parser: 'while parsing this or-pattern...'

src/libsyntax/parse/parser/pat.rs

@@ -81,7 +81,10 @@ impl<'a> Parser<'a> {
         let lo = first_pat.span;
         let mut pats = vec![first_pat];
         while self.eat_or_separator() {
-            let pat = self.parse_pat(None)?;
+            let pat = self.parse_pat(None).map_err(|mut err| {
+                err.span_label(lo, "while parsing this or-pattern staring here");
+                err
+            })?;
             self.maybe_recover_unexpected_comma(pat.span, top_level)?;
             pats.push(pat);
         }

src/test/ui/or-patterns/while-parsing-this-or-pattern.rs

@@ -0,0 +1,9 @@
+// Test the parser for the "while parsing this or-pattern..." label here.
+
+fn main() {
+    match Some(42) {
+        Some(42) | .=. => {} //~ ERROR expected pattern, found `.`
+        //~^ while parsing this or-pattern staring here
+        //~| NOTE expected pattern
+    }
+}

src/test/ui/or-patterns/while-parsing-this-or-pattern.stderr

@@ -0,0 +1,10 @@
+error: expected pattern, found `.`
+  --> $DIR/while-parsing-this-or-pattern.rs:5:20
+   |
+LL |         Some(42) | .=. => {}
+   |         --------   ^ expected pattern
+   |         |
+   |         while parsing this or-pattern staring here
+
+error: aborting due to previous error
+