Encode Visit Action into Turbo-Action: header

When initiating a `Visit` from an `<a data-turbo-action="...">` element,
encode the Action value into the request's `Turbo-Action:` header.

Similarly, when submitting a `<form data-turbo-action="...">`, encode
the value into the header.

If a `<turbo-frame>` is navigated with an Action, encode the action
along with the `Turbo-Frame:` header.

src/core/drive/form_submission.ts

@@ -160,6 +160,12 @@ export class FormSubmission {
     if (this.requestAcceptsTurboStreamResponse(request)) {
       request.acceptResponseType(StreamMessage.contentType)
     }
+
+    const turboAction = getAttribute("data-turbo-action", this.submitter, this.formElement)
+
+    if (turboAction) {
+      headers["Turbo-Action"] = turboAction
+    }
   }
 
   requestStarted(_request: FetchRequest) {

src/core/drive/visit.ts

@@ -339,6 +339,8 @@ export class Visit implements FetchRequestDelegate {
     if (this.acceptsStreamResponse) {
       request.acceptResponseType(StreamMessage.contentType)
     }
+
+    headers["Turbo-Action"] = this.action
   }
 
   requestStarted() {

src/core/frames/frame_controller.ts

@@ -250,6 +250,10 @@ export class FrameController
     if (this.currentNavigationElement?.hasAttribute("data-turbo-stream")) {
       request.acceptResponseType(StreamMessage.contentType)
     }
+
+    if (this.action) {
+      headers["Turbo-Action"] = this.action
+    }
   }
 
   requestStarted(_request: FetchRequest) {

src/tests/fixtures/form.html

@@ -86,6 +86,11 @@ <h1>Form</h1>
         <input type="submit">
         <button type="submit" name="greeting" id="secondary_submitter" data-turbo-confirm="Are you really sure?" formaction="/__turbo/redirect?path=/src/tests/fixtures/one.html" formmethod="post" value="secondary_submitter">Secondary action</button>
       </form>
+      <form action="/__turbo/redirect" method="post" data-turbo-action="replace">
+        <input type="hidden" name="path" value="/src/tests/fixtures/form.html">
+        <input type="hidden" name="greeting" value="Hello from a replace redirect">
+        <button id="standard-post-form-replace-submit">form[method=post][data-turbo-action="replace"]</button>
+      </form>
     </div>
     <hr>
     <div id="no-action">

src/tests/fixtures/visit.html

@@ -13,6 +13,7 @@
     <section>
       <h1>Visit</h1>
       <p><a id="same-origin-link" href="/src/tests/fixtures/one.html">Same-origin link</a></p>
+      <p><a id="same-origin-link-replace" href="/src/tests/fixtures/one.html" data-turbo-action="replace">Same-origin link replace</a></p>
       <p><a id="same-origin-link-search-params" href="/src/tests/fixtures/one.html?key=value">Same-origin link with ?key=value</a></p>
       <p><a id="sample-response" href="/src/tests/fixtures/one.html">Sample response</a></p>
       <p><a id="same-page-link" href="/src/tests/fixtures/visit.html">Same page link</a></p>

src/tests/functional/form_submission_tests.ts

@@ -151,6 +151,14 @@ test("test standard POST form submission events", async ({ page }) => {
   await nextEventNamed(page, "turbo:load")
 })
 
+test("test standard POST encodes [data-turbo-action] into Turbo-Action", async ({ page }) => {
+  await page.click("#standard-post-form-replace-submit")
+
+  const { fetchOptions } = await nextEventNamed(page, "turbo:before-fetch-request")
+
+  assert.equal(fetchOptions.headers["Turbo-Action"], "replace", "encodes the action to the Turbo-Action header")
+})
+
 test("test standard POST form submission merges values from both searchParams and body", async ({ page }) => {
   await page.click("#form-action-post-redirect-self-q-b")
   await nextBody(page)

src/tests/functional/frame_tests.ts

@@ -614,13 +614,13 @@ test("test navigating a frame with a form[method=get] that does not redirect sti
 test("test navigating turbo-frame[data-turbo-action=advance] from within pushes URL state", async ({ page }) => {
   await page.click("#add-turbo-action-to-frame")
   await page.click("#link-frame")
+  const { fetchOptions } = await nextEventOnTarget(page, "frame", "turbo:before-fetch-request")
   await nextEventNamed(page, "turbo:load")
 
-  const title = await page.textContent("h1")
-  const frameTitle = await page.textContent("#frame h2")
-
-  assert.equal(title, "Frames")
-  assert.equal(frameTitle, "Frame: Loaded")
+  assert.equal(fetchOptions.headers["Turbo-Frame"], "frame", "encodes Turbo-Frame header")
+  assert.equal(fetchOptions.headers["Turbo-Action"], "advance", "encodes Turbo-Action header")
+  assert.equal(await page.textContent("h1"), "Frames")
+  assert.equal(await page.textContent("#frame h2"), "Frame: Loaded")
   assert.equal(pathname(page.url()), "/src/tests/fixtures/frames/frame.html")
 })
 
@@ -708,15 +708,16 @@ test("test navigating frame with a[data-turbo-action=advance] pushes URL state",
 
 test("test navigating frame with form[method=get][data-turbo-action=advance] pushes URL state", async ({ page }) => {
   await page.click("#form-get-frame-action-advance button")
+  const { fetchOptions } = await nextEventOnTarget(page, "form-get-frame-action-advance", "turbo:before-fetch-request")
   await nextEventNamed(page, "turbo:load")
 
-  const title = await page.textContent("h1")
-  const frameTitle = await page.textContent("#frame h2")
-  const src = (await attributeForSelector(page, "#frame", "src")) ?? ""
+  const src = (await attributeForSelector(page, "#frame", "src")) || ""
 
+  assert.equal(fetchOptions.headers["Turbo-Frame"], "frame", "encodes the frame [id] to the Turbo-Frame header")
+  assert.equal(fetchOptions.headers["Turbo-Action"], "advance", "encodes the action to the Turbo-Action header")
   assert.ok(src.includes("/src/tests/fixtures/frames/frame.html"), "updates src attribute")
-  assert.equal(title, "Frames")
-  assert.equal(frameTitle, "Frame: Loaded")
+  assert.equal(await page.textContent("h1"), "Frames")
+  assert.equal(await page.textContent("#frame h2"), "Frame: Loaded")
   assert.equal(pathname(page.url()), "/src/tests/fixtures/frames/frame.html")
   assert.ok(await hasSelector(page, "#frame[complete]"), "marks the frame as [complete]")
 })

src/tests/functional/visit_tests.ts

@@ -114,6 +114,13 @@ test("test turbo:before-fetch-request event.detail encodes searchParams", async
   assert.ok(url.includes("/src/tests/fixtures/one.html?key=value"))
 })
 
+test("test turbo:before-fetch-request encodes the action", async ({ page }) => {
+  await page.click("#same-origin-link-replace")
+  const { fetchOptions } = await nextEventNamed(page, "turbo:before-fetch-request")
+
+  assert.equal(fetchOptions.headers["Turbo-Action"], "replace", "encodes the action into Turbo-Action")
+})
+
 test("test turbo:before-fetch-response open new site", async ({ page }) => {
   page.evaluate(() =>
     addEventListener(