rustdoc: tolerate PatKind::Missing in rustc_ast_pretty

Author: el-ev

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1725,7 +1725,7 @@ impl<'a> State<'a> {
         self.ann.pre(self, AnnNode::Pat(pat));
         /* Pat isn't normalized, but the beauty of it is that it doesn't matter */
         match &pat.kind {
-            PatKind::Missing => unreachable!(),
+            PatKind::Missing => {}
             PatKind::Wild => self.word("_"),
             PatKind::Never => self.word("!"),
             PatKind::Ident(BindingMode(by_ref, mutbl), ident, sub) => {

tests/rustdoc/macro-expansion/missing-par-ice-150154.rs

@@ -0,0 +1,18 @@
+// Ensure rustdoc does not ICE When expanding a macro that
+// generates a `PatKind::Missing` pattern.
+
+//@ compile-flags: -Zunstable-options --generate-macro-expansion
+
+#![crate_name = "foo"]
+
+//@ has 'src/foo/missing-par-ice-150154.rs.html'
+
+macro_rules! foo {
+    () => {
+        fn(())
+    }
+}
+
+fn bar() {
+    let _: foo!();
+}