feat(web): the Merge button remembers the method last run on a repository

apps/web/src/components/pull-requests/PullRequestDetailPanel.browser.tsx

@@ -261,6 +261,9 @@ describe("PullRequestDetailPanel", () => {
     // The merge dialog remembers this per computer, so one test's tick would
     // otherwise be the next one's default.
     window.localStorage.removeItem(`threadlines:pull-requests:delete-branch:v1:${ENVIRONMENT_ID}`);
+    window.localStorage.removeItem(
+      "threadlines:pull-requests:merge-method:v1:github:threadlines/threadlines",
+    );
   });
 
   it("renders the header, the checks that need attention, and the conversation", async () => {
@@ -693,4 +696,34 @@ describe("PullRequestDetailPanel", () => {
 
     await rendered.cleanup();
   });
+
+  it("wears the method last run on the repository and runs it next time", async () => {
+    const viewer = { canWrite: true, canReview: false, canManage: true };
+    const first = await renderPanel({ detail: { viewer } });
+
+    // The repository lists squash first, so that is the button's own until a
+    // choice is made. The menu spells the methods out in full.
+    await expect.element(page.getByTestId("pull-request-merge")).toHaveTextContent("Squash");
+    await userEvent.click(page.getByRole("button", { name: "Choose a merge method" }));
+    await userEvent.click(page.getByRole("menuitem", { name: "Create a merge commit" }));
+    const dialog = page.getByRole("alertdialog");
+    await expect.element(dialog.getByText("Create a merge commit.")).toBeVisible();
+    await userEvent.click(dialog.getByRole("button", { name: "Merge" }));
+    await vi.waitFor(() => {
+      expect(first.runAction).toHaveBeenCalledWith({
+        ...REFERENCE,
+        action: "merge",
+        mergeMethod: "merge",
+      });
+    });
+    await first.cleanup();
+
+    const second = await renderPanel({ detail: { viewer } });
+    await expect.element(page.getByTestId("pull-request-merge")).toHaveTextContent("Merge");
+    await userEvent.click(page.getByTestId("pull-request-merge"));
+    await expect
+      .element(page.getByRole("alertdialog").getByText("Create a merge commit."))
+      .toBeVisible();
+    await second.cleanup();
+  });
 });

apps/web/src/components/pull-requests/PullRequestDetailPanel.tsx

@@ -12,6 +12,7 @@ import type {
   ScopedThreadRef,
   SourceControlProviderKind,
 } from "@threadlines/contracts";
+import { PullRequestMergeMethod as PullRequestMergeMethodSchema } from "@threadlines/contracts";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { useNavigate } from "@tanstack/react-router";
 import * as Schema from "effect/Schema";
@@ -94,6 +95,7 @@ import {
 } from "./pullRequestPresentation";
 import {
   PULL_REQUEST_MERGE_METHOD_LABELS,
+  PULL_REQUEST_MERGE_METHOD_WORDS,
   appendHandoffToDraft,
   buildReviewCommentHandoff,
   formatPullRequestBaseFreshness,
@@ -1061,6 +1063,11 @@ type PullRequestConfirmation =
 /** Remembered per computer: whoever deletes merged branches always does. */
 const DELETE_BRANCH_STORAGE_PREFIX = "threadlines:pull-requests:delete-branch:v1";
 
+/** Remembered per repository: the merge method last run on it becomes the
+ *  Merge button's own, as the host's site does. */
+const MERGE_METHOD_STORAGE_PREFIX = "threadlines:pull-requests:merge-method:v1";
+const REMEMBERED_MERGE_METHOD_SCHEMA = Schema.NullOr(PullRequestMergeMethodSchema);
+
 /** The three pieces the header hangs in three different places. */
 interface PullRequestActionsView {
   /** The buttons, for the right of the header's first row. */
@@ -1104,6 +1111,11 @@ function usePullRequestActions({
     false,
     Schema.Boolean,
   );
+  const [rememberedMergeMethod, setRememberedMergeMethod] = useLocalStorage(
+    `${MERGE_METHOD_STORAGE_PREFIX}:${detail.provider}:${detail.repository}`,
+    null,
+    REMEMBERED_MERGE_METHOD_SCHEMA,
+  );
 
   const isRunning = mutation.isPending;
   const runningAction = isRunning ? (mutation.variables?.action ?? null) : null;
@@ -1144,7 +1156,7 @@ function usePullRequestActions({
   const updateMethods = detail.capabilities.updateMethods;
   const mergeBlock = resolvePullRequestMergeBlock(detail);
   const mergeDisabled = isRunning || mergeBlock !== null;
-  const defaultMergeMethod = resolveDefaultMergeMethod(detail.mergeMethods);
+  const defaultMergeMethod = resolveDefaultMergeMethod(detail.mergeMethods, rememberedMergeMethod);
   const canUpdateBranch = canWrite && isOpen && allows("update-branch");
   const isBehind = detail.baseComparison === "behind";
 
@@ -1180,7 +1192,9 @@ function usePullRequestActions({
         data-testid="pull-request-merge"
         onClick={() => setConfirming({ action: "merge", mergeMethod: defaultMergeMethod })}
       >
-        {runningAction === "merge" ? RUNNING_ACTION_WORDS.merge : "Merge"}
+        {runningAction === "merge"
+          ? RUNNING_ACTION_WORDS.merge
+          : PULL_REQUEST_MERGE_METHOD_WORDS[defaultMergeMethod]}
       </Button>
       {detail.mergeMethods.length > 1 ? (
         <Menu>
@@ -1329,7 +1343,7 @@ function usePullRequestActions({
                     setConfirming({ action: "merge", mergeMethod: defaultMergeMethod })
                   }
                 >
-                  Merge
+                  {PULL_REQUEST_MERGE_METHOD_LABELS[defaultMergeMethod]}
                 </MenuItem>
               ) : null}
               {handoffs ? (
@@ -1456,6 +1470,7 @@ function usePullRequestActions({
             onClick={() => {
               setConfirming(null);
               if (confirming.action === "merge") {
+                setRememberedMergeMethod(confirming.mergeMethod);
                 run("merge", {
                   mergeMethod: confirming.mergeMethod,
                   ...(deleteBranch ? { deleteBranch: true } : {}),

apps/web/src/components/pull-requests/pullRequests.logic.test.ts

@@ -37,6 +37,7 @@ import {
   pullRequestFiltersFromSearch,
   pullRequestFiltersToSearch,
   pullRequestLabelColor,
+  resolveDefaultMergeMethod,
   resolveNeedsYouReason,
   resolvePullRequestMergeBlock,
   resolvePullRequestReviewPosition,
@@ -1221,3 +1222,15 @@ describe("applyPendingPullRequestReactions", () => {
     ).toEqual([{ content: "thumbs-up", count: 3, viewerReacted: true }]);
   });
 });
+
+describe("resolveDefaultMergeMethod", () => {
+  it("runs the method last used on the repository while it is still allowed", () => {
+    expect(resolveDefaultMergeMethod(["merge", "squash", "rebase"], "squash")).toBe("squash");
+  });
+
+  it("falls back to the repository's first method when nothing is remembered or it is off", () => {
+    expect(resolveDefaultMergeMethod(["squash", "rebase"], "merge")).toBe("squash");
+    expect(resolveDefaultMergeMethod(["squash", "rebase"])).toBe("squash");
+    expect(resolveDefaultMergeMethod([], "squash")).toBe("merge");
+  });
+});

apps/web/src/components/pull-requests/pullRequests.logic.ts

@@ -1328,15 +1328,28 @@ export const PULL_REQUEST_MERGE_METHOD_LABELS: Readonly<Record<PullRequestMergeM
   rebase: "Rebase and merge",
 };
 
+/** The one word the Merge button itself wears for each method. */
+export const PULL_REQUEST_MERGE_METHOD_WORDS: Readonly<Record<PullRequestMergeMethod, string>> = {
+  merge: "Merge",
+  squash: "Squash",
+  rebase: "Rebase",
+};
+
 /**
- * The method the Merge button runs without being asked. The repository lists
- * what it allows in its own order and the first one is its default; a host
- * that reports nothing still gets a plain merge offered, and refuses it itself
- * if it really is off.
+ * The method the Merge button runs without being asked: the one last used on
+ * this repository while the repository still allows it, the way the host's own
+ * site remembers a choice. Before any choice, the repository lists what it
+ * allows in its own order and the first one is its default; a host that reports
+ * nothing still gets a plain merge offered, and refuses it itself if it really
+ * is off.
  */
 export function resolveDefaultMergeMethod(
   mergeMethods: readonly PullRequestMergeMethod[],
+  remembered: PullRequestMergeMethod | null = null,
 ): PullRequestMergeMethod {
+  if (remembered !== null && mergeMethods.includes(remembered)) {
+    return remembered;
+  }
   return mergeMethods[0] ?? "merge";
 }