swarm-ui, swarm-controller: the review try-out's repo and PR fields offer the repos and PRs to pick

Two read-only routes feed them: GET /api/pulls/repos lists the repos with an
open pull request, and GET /api/pulls?repo=owner/name lists a repo's open
pull requests, highest number first. The page offers the lists through the
browser's own suggestion list and keeps both fields free text, since a run
also works on a merged or closed PR.

frontend/packages/swarm-ui/src/pages/review-tryout/ReviewTryOutPage.tsx

@@ -6,6 +6,10 @@
 // `202 {id}`, and polls `GET .../try-out/{id}` until the run is `done` or
 // `failed`. A run takes a minute or more, so the page says it is running.
 //
+// The repo and PR fields offer the repos that have an open PR and the open PRs
+// of the repo (`GET /api/pulls/repos`, `GET /api/pulls?repo=…`), and stay free
+// text: the run also works on a merged or closed PR.
+//
 // **load the repo's rules** fills the rows from the rules on the repo's default
 // branch (`GET /api/review-classifier/rules`), to run as they are or to edit.
 //
@@ -31,6 +35,7 @@ import {
   repoProblem,
   toBody,
   type ClassificationDraft,
+  type OpenPull,
   type RulesAnswer,
   type TryOutResult as Result,
 } from "./TryOutTypes.js";
@@ -38,6 +43,11 @@ import "./ReviewTryOutPage.css";
 
 const TRY_OUT = "/api/review-classifier/try-out";
 const RULES = "/api/review-classifier/rules";
+const PULL_REPOS = "/api/pulls/repos";
+const PULLS = "/api/pulls";
+// How long the repo field rests before its PRs are fetched, so typing a repo
+// does not ask for the PRs of each prefix of it.
+const PICK_DELAY_MS = 300;
 const POLL_MS = 2000;
 // More classifications than this are not offered a row. It is the try-out
 // endpoint's own cap, which answers a longer list with a 400 that the page
@@ -77,8 +87,68 @@ export function ReviewTryOutPage() {
   );
   const [confirmLoad, setConfirmLoad] = useState(false);
 
+  // What the two fields offer to complete to. The fields stay free text, so a
+  // repo or a PR the lists lack, a merged one say, can still be typed.
+  const [repoChoices, setRepoChoices] = useState<string[]>([]);
+  const [repoChoicesError, setRepoChoicesError] =
+    useState<ProblemDetails | null>(null);
+  const [pulls, setPulls] = useState<OpenPull[]>([]);
+  const [pullsError, setPullsError] = useState<ProblemDetails | null>(null);
+
   const running = starting || runId !== null;
 
+  // The repos with an open PR, read once when the page opens.
+  useEffect(() => {
+    let cancelled = false;
+    void (async () => {
+      try {
+        const res = await fetch(PULL_REPOS);
+        if (cancelled) return;
+        if (!res.ok) {
+          setRepoChoicesError(await readApiError(res));
+          return;
+        }
+        setRepoChoices((await res.json()) as string[]);
+      } catch (e: unknown) {
+        if (!cancelled) setRepoChoicesError({ detail: String(e) });
+      }
+    })();
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  // The open PRs of the repo once it is typed or picked and has stopped
+  // changing. A repo that is not valid yet has no list.
+  useEffect(() => {
+    setPulls([]);
+    setPullsError(null);
+    const target = repo.trim();
+    if (repoProblem(target) !== null) return;
+    let cancelled = false;
+    const timer = setTimeout(() => {
+      void (async () => {
+        try {
+          const res = await fetch(
+            `${PULLS}?repo=${encodeURIComponent(target)}`,
+          );
+          if (cancelled) return;
+          if (!res.ok) {
+            setPullsError(await readApiError(res));
+            return;
+          }
+          setPulls((await res.json()) as OpenPull[]);
+        } catch (e: unknown) {
+          if (!cancelled) setPullsError({ detail: String(e) });
+        }
+      })();
+    }, PICK_DELAY_MS);
+    return () => {
+      cancelled = true;
+      clearTimeout(timer);
+    };
+  }, [repo]);
+
   useEffect(() => {
     if (!running) return;
     setElapsed(0);
@@ -217,6 +287,7 @@ export function ReviewTryOutPage() {
               value={repo}
               placeholder="owner/name"
               onInput={setRepo}
+              suggestions={repoChoices.map((value) => ({ value }))}
             />
             <TextField
               id="tryout-pr"
@@ -224,6 +295,10 @@ export function ReviewTryOutPage() {
               value={pr}
               pattern="[0-9]+"
               onInput={setPr}
+              suggestions={pulls.map((p) => ({
+                value: String(p.number),
+                label: p.title,
+              }))}
             />
             <Button
               onClick={askLoadRules}
@@ -232,6 +307,18 @@ export function ReviewTryOutPage() {
               {loadingRules ? "loading…" : "load the repo's rules"}
             </Button>
           </div>
+          {repoChoicesError ? (
+            <ApiErrorPanel
+              context="the repos with an open PR could not be listed"
+              problem={repoChoicesError}
+            />
+          ) : null}
+          {pullsError ? (
+            <ApiErrorPanel
+              context="the repo's open PRs could not be listed"
+              problem={pullsError}
+            />
+          ) : null}
           {rulesError ? (
             <ApiErrorPanel
               context="the repo's rules could not be loaded"

frontend/packages/swarm-ui/src/pages/review-tryout/TryOutTypes.ts

@@ -34,6 +34,13 @@ export interface RulesAnswer {
   classifications: ClassificationBody[];
 }
 
+/** An open PR, as `GET /api/pulls?repo=…` lists it. */
+export interface OpenPull {
+  number: number;
+  title: string;
+  head_sha?: string;
+}
+
 export type Verdict = "match" | "no-match" | "not-applicable";
 
 export interface TryOutRow {