1 files changed, 199 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/parsing/parser_impl.rs b/crates/ra_syntax/src/parsing/parser_impl.rs
new file mode 100644
index 000000000..c639d83e8
--- /dev/null
+++ b/crates/ra_syntax/src/parsing/parser_impl.rs
@@ -0,0 +1,199 @@
+mod event;
+mod input;
+
+use std::cell::Cell;
+
+use crate::{
+    SmolStr,
+    syntax_node::syntax_error::{ParseError, SyntaxError},
+    parsing::{
+    lexer::Token,
+    parser_api::Parser,
+    parser_impl::{
+        event::{Event, EventProcessor},
+        input::{InputPosition, ParserInput},
+    },
+}};
+
+use crate::SyntaxKind::{self, EOF, TOMBSTONE};
+
+pub(crate) trait Sink {
+    type Tree;
+
+    /// Adds new leaf to the current branch.
+    fn leaf(&mut self, kind: SyntaxKind, text: SmolStr);
+
+    /// Start new branch and make it current.
+    fn start_branch(&mut self, kind: SyntaxKind);
+
+    /// Finish current branch and restore previous
+    /// branch as current.
+    fn finish_branch(&mut self);
+
+    fn error(&mut self, error: SyntaxError);
+
+    /// Complete tree building. Make sure that
+    /// `start_branch` and `finish_branch` calls
+    /// are paired!
+    fn finish(self) -> Self::Tree;
+}
+
+/// Parse a sequence of tokens into the representative node tree
+pub(crate) fn parse_with<S: Sink>(
+    sink: S,
+    text: &str,
+    tokens: &[Token],
+    parser: fn(&mut Parser),
+) -> S::Tree {
+    let mut events = {
+        let input = input::ParserInput::new(text, tokens);
+        let parser_impl = ParserImpl::new(&input);
+        let mut parser_api = Parser(parser_impl);
+        parser(&mut parser_api);
+        parser_api.0.into_events()
+    };
+    EventProcessor::new(sink, text, tokens, &mut events).process().finish()
+}
+
+/// Implementation details of `Parser`, extracted
+/// to a separate struct in order not to pollute
+/// the public API of the `Parser`.
+pub(crate) struct ParserImpl<'t> {
+    parser_input: &'t ParserInput<'t>,
+    pos: InputPosition,
+    events: Vec<Event>,
+    steps: Cell<u32>,
+}
+
+impl<'t> ParserImpl<'t> {
+    fn new(inp: &'t ParserInput<'t>) -> ParserImpl<'t> {
+        ParserImpl {
+            parser_input: inp,
+            pos: InputPosition::new(),
+            events: Vec::new(),
+            steps: Cell::new(0),
+        }
+    }
+
+    fn into_events(self) -> Vec<Event> {
+        assert_eq!(self.nth(0), EOF);
+        self.events
+    }
+
+    pub(super) fn current2(&self) -> Option<(SyntaxKind, SyntaxKind)> {
+        let c1 = self.parser_input.kind(self.pos);
+        let c2 = self.parser_input.kind(self.pos + 1);
+        if self.parser_input.token_start_at(self.pos + 1)
+            == self.parser_input.token_start_at(self.pos) + self.parser_input.token_len(self.pos)
+        {
+            Some((c1, c2))
+        } else {
+            None
+        }
+    }
+
+    pub(super) fn current3(&self) -> Option<(SyntaxKind, SyntaxKind, SyntaxKind)> {
+        let c1 = self.parser_input.kind(self.pos);
+        let c2 = self.parser_input.kind(self.pos + 1);
+        let c3 = self.parser_input.kind(self.pos + 2);
+        if self.parser_input.token_start_at(self.pos + 1)
+            == self.parser_input.token_start_at(self.pos) + self.parser_input.token_len(self.pos)
+            && self.parser_input.token_start_at(self.pos + 2)
+                == self.parser_input.token_start_at(self.pos + 1)
+                    + self.parser_input.token_len(self.pos + 1)
+        {
+            Some((c1, c2, c3))
+        } else {
+            None
+        }
+    }
+
+    /// Get the syntax kind of the nth token.
+    pub(super) fn nth(&self, n: u32) -> SyntaxKind {
+        let steps = self.steps.get();
+        assert!(steps <= 10_000_000, "the parser seems stuck");
+        self.steps.set(steps + 1);
+
+        self.parser_input.kind(self.pos + n)
+    }
+
+    pub(super) fn at_kw(&self, t: &str) -> bool {
+        self.parser_input.token_text(self.pos) == t
+    }
+
+    /// Start parsing right behind the last event.
+    pub(super) fn start(&mut self) -> u32 {
+        let pos = self.events.len() as u32;
+        self.push_event(Event::tombstone());
+        pos
+    }
+
+    /// Advances the parser by one token unconditionally.
+    pub(super) fn bump(&mut self) {
+        let kind = self.nth(0);
+        if kind == EOF {
+            return;
+        }
+        self.do_bump(kind, 1);
+    }
+
+    pub(super) fn bump_remap(&mut self, kind: SyntaxKind) {
+        if self.nth(0) == EOF {
+            // TODO: panic!?
+            return;
+        }
+        self.do_bump(kind, 1);
+    }
+
+    pub(super) fn bump_compound(&mut self, kind: SyntaxKind, n: u8) {
+        self.do_bump(kind, n);
+    }
+
+    fn do_bump(&mut self, kind: SyntaxKind, n_raw_tokens: u8) {
+        self.pos += u32::from(n_raw_tokens);
+        self.push_event(Event::Token { kind, n_raw_tokens });
+    }
+
+    /// Append one Error event to the back of events.
+    pub(super) fn error(&mut self, msg: String) {
+        self.push_event(Event::Error { msg: ParseError(msg) })
+    }
+
+    /// Complete an event with appending a `Finish` event.
+    pub(super) fn complete(&mut self, pos: u32, kind: SyntaxKind) {
+        match self.events[pos as usize] {
+            Event::Start { kind: ref mut slot, .. } => {
+                *slot = kind;
+            }
+            _ => unreachable!(),
+        }
+        self.push_event(Event::Finish);
+    }
+
+    /// Ignore the dummy `Start` event.
+    pub(super) fn abandon(&mut self, pos: u32) {
+        let idx = pos as usize;
+        if idx == self.events.len() - 1 {
+            match self.events.pop() {
+                Some(Event::Start { kind: TOMBSTONE, forward_parent: None }) => (),
+                _ => unreachable!(),
+            }
+        }
+    }
+
+    /// Save the relative distance of a completed event to its forward_parent.
+    pub(super) fn precede(&mut self, pos: u32) -> u32 {
+        let new_pos = self.start();
+        match self.events[pos as usize] {
+            Event::Start { ref mut forward_parent, .. } => {
+                *forward_parent = Some(new_pos - pos);
+            }
+            _ => unreachable!(),
+        }
+        new_pos
+    }
+
+    fn push_event(&mut self, event: Event) {
+        self.events.push(event)
+    }
+}