Support (no-op) type substitution for struct types

2 files changed, 16 insertions, 3 deletions

diff --git a/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java b/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java
index a6719d17..5d2b7077 100644
--- a/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java
+++ b/src/main/java/org/shedlang/compiler/types/TypeSubstitution.java
@@ -33,9 +33,8 @@ public class TypeSubstitution {
 
             case StringType stringType -> type;
 
-            case StructType structType -> {
-                throw new UnsupportedOperationException("TODO");
-            }
+            case StructType structType ->
+                type;
 
             case SumType sumType -> {
                 throw new UnsupportedOperationException("TODO");
diff --git a/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java b/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java
index e9b04a95..d6713ee0 100644
--- a/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java
+++ b/src/test/java/org/shedlang/compiler/types/TypeSubstitutionTests.java
@@ -154,6 +154,20 @@ public class TypeSubstitutionTests {
     }
 
     @Test
+    public void substitutingStructDoesNothing() {
+        var typeSubstitutionMap = TypeSubstitutionMap.of(
+            Map.entry(TypeParam.forStructType(STRUCT_TYPE, "T"), Types.INT)
+        );
+
+        var result = TypeSubstitution.substitute(
+            Types.struct(NamespaceName.of("A"), "B"),
+            typeSubstitutionMap
+        );
+
+        assertThat(result, equalTo(Types.struct(NamespaceName.of("A"), "B")));
+    }
+
+    @Test
     public void substitutingTopDoesNothing() {
         var typeSubstitutionMap = TypeSubstitutionMap.of(
             Map.entry(TypeParam.forStructType(STRUCT_TYPE, "T"), Types.INT)