move all parsing related bits to a separate module

crates/ra_syntax/src/parsing/token_set.rs

@@ -0,0 +1,41 @@
+use crate::SyntaxKind;
+
+#[derive(Clone, Copy)]
+pub(crate) struct TokenSet(u128);
+
+impl TokenSet {
+    pub(crate) const fn empty() -> TokenSet {
+        TokenSet(0)
+    }
+
+    pub(crate) const fn singleton(kind: SyntaxKind) -> TokenSet {
+        TokenSet(mask(kind))
+    }
+
+    pub(crate) const fn union(self, other: TokenSet) -> TokenSet {
+        TokenSet(self.0 | other.0)
+    }
+
+    pub(crate) fn contains(&self, kind: SyntaxKind) -> bool {
+        self.0 & mask(kind) != 0
+    }
+}
+
+const fn mask(kind: SyntaxKind) -> u128 {
+    1u128 << (kind as usize)
+}
+
+#[macro_export]
+macro_rules! token_set {
+    ($($t:ident),*) => { TokenSet::empty()$(.union(TokenSet::singleton($t)))* };
+    ($($t:ident),* ,) => { token_set!($($t),*) };
+}
+
+#[test]
+fn token_set_works_for_tokens() {
+    use crate::SyntaxKind::*;
+    let ts = token_set! { EOF, SHEBANG };
+    assert!(ts.contains(EOF));
+    assert!(ts.contains(SHEBANG));
+    assert!(!ts.contains(PLUS));
+}