Auto merge of #46550 - jseyfried:cleanup_builtin_hygiene, r=nrc

macros: hygienize use of `core`/`std` in builtin macros

Today, if a builtin macro wants to access an item from `core` or `std` (depending `#![no_std]`), it generates `::core::path::to::item` or `::std::path::to::item` respectively (c.f. `fn std_path()` in `libsyntax/ext/base.rs`).

This PR refactors the builtin macros to instead always emit `$crate::path::to::item` here. That is, the def site of builtin macros is taken to be in `extern crate core;` or `extern crate std;`. Since builtin macros are macros 1.0 (i.e. mostly unhygienic), changing the def site can only effect the resolution of `$crate`.

r? @nrc

1 files changed, 3 insertions, 2 deletions

diff --git a/src/libsyntax_ext/deriving/clone.rs b/src/libsyntax_ext/deriving/clone.rs
index 5d93c2a5f72..35def632fc1 100644
--- a/src/libsyntax_ext/deriving/clone.rs
+++ b/src/libsyntax_ext/deriving/clone.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use deriving::path_std;
 use deriving::generic::*;
 use deriving::generic::ty::*;
 
@@ -55,7 +56,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt,
                     }));
                 }
                 ItemKind::Union(..) => {
-                    bounds = vec![Literal(path_std!(cx, core::marker::Copy))];
+                    bounds = vec![Literal(path_std!(cx, marker::Copy))];
                     is_shallow = true;
                     substructure = combine_substructure(Box::new(|c, s, sub| {
                         cs_clone_shallow("Clone", c, s, sub, true)
@@ -79,7 +80,7 @@ pub fn expand_deriving_clone(cx: &mut ExtCtxt,
     let trait_def = TraitDef {
         span,
         attributes: Vec::new(),
-        path: path_std!(cx, core::clone::Clone),
+        path: path_std!(cx, clone::Clone),
         additional_bounds: bounds,
         generics: LifetimeBounds::empty(),
         is_unsafe: false,