Use indexmap in specializationpriority

Author: pierwill

chalk-solve/src/coherence.rs

@@ -4,7 +4,6 @@ use crate::solve::Solver;
 use crate::RustIrDatabase;
 use chalk_ir::interner::Interner;
 use chalk_ir::{self, ImplId, TraitId};
-use std::collections::BTreeMap;
 use std::fmt;
 use std::sync::Arc;
 
@@ -42,13 +41,13 @@ impl<I: Interner> std::error::Error for CoherenceError<I> {}
 /// This basically encodes which impls specialize one another.
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct SpecializationPriorities<I: Interner> {
-    map: BTreeMap<ImplId<I>, SpecializationPriority>,
+    map: indexmap::IndexMap<ImplId<I>, SpecializationPriority>,
 }
 
 impl<I: Interner> SpecializationPriorities<I> {
     pub fn new() -> Self {
         Self {
-            map: BTreeMap::new(),
+            map: indexmap::IndexMap::new(),
         }
     }