fix(studio-server): a drag back to its start claims nothing, and next steps name their files

Author: miguel-heygen

packages/studio-server/src/history/projectHistory.test.ts

@@ -334,6 +334,20 @@ describe("claim: a writer that records after writing", () => {
     expect(history.list()[0]).toMatchObject({ id: first!.id, files: [{ path: "index.html" }] });
   });
 
+  it("a coalescing claim whose writes net to nothing returns null and records nothing", async () => {
+    const { history, write } = await project({ "index.html": "A" });
+    write("index.html", "B");
+    expect(
+      await history.claim(you, "Dragged Title", ["index.html"], { coalesceKey: "drag" }),
+    ).not.toBeNull();
+    write("index.html", "A");
+    expect(
+      await history.claim(you, "Dragged Title", ["index.html"], { coalesceKey: "drag" }),
+    ).toBeNull();
+    await history.flush();
+    expect(history.list()).toEqual([]);
+  });
+
   it("a claim with another key, or its idle time, ends the coalescing claim", async () => {
     const { history, write } = await project({ "a.html": "A", "b.html": "B" });
     write("a.html", "A2");

packages/studio-server/src/history/projectHistory.ts

@@ -68,7 +68,8 @@ export interface ProjectHistory {
   /**
    * For a writer that records after writing (Studio): takes in every write so far and moves the not yet committed
    * outside changes to `paths` into one entry of `who`'s. Claims with the same coalesceKey merge until a claim with
-   * another key, `idleMs` (default quietMs) without one, or any operation. Null when nothing was claimed.
+   * another key, `idleMs` (default quietMs) without one, or any operation. Null when nothing was claimed, or
+   * when a coalescing claim's writes net to nothing (a drag back to where it started).
    */
   claim(
     who: HistoryWho,
@@ -313,12 +314,16 @@ class Engine {
     return taken;
   }
 
-  holdClaim(group: Group, key: string, idleMs = this.options.quietMs ?? 2000): { id: string } {
+  holdClaim(
+    group: Group,
+    key: string,
+    idleMs = this.options.quietMs ?? 2000,
+  ): { id: string } | null {
     clearTimeout(this.claimed?.timer);
     const timer = setTimeout(() => this.background(() => this.commitClaim()), idleMs);
     timer.unref?.();
     this.claimed = { group, key, timer };
-    return { id: group.id };
+    return group.changes.size ? { id: group.id } : null;
   }
 
   async commitClaim(): Promise<void> {

packages/studio-server/src/routes/history.test.ts

@@ -68,7 +68,7 @@ describe("history routes", () => {
     writeFileSync(join(projectDir, "index.html"), "B");
     await call(`/window/${windowId}/close`, {});
     expect(await (await call("")).json()).toMatchObject({
-      back: { id: windowId, label: "Moved Title" },
+      back: { id: windowId, label: "Moved Title", paths: ["index.html"] },
       forward: null,
     });
 

packages/studio-server/src/routes/history.ts

@@ -30,7 +30,9 @@ function idleOf(body: Record<string, unknown>): number | undefined {
 /** What Cmd+Z or Cmd+Shift+Z would revert next, so Studio can name it on its buttons. */
 function nextStep(entries: readonly HistoryEntry[], direction: "back" | "forward") {
   const target = stepTarget(entries, direction);
-  return target ? { id: target.id, label: target.label, endedAt: target.endedAt } : null;
+  if (!target) return null;
+  const paths = target.files.map((file) => file.path);
+  return { id: target.id, label: target.label, endedAt: target.endedAt, paths };
 }
 
 /** Runs `task` on the project's history; no history is a 404, an engine refusal ("no longer kept") a 409. */