Hide subs behind Env deref

Cargo.lock

@@ -4022,6 +4022,7 @@ name = "roc_unify"
 version = "0.0.1"
 dependencies = [
  "bitflags",
+ "roc_checkmate",
  "roc_collections",
  "roc_debug_flags",
  "roc_error_macros",

crates/compiler/unify/Cargo.toml

@@ -27,3 +27,6 @@ path = "../debug_flags"
 
 [dependencies.roc_tracing]
 path = "../../tracing"
+
+[dependencies.roc_checkmate]
+path = "../checkmate"

crates/compiler/unify/src/env.rs

@@ -0,0 +1,78 @@
+use roc_collections::VecSet;
+use roc_types::subs::{Subs, Variable};
+
+pub struct Env<'a> {
+    subs: &'a mut Subs,
+    seen_recursion: VecSet<(Variable, Variable)>,
+    fixed_variables: VecSet<Variable>,
+}
+
+impl std::ops::Deref for Env<'_> {
+    type Target = Subs;
+
+    fn deref(&self) -> &Self::Target {
+        self.subs
+    }
+}
+
+impl std::ops::DerefMut for Env<'_> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.subs
+    }
+}
+
+impl<'a> Env<'a> {
+    pub fn new(subs: &'a mut Subs) -> Self {
+        Self {
+            subs,
+            seen_recursion: Default::default(),
+            fixed_variables: Default::default(),
+        }
+    }
+
+    pub fn add_recursion_pair(&mut self, var1: Variable, var2: Variable) {
+        let pair = (
+            self.subs.get_root_key_without_compacting(var1),
+            self.subs.get_root_key_without_compacting(var2),
+        );
+
+        let already_seen = self.seen_recursion.insert(pair);
+        debug_assert!(!already_seen);
+    }
+
+    pub fn remove_recursion_pair(&mut self, var1: Variable, var2: Variable) {
+        #[cfg(debug_assertions)]
+        let size_before = self.seen_recursion.len();
+
+        self.seen_recursion.retain(|(v1, v2)| {
+            let is_recursion_pair = self.subs.equivalent_without_compacting(*v1, var1)
+                && self.subs.equivalent_without_compacting(*v2, var2);
+            !is_recursion_pair
+        });
+
+        #[cfg(debug_assertions)]
+        let size_after = self.seen_recursion.len();
+
+        #[cfg(debug_assertions)]
+        debug_assert!(size_after < size_before, "nothing was removed");
+    }
+
+    pub fn seen_recursion_pair(&self, var1: Variable, var2: Variable) -> bool {
+        let (var1, var2) = (
+            self.subs.get_root_key_without_compacting(var1),
+            self.subs.get_root_key_without_compacting(var2),
+        );
+
+        self.seen_recursion.contains(&(var1, var2))
+    }
+
+    pub fn was_fixed(&self, var: Variable) -> bool {
+        self.fixed_variables
+            .iter()
+            .any(|fixed_var| self.subs.equivalent_without_compacting(*fixed_var, var))
+    }
+
+    pub fn extend_fixed_variables(&mut self, vars: impl IntoIterator<Item = Variable>) {
+        self.fixed_variables.extend(vars);
+    }
+}

crates/compiler/unify/src/lib.rs

@@ -4,5 +4,6 @@
 // See github.com/roc-lang/roc/issues/800 for discussion of the large_enum_variant check.
 #![allow(clippy::large_enum_variant)]
 
+mod env;
 mod fix;
 pub mod unify;