begin crate-relative paths with crate

src/libsyntax/ext/build.rs

@@ -319,14 +319,8 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                 types: Vec<P<ast::Ty>>,
                 bindings: Vec<ast::TypeBinding> )
                 -> ast::Path {
-        use syntax::parse::token;
-
         let last_identifier = idents.pop().unwrap();
         let mut segments: Vec<ast::PathSegment> = Vec::new();
-        if global &&
-           !idents.first().map_or(false, |&ident| token::Ident(ident).is_path_segment_keyword()) {
-            segments.push(ast::PathSegment::crate_root(span));
-        }
 
         segments.extend(idents.into_iter().map(|i| ast::PathSegment::from_ident(i, span)));
         let parameters = if !lifetimes.is_empty() || !types.is_empty() || !bindings.is_empty() {
@@ -335,7 +329,9 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             None
         };
         segments.push(ast::PathSegment { identifier: last_identifier, span, parameters });
-        ast::Path { span, segments }
+        let path = ast::Path { span, segments };
+
+        if global { path.default_to_global() } else { path }
     }
 
     /// Constructs a qualified path.

src/libsyntax/test.rs

@@ -733,9 +733,12 @@ fn mk_test_desc_and_fn_rec(cx: &TestCtxt, test: &Test) -> P<ast::Expr> {
              field("should_panic", fail_expr),
              field("allow_fail", allow_fail_expr)]);
 
-
-    let mut visible_path = match cx.toplevel_reexport {
-        Some(id) => vec![id],
+    let mut visible_path = vec![];
+    if cx.features.extern_absolute_paths {
+        visible_path.push(keywords::Crate.ident());
+    }
+    match cx.toplevel_reexport {
+        Some(id) => visible_path.push(id),
         None => {
             let diag = cx.span_diagnostic;
             diag.bug("expected to find top-level re-export name, but found None");

src/test/run-pass/rfc-2126-extern-absolute-paths/test.rs

@@ -0,0 +1,21 @@
+// Copyright 2017 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.
+
+// Check that `#[test]` works with extern-absolute-paths enabled.
+//
+// Regression test for #47075.
+
+// compile-flags: --test
+
+#![feature(extern_absolute_paths)]
+
+#[test]
+fn test() {
+}