Support newtypes and unit tag union hash deriving

crates/compiler/derive/src/hash.rs

@@ -27,13 +27,7 @@ use crate::{synth_var, util::Env, DerivedBody};
 pub(crate) fn derive_hash(env: &mut Env<'_>, key: FlatHashKey, def_symbol: Symbol) -> DerivedBody {
     let (body_type, body) = match key {
         FlatHashKey::Record(fields) => hash_record(env, def_symbol, fields),
-        FlatHashKey::TagUnion(tags) => {
+        FlatHashKey::TagUnion(tags) => hash_tag_union(env, def_symbol, tags),
-            if tags.len() > 1 {
-                hash_tag_union(env, def_symbol, tags)
-            } else {
-                todo!()
-            }
-        }
     };
 
     let specialization_lambda_sets =

crates/compiler/test_derive/src/hash.rs

@@ -201,6 +201,47 @@ fn two_field_record() {
     })
 }
 
+#[test]
+fn tag_one_label_no_payloads() {
+    derive_test(Hash, v!([A]), |golden| {
+        assert_snapshot!(golden, @r###"
+        # derived for [A]
+        # a, [A] -[[hash_[A 0](0)]]-> a | a has Hasher
+        # a, [A] -[[hash_[A 0](0)]]-> a | a has Hasher
+        # Specialization lambda sets:
+        #   @<1>: [[hash_[A 0](0)]]
+        #Derived.hash_[A 0] =
+          \#Derived.hasher, #Derived.union ->
+            #Derived.discrHasher =
+              Hash.hash #Derived.hasher (@tag_discriminant #Derived.union)
+            when #Derived.union is
+              A -> #Derived.discrHasher
+        "###
+        )
+    })
+}
+
+#[test]
+fn tag_one_label_newtype() {
+    derive_test(Hash, v!([A v!(U8) v!(STR)]), |golden| {
+        assert_snapshot!(golden, @r###"
+        # derived for [A U8 Str]
+        # a, [A a1 a2] -[[hash_[A 2](0)]]-> a | a has Hasher, a1 has Hash, a2 has Hash
+        # a, [A a1 a2] -[[hash_[A 2](0)]]-> a | a has Hasher, a1 has Hash, a2 has Hash
+        # Specialization lambda sets:
+        #   @<1>: [[hash_[A 2](0)]]
+        #Derived.hash_[A 2] =
+          \#Derived.hasher, #Derived.union ->
+            #Derived.discrHasher =
+              Hash.hash #Derived.hasher (@tag_discriminant #Derived.union)
+            when #Derived.union is
+              A #Derived.4 #Derived.5 ->
+                Hash.hash (Hash.hash #Derived.discrHasher #Derived.4) #Derived.5
+        "###
+        )
+    })
+}
+
 #[test]
 fn tag_two_labels() {
     derive_test(Hash, v!([A v!(U8) v!(STR) v!(U16), B v!(STR)]), |golden| {