1 files changed, 42 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/parser/src/token_set.rs b/src/tools/rust-analyzer/crates/parser/src/token_set.rs
new file mode 100644
index 000000000..cd4894c1e
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/parser/src/token_set.rs
@@ -0,0 +1,42 @@
+//! A bit-set of `SyntaxKind`s.
+
+use crate::SyntaxKind;
+
+/// A bit-set of `SyntaxKind`s
+#[derive(Clone, Copy)]
+pub(crate) struct TokenSet(u128);
+
+impl TokenSet {
+    pub(crate) const EMPTY: TokenSet = TokenSet(0);
+
+    pub(crate) const fn new(kinds: &[SyntaxKind]) -> TokenSet {
+        let mut res = 0u128;
+        let mut i = 0;
+        while i < kinds.len() {
+            res |= mask(kinds[i]);
+            i += 1;
+        }
+        TokenSet(res)
+    }
+
+    pub(crate) const fn union(self, other: TokenSet) -> TokenSet {
+        TokenSet(self.0 | other.0)
+    }
+
+    pub(crate) const fn contains(&self, kind: SyntaxKind) -> bool {
+        self.0 & mask(kind) != 0
+    }
+}
+
+const fn mask(kind: SyntaxKind) -> u128 {
+    1u128 << (kind as usize)
+}
+
+#[test]
+fn token_set_works_for_tokens() {
+    use crate::SyntaxKind::*;
+    let ts = TokenSet::new(&[EOF, SHEBANG]);
+    assert!(ts.contains(EOF));
+    assert!(ts.contains(SHEBANG));
+    assert!(!ts.contains(PLUS));
+}