Be smarter about finding the span for .. in patterns

Fixes #1319

src/patterns.rs

@@ -210,8 +210,19 @@ fn rewrite_tuple_pat(pats: &[ptr::P<ast::Pat>],
     let mut pat_vec: Vec<_> = pats.into_iter().map(|x| TuplePatField::Pat(x)).collect();
 
     if let Some(pos) = dotdot_pos {
-        let snippet = context.snippet(span);
-        let lo = span.lo + BytePos(snippet.find_uncommented("..").unwrap() as u32);
+        let prev = if pos == 0 {
+            span.lo
+        } else {
+            pats[pos - 1].span().hi
+        };
+        let next = if pos + 1 >= pats.len() {
+            span.hi
+        } else {
+            pats[pos + 1].span().lo
+        };
+        let dot_span = codemap::mk_sp(prev, next);
+        let snippet = context.snippet(dot_span);
+        let lo = dot_span.lo + BytePos(snippet.find_uncommented("..").unwrap() as u32);
         let span = Span {
             lo: lo,
             // 2 == "..".len()

tests/source/pattern.rs

@@ -38,3 +38,8 @@ impl<'a,'b> ResolveGeneratedContentFragmentMutator<'a,'b> {
                 )
             ) => {}}}
 }
+
+fn issue_1319() {
+    if let (Event { .. }, .. ) = ev_state {}
+}
+

tests/target/pattern.rs

@@ -41,3 +41,7 @@ impl<'a, 'b> ResolveGeneratedContentFragmentMutator<'a, 'b> {
         }
     }
 }
+
+fn issue_1319() {
+    if let (Event { .. }, ..) = ev_state {}
+}