fix: test:changed --land: dist counts as fresh when it predates the rebase

packages/ui/tests/dist-fresh.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from "bun:test";
+import { distStale } from "../../../scripts/dist-fresh";
+
+// The land gate decides whether to rebuild `dist` before it tests the site. A dist built before the
+// rebase holds old code even when the PR's own diff touches no package file (#591).
+const none = { exists: true, changedAfter: false };
+
+describe("distStale", () => {
+	it("is stale when it does not exist", () => {
+		expect(distStale({ land: false, exists: false, changedAfter: false })).toBe(true);
+	});
+
+	it("a dev run keeps a dist newer than every changed file", () => {
+		expect(distStale({ land: false, ...none })).toBe(false);
+	});
+
+	it("a dev run rebuilds when a changed file is newer than the dist", () => {
+		expect(distStale({ land: false, ...none, changedAfter: true })).toBe(true);
+	});
+
+	it("the land gate always rebuilds: the rebase brings in sources the diff does not list", () => {
+		expect(distStale({ land: true, ...none })).toBe(true);
+	});
+});

scripts/dist-fresh.ts

@@ -0,0 +1,9 @@
+/**
+ * Whether a build output (`packages/ui/dist`, `site/dist`) has to be rebuilt before the site is tested.
+ * A dev run trusts file times: the output is stale when it is missing or a changed file is newer.
+ * The land gate never does: it runs right after a rebase, which brings in sources that are not in the
+ * PR's diff (so no changed file is "newer"), while the output may predate the rebase by hours (#591).
+ */
+export function distStale(o: { land: boolean; exists: boolean; changedAfter: boolean }): boolean {
+	return o.land || !o.exists || o.changedAfter;
+}

scripts/test-changed.ts

@@ -30,6 +30,7 @@
 import { spawnSync } from "node:child_process";
 import { existsSync, readFileSync, statSync } from "node:fs";
 import { join } from "node:path";
+import { distStale } from "./dist-fresh.ts";
 import { lockReachesRuntime, ROOT, select } from "./route-impact.ts";
 import { affected, buildGraph, isSharedComponent, landBudget } from "./test-graph.ts";
 
@@ -203,11 +204,18 @@ if (siteRun) {
 	const siteDist = mtime(join(ROOT, "site/dist/index.html"));
 	const newer = (re: RegExp, than: number) =>
 		changed.some((f) => re.test(f) && mtime(join(ROOT, f)) > than);
-	const pkgStale = !pkgDist || newer(/^packages\/ui\/(src|scripts|package\.json)/, pkgDist);
+	const pkgStale = distStale({
+		land,
+		exists: pkgDist > 0,
+		changedAfter: newer(/^packages\/ui\/(src|scripts|package\.json)/, pkgDist),
+	});
 	const siteStale =
-		!siteDist ||
 		pkgStale ||
-		newer(/^site\/(src|public|astro\.config\.mjs|package\.json)/, siteDist);
+		distStale({
+			land,
+			exists: siteDist > 0,
+			changedAfter: newer(/^site\/(src|public|astro\.config\.mjs|package\.json)/, siteDist),
+		});
 	// A build is ~75 s (package 17 s + site 58 s), more than the whole 60 s dev budget: only the land gate
 	// builds. A dev run uses `site/dist` when it is fresh, and says so when it cannot.
 	if ((pkgStale || siteStale) && !land) {