Add resource hints for default templates location

Closes gh-31310

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/template/TemplateRuntimeHints.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.template;
+
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
+
+/**
+ * {@link RuntimeHintsRegistrar} for default template location.
+ *
+ * @author Stephane Nicoll
+ */
+class TemplateRuntimeHints implements RuntimeHintsRegistrar {
+
+	@Override
+	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		hints.resources().registerPatternIfPresent(classLoader, "templates", (hint) -> hint.includes("templates/*"));
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring/aot.factories

@@ -0,0 +1,2 @@
+org.springframework.aot.hint.RuntimeHintsRegistrar=\
+org.springframework.boot.autoconfigure.template.TemplateRuntimeHints

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/template/TemplateRuntimeHintsTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2012-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.template;
+
+import java.util.List;
+import java.util.function.Predicate;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
+import org.springframework.beans.factory.aot.AotFactoriesLoader;
+import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.boot.test.context.FilteredClassLoader;
+import org.springframework.core.io.ClassPathResource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link TemplateRuntimeHints}.$
+ *
+ * @author Stephane Nicoll
+ */
+class TemplateRuntimeHintsTests {
+
+	public static final Predicate<RuntimeHints> TEST_PREDICATE = RuntimeHintsPredicates.resource()
+			.forResource("templates/something/hello.html");
+
+	@Test
+	void templateRuntimeHintsIsRegistered() {
+		List<RuntimeHintsRegistrar> registrar = new AotFactoriesLoader(new DefaultListableBeanFactory())
+				.load(RuntimeHintsRegistrar.class);
+		assertThat(registrar).anyMatch(TemplateRuntimeHints.class::isInstance);
+	}
+
+	@Test
+	void contributeWhenTemplateLocationExists() {
+		RuntimeHints runtimeHints = contribute(getClass().getClassLoader());
+		assertThat(TEST_PREDICATE.test(runtimeHints)).isTrue();
+	}
+
+	@Test
+	void contributeWhenTemplateLocationDoesNotExist() {
+		FilteredClassLoader classLoader = new FilteredClassLoader(new ClassPathResource("templates"));
+		RuntimeHints runtimeHints = contribute(classLoader);
+		assertThat(TEST_PREDICATE.test(runtimeHints)).isFalse();
+	}
+
+	private RuntimeHints contribute(ClassLoader classLoader) {
+		RuntimeHints runtimeHints = new RuntimeHints();
+		new TemplateRuntimeHints().registerHints(runtimeHints, classLoader);
+		return runtimeHints;
+	}
+
+}