro paths are experimental
     ::foo!(); //~ ERROR non-ident macro paths are experimental
     foo::<T>!(); //~ ERROR type parameters are not allowed on macros
+    #[derive(foo::Bar)] struct T; //~ ERROR non-ident macro paths are experimental
 }

src/test/compile-fail/malformed-derive-entry.rs

@@ -9,11 +9,11 @@
 // except according to those terms.
 
 #[derive(Copy(Bad))]
-//~^ ERROR malformed `derive` entry
+//~^ ERROR expected one of `)`, `,`, or `::`, found `(`
 struct Test1;
 
 #[derive(Copy="bad")]
-//~^ ERROR malformed `derive` entry
+//~^ ERROR expected one of `)`, `,`, or `::`, found `=`
 struct Test2;
 
 #[derive()]

src/test/compile-fail/suffixed-literal-meta.rs

@@ -0,0 +1,25 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(attr_literals)]
+
+#[path = 1usize] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1u8] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1u16] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1u32] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1u64] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1isize] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1i8] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1i16] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1i32] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1i64] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1.0f32] //~ ERROR: suffixed literals are not allowed in attributes
+#[path = 1.0f64] //~ ERROR: suffixed literals are not allowed in attributes
+fn main() { }