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, 6 insertions, 9 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 6c96692f719..bb1b7da7dba 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -21,10 +21,11 @@ use fold::{self, Folder};
 use parse::{self, parser, DirectoryOwnership};
 use parse::token;
 use ptr::P;
-use symbol::Symbol;
+use symbol::{keywords, Ident, Symbol};
 use util::small_vector::SmallVector;
 
 use std::collections::HashMap;
+use std::iter;
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::default::Default;
@@ -664,7 +665,6 @@ pub struct ExpansionData {
 pub struct ExtCtxt<'a> {
     pub parse_sess: &'a parse::ParseSess,
     pub ecfg: expand::ExpansionConfig<'a>,
-    pub crate_root: Option<&'static str>,
     pub root_path: PathBuf,
     pub resolver: &'a mut Resolver,
     pub resolve_err_count: usize,
@@ -680,7 +680,6 @@ impl<'a> ExtCtxt<'a> {
         ExtCtxt {
             parse_sess,
             ecfg,
-            crate_root: None,
             root_path: PathBuf::new(),
             resolver,
             resolve_err_count: 0,
@@ -822,12 +821,10 @@ impl<'a> ExtCtxt<'a> {
         ast::Ident::from_str(st)
     }
     pub fn std_path(&self, components: &[&str]) -> Vec<ast::Ident> {
-        let mut v = Vec::new();
-        if let Some(s) = self.crate_root {
-            v.push(self.ident_of(s));
-        }
-        v.extend(components.iter().map(|s| self.ident_of(s)));
-        v
+        let def_site = SyntaxContext::empty().apply_mark(self.current_expansion.mark);
+        iter::once(Ident { ctxt: def_site, ..keywords::DollarCrate.ident() })
+            .chain(components.iter().map(|s| self.ident_of(s)))
+            .collect()
     }
     pub fn name_of(&self, st: &str) -> ast::Name {
         Symbol::intern(st)