depends 0.11.0

Ergonomic, performant, incremental computation between arbitrary types
Documentation 
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#[cfg(test)]
mod hash_one_ext;
#[cfg(feature = "hashbrown")]
pub mod hashbrown;

use std::{
    collections::{hash_map::DefaultHasher, HashSet},
    hash::{BuildHasher, Hasher},
};

use super::Identifiable;

/// The default [Visitor] type.
pub type HashSetVisitor = HashSet<usize>;

/// A collection passed in to a graph, tracking the identifiers of each nodes to
/// avoid traversing
pub trait Visitor {
    type Hasher: Hasher;

    /// Return true *iff* this node hasn't been visited yet.
    fn visit<N>(&mut self, node: &N) -> bool
    where
        N: Identifiable;

    /// Clear the internal collection, prompting this visitor to revisit all
    /// nodes on the next traversal.
    fn clear(&mut self);

    /// Touch the node. Useful for building graph visualisations.
    fn touch<N>(&mut self, _node: &N, _operation: Option<&'static str>)
    where
        N: Identifiable,
    {
    }

    /// For diagnostics, notify that a node has been recalculated.
    fn notify_recalculated<N>(&mut self, _node: &N)
    where
        N: Identifiable,
    {
    }

    /// Touch a dependency group type. Useful for building graph visualisations.
    fn touch_dependency_group(&mut self, _dep: &'static str) {}

    /// Undo a [touch](Self::touch). Useful for building graph visualisations.
    fn leave<N>(&mut self, _node: &N)
    where
        N: Identifiable,
    {
    }

    fn hasher(&self) -> Self::Hasher;
}

impl Visitor for HashSetVisitor {
    type Hasher = DefaultHasher;

    fn visit<N>(&mut self, node: &N) -> bool
    where
        N: Identifiable,
    {
        self.insert(node.id())
    }

    fn clear(&mut self) {
        self.clear()
    }

    fn hasher(&self) -> Self::Hasher {
        HashSetVisitor::hasher(self).build_hasher()
    }
}

/// A visitor which tracks the resolution state of each node it visits. This
/// is useful for debugging unexpected caching behaviour.
#[derive(Debug, Clone, Default)]
pub struct DiagnosticVisitor {
    pub visitor: HashSetVisitor,
    pub recalculated: HashSet<usize>,
}

impl Visitor for DiagnosticVisitor {
    type Hasher = DefaultHasher;

    fn visit<N>(&mut self, node: &N) -> bool
    where
        N: Identifiable,
    {
        self.visitor.visit(node)
    }

    fn clear(&mut self) {
        self.visitor.clear();
        self.recalculated.clear();
    }

    fn hasher(&self) -> Self::Hasher {
        <HashSetVisitor as Visitor>::hasher(&self.visitor)
    }

    fn notify_recalculated<N>(&mut self, node: &N)
    where
        N: Identifiable,
    {
        self.recalculated.insert(node.id());
    }
}

impl DiagnosticVisitor {
    #[allow(unused)]
    pub fn new() -> Self {
        Self::default()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::execution::visitor::hash_one_ext::hash_one;

    #[test]
    fn test_visitor_hasher() {
        let visitor = HashSetVisitor::default();
        let hasher_a = visitor.hasher();
        let hasher_b = visitor.hasher();
        assert_eq!(hash_one(hasher_a, 123), hash_one(hasher_b, 123));
    }
}