fixes #3151 by skipping the lint instead of crashing

Author: PSeitz

clippy_lints/src/types.rs

@@ -1810,9 +1810,12 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitHasher {
 
                     let generics_suggestion_span = generics.span.substitute_dummy({
                         let pos = snippet_opt(cx, item.span.until(target.span()))
-                            .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)))
-                            .expect("failed to create span for type arguments");
-                        Span::new(pos, pos, item.span.data().ctxt)
+                            .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
+                        if let Some(pos) = pos {
+                            Span::new(pos, pos, item.span.data().ctxt)
+                        }else{
+                            return;
+                        }
                     });
 
                     let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);

tests/run-pass/ice-3151.rs

@@ -0,0 +1,13 @@
+#[derive(Clone)]
+pub struct HashMap<V, S> {
+    hash_builder: S,
+    table: RawTable<V>,
+}
+
+#[derive(Clone)]
+pub struct RawTable<V> {
+    size: usize,
+    val: V
+}
+
+fn main() {}