Merge pull request #30456 from candrews

* gh-30456:
  Polish "Make MustacheViewResolver bean back off without Spring MVC"
  Make MustacheViewResolver bean back off without Spring MVC

Closes gh-30456

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mustache/MustacheServletWebConfiguration.java

@@ -18,6 +18,7 @@
 
 import com.samskivert.mustache.Mustache.Compiler;
 
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
@@ -29,6 +30,7 @@
 
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnWebApplication(type = Type.SERVLET)
+@ConditionalOnClass(MustacheViewResolver.class)
 class MustacheServletWebConfiguration {
 
 	@Bean

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/mustache/MustacheAutoConfigurationWithoutWebMvcTests.java

@@ -0,0 +1,45 @@
+/*
+ * 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.mustache;
+
+import com.samskivert.mustache.Mustache;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
+import org.springframework.boot.testsupport.classpath.ClassPathExclusions;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link MustacheAutoConfiguration} without Spring MVC on the class path.
+ *
+ * @author Andy Wilkinson
+ */
+@ClassPathExclusions("spring-webmvc-*.jar")
+class MustacheAutoConfigurationWithoutWebMvcTests {
+
+	@Test
+	void registerBeansForServletAppWithoutMvc() {
+		new WebApplicationContextRunner().withConfiguration(AutoConfigurations.of(MustacheAutoConfiguration.class))
+				.run((context) -> {
+					assertThat(context).hasSingleBean(Mustache.Compiler.class);
+					assertThat(context).hasSingleBean(MustacheResourceTemplateLoader.class);
+				});
+	}
+
+}