From c99d9dec1c89a09fd4ba6f7f73a94bf5b29ee7f0 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Fri, 31 Jul 2026 09:23:21 +0100
Subject: Make Source a sealed interface

---
 src/main/java/org/shedlang/compiler/sources/NullSource.java    | 2 +-
 src/main/java/org/shedlang/compiler/sources/RuntimeSource.java | 2 +-
 src/main/java/org/shedlang/compiler/sources/Source.java        | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/main/java/org/shedlang/compiler/sources/NullSource.java b/src/main/java/org/shedlang/compiler/sources/NullSource.java
index 6a66aeea..fbac0ea0 100644
--- a/src/main/java/org/shedlang/compiler/sources/NullSource.java
+++ b/src/main/java/org/shedlang/compiler/sources/NullSource.java
@@ -1,6 +1,6 @@
 package org.shedlang.compiler.sources;
 
-public class NullSource implements Source {
+public final class NullSource implements Source {
     private NullSource() {
     }
 
diff --git a/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java b/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java
index 6bb708f9..749b84e3 100644
--- a/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java
+++ b/src/main/java/org/shedlang/compiler/sources/RuntimeSource.java
@@ -1,6 +1,6 @@
 package org.shedlang.compiler.sources;
 
-public class RuntimeSource implements Source {
+public final class RuntimeSource implements Source {
     private RuntimeSource() {
     }
 
diff --git a/src/main/java/org/shedlang/compiler/sources/Source.java b/src/main/java/org/shedlang/compiler/sources/Source.java
index edd9ad88..aeae447f 100644
--- a/src/main/java/org/shedlang/compiler/sources/Source.java
+++ b/src/main/java/org/shedlang/compiler/sources/Source.java
@@ -1,5 +1,5 @@
 package org.shedlang.compiler.sources;
 
-public interface Source {
+public sealed interface Source permits FileFragmentSource, NullSource, RuntimeSource {
     String describe();
 }
-- 
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