Rollup merge of rust-lang#48083 - jseyfried:improve_tuple_struct_field_access_hygiene, r=petrochenkov

Improve tuple struct field access hygiene

Fixes rust-lang#47312 by fixing a span bug.
r? @nrc

Author: Manishearth

src/libsyntax/parse/parser.rs

@@ -2630,8 +2630,7 @@ impl<'a> Parser<'a> {
                     // A tuple index may not have a suffix
                     self.expect_no_suffix(sp, "tuple index", suf);
 
-                    let dot_span = self.prev_span;
-                    hi = self.span;
+                    let idx_span = self.span;
                     self.bump();
 
                     let invalid_msg = "invalid tuple or struct index";
@@ -2646,9 +2645,8 @@ impl<'a> Parser<'a> {
                                                     n.to_string());
                                 err.emit();
                             }
-                            let id = respan(dot_span.to(hi), n);
-                            let field = self.mk_tup_field(e, id);
-                            e = self.mk_expr(lo.to(hi), field, ThinVec::new());
+                            let field = self.mk_tup_field(e, respan(idx_span, n));
+                            e = self.mk_expr(lo.to(idx_span), field, ThinVec::new());
                         }
                         None => {
                             let prev_span = self.prev_span;

src/test/run-pass/hygiene/issue-47312.rs

@@ -0,0 +1,30 @@
+// 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.
+
+// ignore-pretty pretty-printing is unhygienic
+
+#![feature(decl_macro)]
+#![allow(unused)]
+
+mod foo {
+    pub macro m($s:tt, $i:tt) {
+        $s.$i
+    }
+}
+
+mod bar {
+    struct S(i32);
+    fn f() {
+        let s = S(0);
+        ::foo::m!(s, 0);
+    }
+}
+
+fn main() {}