tor_netdoc/parse2/
structural.rs

1//! Structural keyword recognition helpers
2
3use super::*;
4
5/// Predicate for testing whether a keyword is a structural one that we should stop at
6///
7/// This helper type allows us to compose predicates in curried form with `|`.
8#[derive(Debug, Copy, Clone, derive_more::Deref)]
9#[allow(clippy::exhaustive_structs)]
10pub struct StopAt<P: StopPredicate>(pub P);
11
12/// Raw predicate, usually a closure, that can appear within `StopAt`.
13///
14/// Implemented for suitable closures, and also for booleans.
15pub trait StopPredicate: Copy {
16    /// Is this keyword a structural one meaning we should stop parsing here?
17    ///
18    /// Precisely what the semantics are depends on the context.
19    /// Typically, matched keywords will cause processing to continue
20    /// in a subsequent document section, or in an outer (containing) document.
21    fn stop_at(&self, kw: KeywordRef<'_>) -> bool;
22}
23impl<F: Copy + Fn(KeywordRef<'_>) -> bool> StopPredicate for F {
24    fn stop_at(&self, kw: KeywordRef<'_>) -> bool {
25        self(kw)
26    }
27}
28impl StopPredicate for bool {
29    fn stop_at(&self, _kw: KeywordRef<'_>) -> bool {
30        *self
31    }
32}
33
34/// "Type alias" for `StopAt<impl Fn(KeywordRef<'_>) -> Option<Stop>>`
35///
36/// This has to be a macro because the `impl` is a different type at each call site;
37/// even TAIT wouldn't help with thaat.
38#[macro_export]
39macro_rules! stop_at { {} => {
40    $crate::parse2::internal_prelude::StopAt<
41        impl $crate::parse2::internal_prelude::StopPredicate
42    >
43} }
44
45impl StopAt<bool> {
46    /// Returns predicate flagging precisely the intro keywords for a parseable document
47    pub fn doc_intro<D: NetdocParseable>() -> stop_at!() {
48        StopAt(D::is_intro_item_keyword)
49    }
50}
51
52/// Helper type: return value from `StopAt | StopAt`
53#[derive(Debug, Copy, Clone)]
54pub struct BitOrOutput<A, B>(A, B);
55
56impl<A: StopPredicate, B: StopPredicate> std::ops::BitOr<StopAt<B>> for StopAt<A> {
57    type Output = StopAt<BitOrOutput<A, B>>;
58    fn bitor(self, rhs: StopAt<B>) -> Self::Output {
59        StopAt(BitOrOutput(self.0, rhs.0))
60    }
61}
62
63impl<A: StopPredicate, B: StopPredicate> StopPredicate for BitOrOutput<A, B> {
64    fn stop_at(&self, kw: KeywordRef<'_>) -> bool {
65        self.0.stop_at(kw) || self.1.stop_at(kw)
66    }
67}
tor_netdoc/parse2/structural.rs

tor_netdoc/parse2/
structural.rs
