reorganize

src/parser_api.rs

@@ -0,0 +1,164 @@
+use {
+    parser_impl::ParserImpl,
+    SyntaxKind::{self, ERROR},
+};
+
+pub(crate) struct TokenSet {
+    pub tokens: &'static [SyntaxKind],
+}
+
+impl TokenSet {
+    pub fn contains(&self, kind: SyntaxKind) -> bool {
+        self.tokens.contains(&kind)
+    }
+}
+
+#[macro_export]
+macro_rules! token_set {
+    ($($t:ident),*) => {
+        TokenSet {
+            tokens: &[$($t),*],
+        }
+    };
+
+    ($($t:ident),* ,) => {
+        token_set!($($t),*)
+    };
+}
+
+/// `Parser` struct provides the low-level API for
+/// navigating through the stream of tokens and
+/// constructing the parse tree. The actual parsing
+/// happens in the `grammar` module.
+///
+/// However, the result of this `Parser` is not a real
+/// tree, but rather a flat stream of events of the form
+/// "start expression, consume number literal,
+/// finish expression". See `Event` docs for more.
+pub(crate) struct Parser<'t>(pub(super) ParserImpl<'t>);
+
+impl<'t> Parser<'t> {
+    /// Returns the kind of the current token.
+    /// If parser has already reached the end of input,
+    /// the special `EOF` kind is returned.
+    pub(crate) fn current(&self) -> SyntaxKind {
+        self.nth(0)
+    }
+
+    /// Lookahead operation: returns the kind of the next nth
+    /// token.
+    pub(crate) fn nth(&self, n: u32) -> SyntaxKind {
+        self.0.nth(n)
+    }
+
+    /// Checks if the current token is `kind`.
+    pub(crate) fn at(&self, kind: SyntaxKind) -> bool {
+        self.current() == kind
+    }
+
+    /// Checks if the current token is contextual keyword with text `t`.
+    pub(crate) fn at_contextual_kw(&self, t: &str) -> bool {
+        self.0.at_kw(t)
+    }
+
+    /// Starts a new node in the syntax tree. All nodes and tokens
+    /// consumed between the `start` and the corresponding `Marker::complete`
+    /// belong to the same node.
+    pub(crate) fn start(&mut self) -> Marker {
+        Marker(self.0.start())
+    }
+
+    /// Advances the parser by one token.
+    pub(crate) fn bump(&mut self) {
+        self.0.bump();
+    }
+
+    /// Advances the parser by one token, remapping its kind.
+    /// This is useful to create contextual keywords from
+    /// identifiers. For example, the lexer creates an `union`
+    /// *identifier* token, but the parser remaps it to the
+    /// `union` keyword, and keyword is what ends up in the
+    /// final tree.
+    pub(crate) fn bump_remap(&mut self, kind: SyntaxKind) {
+        self.0.bump_remap(kind);
+    }
+
+    /// Emit error with the `message`
+    /// TODO: this should be much more fancy and support
+    /// structured errors with spans and notes, like rustc
+    /// does.
+    pub(crate) fn error<T: Into<String>>(&mut self, message: T) {
+        self.0.error(message.into())
+    }
+
+    /// Consume the next token if it is `kind`.
+    pub(crate) fn eat(&mut self, kind: SyntaxKind) -> bool {
+        if !self.at(kind) {
+            return false;
+        }
+        self.bump();
+        true
+    }
+
+    /// Consume the next token if it is `kind` or emit an error
+    /// otherwise.
+    pub(crate) fn expect(&mut self, kind: SyntaxKind) -> bool {
+        if self.eat(kind) {
+            return true;
+        }
+        self.error(format!("expected {:?}", kind));
+        false
+    }
+
+    /// Create an error node and consume the next token.
+    pub(crate) fn err_and_bump(&mut self, message: &str) {
+        let m = self.start();
+        self.error(message);
+        self.bump();
+        m.complete(self, ERROR);
+    }
+}
+
+/// See `Parser::start`.
+pub(crate) struct Marker(u32);
+
+impl Marker {
+    /// Finishes the syntax tree node and assigns `kind` to it.
+    pub(crate) fn complete(self, p: &mut Parser, kind: SyntaxKind) -> CompletedMarker {
+        let pos = self.0;
+        ::std::mem::forget(self);
+        p.0.complete(pos, kind);
+        CompletedMarker(pos)
+    }
+
+    /// Abandons the syntax tree node. All its children
+    /// are attached to its parent instead.
+    pub(crate) fn abandon(self, p: &mut Parser) {
+        let pos = self.0;
+        ::std::mem::forget(self);
+        p.0.abandon(pos);
+    }
+}
+
+impl Drop for Marker {
+    fn drop(&mut self) {
+        if !::std::thread::panicking() {
+            panic!("Marker must be either completed or abandoned");
+        }
+    }
+}
+
+pub(crate) struct CompletedMarker(u32);
+
+impl CompletedMarker {
+    /// This one is tricky :-)
+    /// This method allows to create a new node which starts
+    /// *before* the current one. That is, parser could start
+    /// node `A`, then complete it, and then after parsing the
+    /// whole `A`, decide that it should have started some node
+    /// `B` before starting `A`. `precede` allows to do exactly
+    /// that. See also docs about `forward_parent` in `Event::Start`.
+    pub(crate) fn precede(self, p: &mut Parser) -> Marker {
+        Marker(p.0.precede(self.0))
+    }
+}