From 5a6f661535dc06e718d4af907ef590e617497e47 Mon Sep 17 00:00:00 2001
From: Periapsises <94928308+Periapsises@users.noreply.github.com>
Date: Thu, 27 Aug 2026 18:15:56 -0400
Subject: [PATCH 1/3] Fix nested array types not matching their empty
 equivalent

---
 Crater/SemanticAnalysis/Types/ArrayType.cs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Crater/SemanticAnalysis/Types/ArrayType.cs b/Crater/SemanticAnalysis/Types/ArrayType.cs
index c0a6765..778b703 100644
--- a/Crater/SemanticAnalysis/Types/ArrayType.cs
+++ b/Crater/SemanticAnalysis/Types/ArrayType.cs
@@ -16,6 +16,9 @@ public override bool CanHold(Type other)
         if (other is EmptyArrayType)
             return true;
 
+        if (other is ArrayType otherArray)
+            return ElementType.CanHold(otherArray.ElementType);
+
         return IsSameType(other);
     }
 

From b684875ce7d5008a705cc085e4f8e0ed865aff70 Mon Sep 17 00:00:00 2001
From: Periapsises <94928308+Periapsises@users.noreply.github.com>
Date: Thu, 27 Aug 2026 18:30:25 -0400
Subject: [PATCH 2/3] Fix nested arrays being covariant

---
 Crater/SemanticAnalysis/Types/ArrayType.cs | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/Crater/SemanticAnalysis/Types/ArrayType.cs b/Crater/SemanticAnalysis/Types/ArrayType.cs
index 778b703..5318441 100644
--- a/Crater/SemanticAnalysis/Types/ArrayType.cs
+++ b/Crater/SemanticAnalysis/Types/ArrayType.cs
@@ -16,10 +16,16 @@ public override bool CanHold(Type other)
         if (other is EmptyArrayType)
             return true;
 
-        if (other is ArrayType otherArray)
-            return ElementType.CanHold(otherArray.ElementType);
+        if (other is not ArrayType otherArray)
+            return false;
 
-        return IsSameType(other);
+        if (otherArray.ElementType is EmptyArrayType)
+            return true;
+
+        if (ElementType is ArrayType selfElement && otherArray.ElementType is ArrayType otherElement)
+            return selfElement.CanHold(otherElement);
+
+        return ElementType.IsSameType(otherArray.ElementType);
     }
 
     public override bool IsSameType(Type other)

From 9b87ebc099ab7a72ae922ae1c9424a52862e9dee Mon Sep 17 00:00:00 2001
From: Periapsises <94928308+Periapsises@users.noreply.github.com>
Date: Thu, 27 Aug 2026 18:30:43 -0400
Subject: [PATCH 3/3] Add more tests for nested arrays

---
 Tests/ArrayTypeTests.cs | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/Tests/ArrayTypeTests.cs b/Tests/ArrayTypeTests.cs
index 0db783f..9dbe3c7 100644
--- a/Tests/ArrayTypeTests.cs
+++ b/Tests/ArrayTypeTests.cs
@@ -58,4 +58,41 @@ public void CanIndexRecursiveArrays()
         Assert.That(innerResult, Is.Not.Null);
         Assert.That(innerResult.IsSameType(new NullableType(TypeRegistry.NumberType)));
     }
+
+    [Test]
+    public void CanHoldNestedEmptyArray()
+    {
+        var numberArray = new ArrayType(TypeRegistry.NumberType, TypeRegistry.AnyType);
+        var nestedNumberArray = new ArrayType(numberArray, TypeRegistry.AnyType);
+        var nestedEmptyArray = new ArrayType(new EmptyArrayType(), TypeRegistry.AnyType);
+
+        Assert.That(nestedNumberArray.CanHold(nestedEmptyArray));
+    }
+
+    [Test]
+    public void CanHoldDeeplyNestedEmptyArray()
+    {
+        var numberArray = new ArrayType(TypeRegistry.NumberType, TypeRegistry.AnyType);
+        var nestedNumberArray = new ArrayType(numberArray, TypeRegistry.AnyType);
+        var deeplyNestedNumberArray = new ArrayType(nestedNumberArray, TypeRegistry.AnyType);
+
+        var emptyArray = new EmptyArrayType();
+        var nestedEmptyArray = new ArrayType(emptyArray, TypeRegistry.AnyType);
+        var deeplyNestedEmptyArray = new ArrayType(nestedEmptyArray, TypeRegistry.AnyType);
+
+        Assert.That(deeplyNestedNumberArray.CanHold(deeplyNestedEmptyArray));
+    }
+
+    [Test]
+    public void EmptyNestedArrayCannotHoldConcreteNestedArray()
+    {
+        var emptyArray = new EmptyArrayType();
+        var nestedEmptyArray = new ArrayType(emptyArray, TypeRegistry.AnyType);
+        var emptyNestedArray = new ArrayType(nestedEmptyArray, TypeRegistry.AnyType);
+
+        var numberArray = new ArrayType(TypeRegistry.NumberType, TypeRegistry.AnyType);
+        var nestedNumberArray = new ArrayType(numberArray, TypeRegistry.AnyType);
+
+        Assert.That(!emptyNestedArray.CanHold(nestedNumberArray));
+    }
 }