fix panic on ellipsis in pattern

1 files changed, 10 insertions, 3 deletions

diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index 79abe55ce..0679ffa1e 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -650,6 +650,7 @@ impl ExprCollector<'_> {
             ast::Pat::SlicePat(p) => {
                 let SlicePatComponents { prefix, slice, suffix } = p.components();
 
+                // FIXME properly handle `DotDotPat`
                 Pat::Slice {
                     prefix: prefix.into_iter().map(|p| self.collect_pat(p)).collect(),
                     slice: slice.map(|p| self.collect_pat(p)),
@@ -666,9 +667,15 @@ impl ExprCollector<'_> {
                     Pat::Missing
                 }
             }
-            ast::Pat::DotDotPat(_) => unreachable!(
-                "`DotDotPat` requires special handling and should not be mapped to a Pat."
-            ),
+            ast::Pat::DotDotPat(_) => {
+                // `DotDotPat` requires special handling and should not be mapped
+                // to a Pat. Here we are using `Pat::Missing` as a fallback for
+                // when `DotDotPat` is mapped to `Pat`, which can easily happen
+                // when the source code being analyzed has a malformed pattern
+                // which includes `..` in a place where it isn't valid.
+
+                Pat::Missing
+            }
             // FIXME: implement
             ast::Pat::BoxPat(_) | ast::Pat::RangePat(_) | ast::Pat::MacroPat(_) => Pat::Missing,
         };