Avoid needless reexpansions.

1 files changed, 10 insertions, 5 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index edd38ea23e2..f6eb6f1da4f 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -13,7 +13,7 @@ pub use self::SyntaxExtension::*;
 use ast;
 use ast::{Name, PatKind};
 use attr::HasAttrs;
-use codemap::{self, CodeMap, ExpnInfo};
+use codemap::{self, CodeMap, ExpnInfo, Spanned, respan};
 use syntax_pos::{Span, ExpnId, NO_EXPANSION};
 use errors::DiagnosticBuilder;
 use ext;
@@ -805,8 +805,8 @@ impl<'a> ExtCtxt<'a> {
 /// Extract a string literal from the macro expanded version of `expr`,
 /// emitting `err_msg` if `expr` is not a string literal. This does not stop
 /// compilation on error, merely emits a non-fatal error and returns None.
-pub fn expr_to_string(cx: &mut ExtCtxt, expr: P<ast::Expr>, err_msg: &str)
-                      -> Option<(InternedString, ast::StrStyle)> {
+pub fn expr_to_spanned_string(cx: &mut ExtCtxt, expr: P<ast::Expr>, err_msg: &str)
+                              -> Option<Spanned<(InternedString, ast::StrStyle)>> {
     // Update `expr.span`'s expn_id now in case expr is an `include!` macro invocation.
     let expr = expr.map(|mut expr| {
         expr.span.expn_id = cx.backtrace;
@@ -817,7 +817,7 @@ pub fn expr_to_string(cx: &mut ExtCtxt, expr: P<ast::Expr>, err_msg: &str)
     let expr = cx.expander().fold_expr(expr);
     match expr.node {
         ast::ExprKind::Lit(ref l) => match l.node {
-            ast::LitKind::Str(ref s, style) => return Some(((*s).clone(), style)),
+            ast::LitKind::Str(ref s, style) => return Some(respan(expr.span, (s.clone(), style))),
             _ => cx.span_err(l.span, err_msg)
         },
         _ => cx.span_err(expr.span, err_msg)
@@ -825,6 +825,11 @@ pub fn expr_to_string(cx: &mut ExtCtxt, expr: P<ast::Expr>, err_msg: &str)
     None
 }
 
+pub fn expr_to_string(cx: &mut ExtCtxt, expr: P<ast::Expr>, err_msg: &str)
+                      -> Option<(InternedString, ast::StrStyle)> {
+    expr_to_spanned_string(cx, expr, err_msg).map(|s| s.node)
+}
+
 /// Non-fatally assert that `tts` is empty. Note that this function
 /// returns even when `tts` is non-empty, macros that *need* to stop
 /// compilation should call
@@ -851,7 +856,7 @@ pub fn get_single_str_from_tts(cx: &mut ExtCtxt,
         cx.span_err(sp, &format!("{} takes 1 argument", name));
         return None
     }
-    let ret = cx.expander().fold_expr(panictry!(p.parse_expr()));
+    let ret = panictry!(p.parse_expr());
     if p.token != token::Eof {
         cx.span_err(sp, &format!("{} takes 1 argument", name));
     }