Start using multimap correctly for path tracking in RojoTree

src/multimap.rs

@@ -0,0 +1,69 @@
+use std::{
+    borrow::Borrow,
+    collections::HashMap,
+    fmt::{self, Debug},
+    hash::Hash,
+};
+
+/// A map whose value contains a set of multiple values.
+#[derive(Clone)]
+pub struct MultiMap<K, V> {
+    inner: HashMap<K, Vec<V>>,
+}
+
+#[allow(dead_code)] // This is a core library-ish struct, unused stuff is ok
+impl<K: Hash + Eq, V: Eq> MultiMap<K, V> {
+    pub fn new() -> Self {
+        MultiMap {
+            inner: HashMap::new(),
+        }
+    }
+
+    pub fn get<Q: Borrow<K>>(&mut self, k: Q) -> &[V] {
+        self.inner.get(k.borrow()).map(Vec::as_slice).unwrap_or(&[])
+    }
+
+    pub fn insert(&mut self, k: K, v: V) {
+        let bucket = self.inner.entry(k).or_default();
+
+        for value in &*bucket {
+            if &*value == &v {
+                return;
+            }
+        }
+
+        bucket.push(v);
+    }
+
+    pub fn remove<Q: Borrow<K>, U: Borrow<V>>(&mut self, k: Q, v: U) -> Option<V> {
+        let b = v.borrow();
+
+        if let Some(bucket) = self.inner.get_mut(k.borrow()) {
+            let mut removed_value = None;
+
+            if let Some(index) = bucket.iter().position(|value| value == b) {
+                removed_value = Some(bucket.swap_remove(index));
+            }
+
+            if bucket.len() == 0 {
+                self.inner.remove(k.borrow());
+            }
+
+            removed_value
+        } else {
+            None
+        }
+    }
+}
+
+impl<K: Debug + Hash + Eq, V: Debug + Eq> Debug for MultiMap<K, V> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        self.inner.fmt(formatter)
+    }
+}
+
+impl<K: Hash + Eq, V: Eq> PartialEq for MultiMap<K, V> {
+    fn eq(&self, other: &Self) -> bool {
+        self.inner == other.inner
+    }
+}