Add failure analysis for missing auto-configured MailSender

Signed-off-by: MJY <jmoon0227@gmail.com>

See gh-49582

module/spring-boot-mail/src/main/java/org/springframework/boot/mail/autoconfigure/NoSuchMailSenderBeanFailureAnalyzer.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright 2012-present 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.mail.autoconfigure;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
+import org.springframework.boot.diagnostics.FailureAnalysis;
+import org.springframework.core.Ordered;
+import org.springframework.core.env.Environment;
+import org.springframework.mail.MailSender;
+
+/**
+ * An {@link AbstractFailureAnalyzer} that improves missing {@link MailSender} guidance
+ * when mail auto-configuration is present but not activated.
+ */
+class NoSuchMailSenderBeanFailureAnalyzer extends AbstractFailureAnalyzer<NoSuchBeanDefinitionException>
+		implements Ordered {
+
+	private static final String MAIL_HOST_PROPERTY = "spring.mail.host";
+
+	private static final String MAIL_JNDI_NAME_PROPERTY = "spring.mail.jndi-name";
+
+	private final @Nullable Environment environment;
+
+	NoSuchMailSenderBeanFailureAnalyzer(@Nullable Environment environment) {
+		this.environment = environment;
+	}
+
+	@Override
+	protected @Nullable FailureAnalysis analyze(Throwable rootFailure, NoSuchBeanDefinitionException cause) {
+		if (!isMissingMailSenderBean(cause) || hasMailConfigurationProperty()) {
+			return null;
+		}
+		String description = "A MailSender bean could not be found because Spring Boot mail auto-configuration "
+				+ "did not match. Neither '" + MAIL_HOST_PROPERTY + "' nor '" + MAIL_JNDI_NAME_PROPERTY
+				+ "' is configured.";
+		String action = "Consider configuring '" + MAIL_HOST_PROPERTY + "' or '" + MAIL_JNDI_NAME_PROPERTY
+				+ "' to enable auto-configuration. If you want to use a custom mail sender, define a MailSender "
+				+ "bean in your configuration.";
+		return new FailureAnalysis(description, action, cause);
+	}
+
+	private boolean isMissingMailSenderBean(NoSuchBeanDefinitionException cause) {
+		Class<?> beanType = cause.getBeanType();
+		if (beanType == null && cause.getResolvableType() != null) {
+			beanType = cause.getResolvableType().resolve();
+		}
+		return (beanType != null) && MailSender.class.isAssignableFrom(beanType);
+	}
+
+	private boolean hasMailConfigurationProperty() {
+		return this.environment != null && (this.environment.containsProperty(MAIL_HOST_PROPERTY)
+				|| this.environment.containsProperty(MAIL_JNDI_NAME_PROPERTY));
+	}
+
+	@Override
+	public int getOrder() {
+		return 0;
+	}
+
+}

module/spring-boot-mail/src/main/resources/META-INF/spring.factories

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+# Failure Analyzers
+org.springframework.boot.diagnostics.FailureAnalyzer=\
+org.springframework.boot.mail.autoconfigure.NoSuchMailSenderBeanFailureAnalyzer

module/spring-boot-mail/src/test/java/org/springframework/boot/mail/autoconfigure/NoSuchMailSenderBeanFailureAnalyzerTests.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2012-present 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.mail.autoconfigure;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.boot.diagnostics.FailureAnalysis;
+import org.springframework.core.env.Environment;
+import org.springframework.mail.MailSender;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.mock.env.MockEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link NoSuchMailSenderBeanFailureAnalyzer}.
+ */
+class NoSuchMailSenderBeanFailureAnalyzerTests {
+
+	@Test
+	void analyzeWhenNotNoSuchBeanDefinitionExceptionShouldReturnNull() {
+		assertThat(new NoSuchMailSenderBeanFailureAnalyzer(null).analyze(new Exception())).isNull();
+	}
+
+	@Test
+	void analyzeWhenNoSuchBeanDefinitionExceptionForDifferentTypeShouldReturnNull() {
+		assertThat(
+				new NoSuchMailSenderBeanFailureAnalyzer(null).analyze(new NoSuchBeanDefinitionException(String.class)))
+			.isNull();
+	}
+
+	@Test
+	void analyzeWhenMailHostPropertyIsConfiguredShouldReturnNull() {
+		Environment environment = new MockEnvironment().withProperty("spring.mail.host", "smtp.example.org");
+		assertThat(new NoSuchMailSenderBeanFailureAnalyzer(environment)
+			.analyze(new NoSuchBeanDefinitionException(MailSender.class))).isNull();
+	}
+
+	@Test
+	void analyzeWhenMailJndiNamePropertyIsConfiguredShouldReturnNull() {
+		Environment environment = new MockEnvironment().withProperty("spring.mail.jndi-name", "mail/Session");
+		assertThat(new NoSuchMailSenderBeanFailureAnalyzer(environment)
+			.analyze(new NoSuchBeanDefinitionException(MailSender.class))).isNull();
+	}
+
+	@Test
+	void analyzeWhenMailSenderBeanIsMissingAndNoMailPropertiesAreConfiguredShouldProvideGuidance() {
+		FailureAnalysis analysis = new NoSuchMailSenderBeanFailureAnalyzer(new MockEnvironment())
+			.analyze(new NoSuchBeanDefinitionException(MailSender.class));
+		assertThat(analysis).isNotNull();
+		assertThat(analysis.getDescription())
+			.contains("A MailSender bean could not be found")
+			.contains("spring.mail.host")
+			.contains("spring.mail.jndi-name");
+		assertThat(analysis.getAction())
+			.contains("spring.mail.host")
+			.contains("spring.mail.jndi-name")
+			.contains("MailSender bean");
+	}
+
+	@Test
+	void analyzeWhenJavaMailSenderBeanIsMissingAndNoMailPropertiesAreConfiguredShouldProvideGuidance() {
+		assertThat(new NoSuchMailSenderBeanFailureAnalyzer(new MockEnvironment())
+			.analyze(new NoSuchBeanDefinitionException(JavaMailSender.class))).isNotNull();
+	}
+
+}