Control: flashMessage() does not create the template

In the most typical flow - flashMessage() followed by redirect() - the template
was created just to be thrown away, which builds a whole Latte\Engine instance.
The messages are written to the session first and into the template only if it
already exists; a template created later gets them from the template factory,
which reads the flashes from the session on its own.

Author: dg

docs/internals/templates.md

@@ -42,6 +42,12 @@ the default. `TemplateFactory::createTemplate` instantiates it around a fresh La
 engine and injects the default variables (`user`, `baseUrl`, `basePath`, `flashes`,
 `control`, `presenter`).
 
+**`flashes` depends on this injection.** `Control::flashMessage()` writes the
+message to the flash session and into the template only if the template already
+exists; it never creates one. A template created later gets the messages solely
+from the factory, which reads them from the flash session, so a custom
+`TemplateFactory` has to inject `flashes` the same way.
+
 ## `#[TemplateVariable]`
 
 At `sendTemplate`, `completeTemplate()` copies every `#[TemplateVariable]` property

src/Application/UI/Control.php

@@ -104,10 +104,14 @@ public function flashMessage(string|\stdClass|\Stringable $message, string $type
 			'message' => $message,
 			'type' => $type,
 		];
-		$messages = $this->getPresenter()->getFlashSession()->get($id);
+		$session = $this->getPresenter()->getFlashSession();
+		$messages = $session->get($id);
 		$messages[] = $flash;
-		$this->getTemplate()->flashes = $messages;
-		$this->getPresenter()->getFlashSession()->set($id, $messages);
+		$session->set($id, $messages);
+		if (isset($this->template)) { // a not-yet-created template gets flashes injected by the template factory
+			$this->template->flashes = $messages;
+		}
+
 		return $flash;
 	}
 

tests/UI/Presenter.flashMessage.phpt

@@ -142,7 +142,7 @@ test('multiple flash messages are stored', function () {
 });
 
 
-test('flash message is available in template', function () {
+test('flash message is written to an already created template', function () {
 	$messages = [];
 	$sessionSection = Mockery::mock(Http\SessionSection::class);
 	$sessionSection->shouldReceive('get')->andReturnUsing(function () use (&$messages) {
@@ -172,6 +172,45 @@ test('flash message is available in template', function () {
 
 	$presenter->run(new Application\Request('Test', 'GET', ['action' => 'default']));
 
+	$template = $presenter->getTemplate();
+	$presenter->flashMessage('Template message');
+
+	Assert::count(1, $template->flashes);
+	Assert::same('Template message', $template->flashes[0]->message);
+});
+
+
+test('flash message is injected into a template created later', function () {
+	$messages = [];
+	$sessionSection = Mockery::mock(Http\SessionSection::class);
+	$sessionSection->shouldReceive('get')->andReturnUsing(function () use (&$messages) {
+		return $messages;
+	});
+	$sessionSection->shouldReceive('set')->andReturnUsing(function ($id, $value) use (&$messages) {
+		$messages = $value;
+	});
+
+	$session = Mockery::mock(Http\Session::class);
+	$session->shouldReceive('getSection')->andReturn($sessionSection);
+	$session->shouldReceive('hasSection')->andReturn(true);
+
+	$latte = Mockery::mock(Latte\Engine::class);
+	$latte->shouldIgnoreMissing();
+	$latteFactory = Mockery::mock(Nette\Bridges\ApplicationLatte\LatteFactory::class);
+	$latteFactory->shouldReceive('create')->andReturn($latte);
+	$templateFactory = new Nette\Bridges\ApplicationLatte\TemplateFactory($latteFactory);
+
+	$presenter = new TestPresenter;
+	$presenter->injectPrimary(
+		new Http\Request(new Http\UrlScript),
+		new Http\Response,
+		session: $session,
+		templateFactory: $templateFactory,
+	);
+	$presenter->autoCanonicalize = false;
+
+	$presenter->run(new Application\Request('Test', 'GET', ['action' => 'default']));
+
 	$presenter->flashMessage('Template message');
 
 	$template = $presenter->getTemplate();