Fix regression on include!(line!()).

src/libsyntax/ext/base.rs

@@ -695,7 +695,7 @@ impl<'a> ExtCtxt<'a> {
     /// Returns span for the macro which originally caused the current expansion to happen.
     ///
     /// Stops backtracing at include! boundary.
-    pub fn expansion_cause(&self) -> Span {
+    pub fn expansion_cause(&self) -> Option<Span> {
         let mut ctxt = self.backtrace();
         let mut last_macro = None;
         loop {
@@ -711,7 +711,7 @@ impl<'a> ExtCtxt<'a> {
                 break
             }
         }
-        last_macro.expect("missing expansion backtrace")
+        last_macro
     }
 
     pub fn struct_span_warn(&self,

src/libsyntax/ext/source_util.rs

@@ -35,7 +35,7 @@ pub fn expand_line(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
                    -> Box<base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "line!");
 
-    let topmost = cx.expansion_cause();
+    let topmost = cx.expansion_cause().unwrap_or(sp);
     let loc = cx.codemap().lookup_char_pos(topmost.lo);
 
     base::MacEager::expr(cx.expr_u32(topmost, loc.line as u32))
@@ -46,7 +46,7 @@ pub fn expand_column(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
                   -> Box<base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "column!");
 
-    let topmost = cx.expansion_cause();
+    let topmost = cx.expansion_cause().unwrap_or(sp);
     let loc = cx.codemap().lookup_char_pos(topmost.lo);
 
     base::MacEager::expr(cx.expr_u32(topmost, loc.col.to_usize() as u32))
@@ -59,7 +59,7 @@ pub fn expand_file(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
                    -> Box<base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "file!");
 
-    let topmost = cx.expansion_cause();
+    let topmost = cx.expansion_cause().unwrap_or(sp);
     let loc = cx.codemap().lookup_char_pos(topmost.lo);
     base::MacEager::expr(cx.expr_str(topmost, Symbol::intern(&loc.file.name)))
 }

src/test/compile-fail/issue-41776.rs

@@ -0,0 +1,13 @@
+// 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.
+
+fn main() {
+    include!(line!()); //~ ERROR argument must be a string literal
+}