Keep the browsed file in the source view route

Browsing the file tree only changed component state, so no file view
was ever a history entry and back left the repository. The path now
travels as a query parameter, since trailing URL segments are already
consumed by the revision.

tests/e2e/repo/asciidoc.spec.ts

@@ -25,8 +25,13 @@ test("open a relative link in the source view", async ({ page }) => {
   const url = page.url();
   await readme.getByRole("link", { name: "the notes" }).click();
 
-  // The link opens the file instead of navigating the app away.
+  // The link opens the file in the source view rather than navigating the
+  // window away, and the file it opened is part of the history.
   await expect(page.getByText("Notes from a sibling file.")).toBeVisible();
+  expect(page.url()).not.toBe(url);
+
+  await page.goBack();
+  await expect(readme.getByText("Alpha section text.")).toBeVisible();
   expect(page.url()).toBe(url);
 });
 
@@ -94,6 +99,54 @@ test("bound the reads of recursive includes", async ({ page }) => {
   expect(blobReads).toBeLessThanOrEqual(260);
 });
 
+test("go back from a file opened in the tree", async ({ page }) => {
+  await page.goto("/inbox");
+  await page.getByRole("link", { name: "asciidoc" }).click();
+
+  const readme = page.locator(".asciidoc");
+  await expect(readme.getByText("Alpha section text.")).toBeVisible();
+  const url = page.url();
+
+  await page.getByText("notes.txt", { exact: true }).click();
+  await expect(page.getByText("Notes from a sibling file.")).toBeVisible();
+  await expect(page).toHaveURL(/\?path=notes\.txt/);
+
+  await page.goBack();
+  await expect(readme.getByText("Alpha section text.")).toBeVisible();
+  expect(page.url()).toBe(url);
+});
+
+test("show the same path at another revision", async ({ page }) => {
+  await page.goto("/inbox");
+  const commit = page.waitForResponse(
+    response => new URL(response.url()).pathname === "/repo_commit",
+  );
+  await page.getByRole("link", { name: "asciidoc" }).click();
+  const { parents } = (await (await commit).json()) as { parents: string[] };
+  const rid = page.url().match(/\/repos\/(rad:[^/?]+)/)?.[1];
+
+  await page.getByText("notes.txt", { exact: true }).click();
+  await expect(page.getByText("Notes from a sibling file.")).toBeVisible();
+
+  // Follow an in-app link to the same file at the previous commit, so the
+  // view is reused with only the revision changed.
+  await page.evaluate(href => {
+    const anchor = document.createElement("a");
+    anchor.href = href;
+    document.body.appendChild(anchor);
+    anchor.click();
+    anchor.remove();
+  }, `/repos/${rid}/home/${parents[0]}?path=notes.txt`);
+
+  await expect(
+    page.getByText("An earlier version of the notes."),
+  ).toBeVisible();
+  await expect(page.getByText("Notes from a sibling file.")).toHaveCount(0);
+
+  await page.goBack();
+  await expect(page.getByText("Notes from a sibling file.")).toBeVisible();
+});
+
 test("sanitize untrusted markup in an AsciiDoc readme", async ({ page }) => {
   await page.goto("/inbox");
   await page.getByRole("link", { name: "asciidoc" }).click();

tests/support/fixtures.ts

@@ -597,6 +597,15 @@ export async function createMarkdownFixture(peer: RadiclePeer) {
 export async function createAsciidocFixture(peer: RadiclePeer) {
   const { repoFolder } = await createRepo(peer, { name: "asciidoc" });
 
+  // An older version of a file, so a test can show the same path at two
+  // revisions.
+  await Fs.writeFile(
+    Path.join(repoFolder, "notes.txt"),
+    "An earlier version of the notes.\n",
+  );
+  await peer.git(["add", "."], { cwd: repoFolder });
+  await peer.git(["commit", "-m", "Add notes"], { cwd: repoFolder });
+
   await Fs.writeFile(
     Path.join(repoFolder, "README.adoc"),
     [