Add error message specific to \<carriage return>.

This can crop-up with a misconfigured editor or an unexpected
interaction between version control and certain operating systems.

Closes #11669.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 35d56440b50..01a66243a96 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -806,6 +806,13 @@ impl<'a> StringReader<'a> {
                                     if ascii_only { "unknown byte escape" }
                                     else { "unknown character escape" },
                                     c);
+                                if e == '\r' {
+                                    let sp = codemap::mk_sp(escaped_pos, last_pos);
+                                    self.span_diagnostic.span_help(
+                                        sp,
+                                        "this is an isolated carriage return; consider checking \
+                                         your editor and version control settings.")
+                                }
                                 false
                             }
                         }