Remove scenario.lua when unpatching a save

Unpatching moves scenario.lua back to control.lua instead of copying it, so the save only keeps clusterio.json for the patch number. Patching such a save again copies control.lua back to scenario.lua.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/host/src/patch.ts

@@ -479,6 +479,16 @@ export async function patch(savePath: string, modules: SaveModule[]) {
 				);
 			}
 
+			// Unpatching put the original control.lua back in place of scenario.lua
+			const scenarioRequired = [...patchInfo.scenario.load, ...patchInfo.scenario.require].includes("scenario");
+			if (scenarioRequired && !zip.file(rootPath("scenario.lua"))) {
+				const control = await zip.readFile(rootPath("control.lua"));
+				if (control === null) {
+					throw new Error("Unable to patch save, missing control.lua file.");
+				}
+				files.set("scenario.lua", control);
+			}
+
 		// No info file present, try to detect if it's a known compatible scenario.
 		} else {
 			const controlFile = zip.file(rootPath("control.lua"));
@@ -527,8 +537,8 @@ export async function patch(savePath: string, modules: SaveModule[]) {
 /**
  * Remove the modules patched into a save
  *
- * Restores the original control.lua that patching kept as scenario.lua and
- * removes the module files.  The patch info is kept with no modules so that
+ * Moves the original control.lua that patching kept as scenario.lua back
+ * and removes the module files.  The patch info is kept with no modules so that
  * the patch number keeps counting if the save is patched again.
  *
  * @param savePath - Path to the Factorio save to unpatch.
@@ -557,9 +567,12 @@ export async function unpatch(savePath: string) {
 
 		const removed = moduleEntries(zip, patchInfo, root);
 		patchInfo.modules = [];
+		const scenario = await zip.readFile(rootPath("scenario.lua"));
+		if (scenario !== null) {
+			removed.add(rootPath("scenario.lua"));
+		}
 		// Scenarios made for Clusterio have no scenario.lua, keep loading them without modules
-		const control = await zip.readFile(rootPath("scenario.lua"))
-			?? Buffer.from(generateLoader(patchInfo), "utf8");
+		const control = scenario ?? Buffer.from(generateLoader(patchInfo), "utf8");
 		tempSavePath = await rewriteSave(zip, savePath, removed, new Map([
 			[rootPath("control.lua"), control],
 			[rootPath("clusterio.json"), Buffer.from(JSON.stringify(patchInfo, null, "\t"), "utf8")],

test/host/patch.js

@@ -309,7 +309,7 @@ describe("host/patch", function() {
 			const files = await readSave();
 			assert.deepEqual(
 				[...files.keys()].sort(),
-				["world/clusterio.json", "world/control.lua", "world/level.dat0", "world/scenario.lua"],
+				["world/clusterio.json", "world/control.lua", "world/level.dat0"],
 			);
 			assert.equal(files.get("world/control.lua"), freeplayControl);
 			const patchInfo = JSON.parse(files.get("world/clusterio.json"));
@@ -337,6 +337,8 @@ describe("host/patch", function() {
 			const files = await readSave();
 			assert.equal(JSON.parse(files.get("world/clusterio.json")).patch_number, 2);
 			assert(files.has("world/modules/test/test.lua"));
+			assert.equal(files.get("world/scenario.lua"), freeplayControl);
+			assert.match(files.get("world/control.lua"), /^-- Auto generated scenario module loader/);
 		});
 		it("should keep the loader of scenarios made for Clusterio", async function() {
 			const scenario = new lib.ModuleInfo("custom", "1.0.0", [], ["custom"]);