2 files changed, 16 insertions, 7 deletions

diff --git a/src/tree/file_builder.rs b/src/tree/file_builder.rs
index 37bd5b2c8..35702ddd7 100644
--- a/src/tree/file_builder.rs
+++ b/src/tree/file_builder.rs
@@ -48,7 +48,9 @@ impl Sink for FileBuilder {
     }
 
     fn finish_internal(&mut self) {
-        let (id, _) = self.in_progress.pop().unwrap();
+        let (id, _) = self.in_progress.pop().expect(
+            "trying to complete a node, but there are no in-progress nodes"
+        );
         if !self.in_progress.is_empty() {
             self.add_len(id);
         }
@@ -77,8 +79,8 @@ impl FileBuilder {
             self.in_progress.iter().map(|&(idx, _)| self.nodes[idx].kind)
                 .collect::<Vec<_>>()
         );
-        assert!(
-            self.pos == (self.text.len() as u32).into(),
+        assert_eq!(
+            self.pos, (self.text.len() as u32).into(),
             "nodes in FileBuilder do not cover the whole file"
         );
         File {
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index d8f843737..3315b926e 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -10,17 +10,24 @@ pub use self::file_builder::{FileBuilder, Sink};
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct SyntaxKind(pub(crate) u32);
 
-pub(crate) const EOF: SyntaxKind = SyntaxKind(10000);
+pub(crate) const EOF: SyntaxKind = SyntaxKind(!0);
 pub(crate) const EOF_INFO: SyntaxInfo = SyntaxInfo {
     name: "EOF"
 };
 
+pub(crate) const TOMBSTONE: SyntaxKind = SyntaxKind(!0 - 1);
+pub(crate) const TOMBSTONE_INFO: SyntaxInfo = SyntaxInfo {
+    name: "TOMBSTONE"
+};
+
+
 impl SyntaxKind {
     fn info(self) -> &'static SyntaxInfo {
-        if self == EOF {
-            return &EOF_INFO;
+        match self {
+            EOF => &EOF_INFO,
+            TOMBSTONE => &TOMBSTONE_INFO,
+            _ => syntax_info(self),
         }
-        syntax_info(self)
     }
 }