Support looping storage references

runtime/interpreter/value.go

@@ -19844,6 +19844,7 @@ var _ TypeIndexableValue = &StorageReferenceValue{}
 var _ MemberAccessibleValue = &StorageReferenceValue{}
 var _ AuthorizedValue = &StorageReferenceValue{}
 var _ ReferenceValue = &StorageReferenceValue{}
+var _ IterableValue = &StorageReferenceValue{}
 
 func NewUnmeteredStorageReferenceValue(
 	authorization Authorization,
@@ -20196,6 +20197,37 @@ func (*StorageReferenceValue) DeepRemove(_ *Interpreter) {
 
 func (*StorageReferenceValue) isReference() {}
 
+func (v *StorageReferenceValue) Iterator(interpreter *Interpreter, locationRange LocationRange) ValueIterator {
+	referencedValue := v.mustReferencedValue(interpreter, locationRange)
+	return referenceValueIterator(interpreter, referencedValue, v.BorrowedType, locationRange)
+}
+
+func referenceValueIterator(
+	interpreter *Interpreter,
+	referencedValue Value,
+	borrowedType sema.Type,
+	locationRange LocationRange,
+) ValueIterator {
+	referencedIterable, ok := referencedValue.(IterableValue)
+	if !ok {
+		panic(errors.NewUnreachableError())
+	}
+
+	referencedValueIterator := referencedIterable.Iterator(interpreter, locationRange)
+
+	referencedType, ok := borrowedType.(sema.ValueIndexableType)
+	if !ok {
+		panic(errors.NewUnreachableError())
+	}
+
+	elementType := referencedType.ElementType(false)
+
+	return ReferenceValueIterator{
+		iterator:    referencedValueIterator,
+		elementType: elementType,
+	}
+}
+
 // EphemeralReferenceValue
 
 type EphemeralReferenceValue struct {
@@ -20544,21 +20576,11 @@ func (*EphemeralReferenceValue) isReference() {}
 
 func (v *EphemeralReferenceValue) Iterator(interpreter *Interpreter, locationRange LocationRange) ValueIterator {
 	referencedValue := v.MustReferencedValue(interpreter, locationRange)
-	referenceValueIterator := referencedValue.(IterableValue).Iterator(interpreter, locationRange)
-
-	referencedType, ok := v.BorrowedType.(sema.ValueIndexableType)
-	if !ok {
-		panic(errors.NewUnreachableError())
-	}
-
-	elementType := referencedType.ElementType(false)
-
-	return ReferenceValueIterator{
-		iterator:    referenceValueIterator,
-		elementType: elementType,
-	}
+	return referenceValueIterator(interpreter, referencedValue, v.BorrowedType, locationRange)
 }
 
+// ReferenceValueIterator
+
 type ReferenceValueIterator struct {
 	iterator    ValueIterator
 	elementType sema.Type
@@ -20573,6 +20595,7 @@ func (i ReferenceValueIterator) Next(interpreter *Interpreter) Value {
 		return nil
 	}
 
+	// For non-primitive values, return a reference.
 	if i.elementType.ContainFieldsOrElements() {
 		return NewEphemeralReferenceValue(interpreter, UnauthorizedAccess, element, i.elementType)
 	}

runtime/tests/interpreter/for_test.go

@@ -19,6 +19,7 @@
 package interpreter_test
 
 import (
+	"github.com/onflow/cadence/runtime/sema"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -295,7 +296,7 @@ func TestInterpretForStatementCapturing(t *testing.T) {
 	)
 }
 
-func TestInterpretReferencesInForLoop(t *testing.T) {
+func TestInterpretEphemeralReferencesInForLoop(t *testing.T) {
 
 	t.Parallel()
 
@@ -386,3 +387,102 @@ func TestInterpretReferencesInForLoop(t *testing.T) {
 		require.ErrorAs(t, err, &interpreter.InvalidatedResourceReferenceError{})
 	})
 }
+
+func TestInterpretStorageReferencesInForLoop(t *testing.T) {
+
+	t.Parallel()
+
+	t.Run("Primitive array", func(t *testing.T) {
+		t.Parallel()
+
+		address := interpreter.NewUnmeteredAddressValueFromBytes([]byte{42})
+
+		inter, _ := testAccount(t, address, true, nil, `
+            fun test() {
+                var array = ["Hello", "World", "Foo", "Bar"]
+                account.storage.save(array, to: /storage/array)
+
+                let arrayRef = account.storage.borrow<&[String]>(from: /storage/array)!
+
+                for element in arrayRef {
+                    let e: String = element    // Must be the concrete string
+                }
+            }`, sema.Config{})
+
+		_, err := inter.Invoke("test")
+		require.NoError(t, err)
+	})
+
+	t.Run("Struct array", func(t *testing.T) {
+		t.Parallel()
+
+		address := interpreter.NewUnmeteredAddressValueFromBytes([]byte{42})
+
+		inter, _ := testAccount(t, address, true, nil, `
+            struct Foo{}
+
+            fun test() {
+                var array = [Foo(), Foo()]
+                account.storage.save(array, to: /storage/array)
+
+                let arrayRef = account.storage.borrow<&[Foo]>(from: /storage/array)!
+
+                for element in arrayRef {
+                    let e: &Foo = element    // Must be a reference
+                }
+            }`, sema.Config{})
+
+		_, err := inter.Invoke("test")
+		require.NoError(t, err)
+	})
+
+	t.Run("Resource array", func(t *testing.T) {
+		t.Parallel()
+
+		address := interpreter.NewUnmeteredAddressValueFromBytes([]byte{42})
+
+		inter, _ := testAccount(t, address, true, nil, `
+            resource Foo{}
+
+            fun test() {
+                var array <- [ <- create Foo(), <- create Foo()]
+                account.storage.save(<- array, to: /storage/array)
+
+                let arrayRef = account.storage.borrow<&[Foo]>(from: /storage/array)!
+
+                for element in arrayRef {
+                    let e: &Foo = element    // Must be a reference
+                }
+            }`, sema.Config{})
+
+		_, err := inter.Invoke("test")
+		require.NoError(t, err)
+	})
+
+	t.Run("Moved resource array", func(t *testing.T) {
+		t.Parallel()
+
+		address := interpreter.NewUnmeteredAddressValueFromBytes([]byte{42})
+
+		inter, _ := testAccount(t, address, true, nil, `
+            resource Foo{}
+
+            fun test() {
+                var array <- [ <- create Foo(), <- create Foo()]
+                account.storage.save(<- array, to: /storage/array)
+
+                let arrayRef = account.storage.borrow<&[Foo]>(from: /storage/array)!
+
+                let movedArray <- account.storage.load<@[Foo]>(from: /storage/array)!
+
+                for element in arrayRef {
+                    let e: &Foo = element    // Must be a reference
+                }
+
+                destroy movedArray
+            }`, sema.Config{})
+
+		_, err := inter.Invoke("test")
+		require.ErrorAs(t, err, &interpreter.DereferenceError{})
+	})
+}