Merge pull request #49582 from answndud

* gh-49582:
  Polish "Add failure analysis for missing auto-configured MailSender"
  Add failure analysis for missing auto-configured MailSender

Closes gh-49582

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

@@ -0,0 +1,102 @@
+/*
+ * 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 java.util.Map;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.boot.autoconfigure.condition.ConditionEvaluationReport;
+import org.springframework.boot.autoconfigure.condition.ConditionEvaluationReport.ConditionAndOutcome;
+import org.springframework.boot.autoconfigure.condition.ConditionEvaluationReport.ConditionAndOutcomes;
+import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
+import org.springframework.boot.diagnostics.FailureAnalysis;
+import org.springframework.boot.mail.autoconfigure.MailSenderAutoConfiguration.MailSenderCondition;
+import org.springframework.core.Ordered;
+import org.springframework.mail.MailSender;
+
+/**
+ * An {@link AbstractFailureAnalyzer} that improves missing {@link MailSender} guidance
+ * when {@link MailSenderAutoConfiguration} is present but did not match.
+ *
+ * @author MJY (answndud)
+ * @author Andy Wilkinson
+ */
+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 BeanFactory beanFactory;
+
+	NoSuchMailSenderBeanFailureAnalyzer(BeanFactory beanFactory) {
+		this.beanFactory = beanFactory;
+	}
+
+	@Override
+	protected @Nullable FailureAnalysis analyze(Throwable rootFailure, NoSuchBeanDefinitionException cause) {
+		if (!isMissingMailSenderBean(cause)) {
+			return null;
+		}
+		ConditionAndOutcome conditionAndOutcome = findMailSenderConditionOutcome();
+		if (conditionAndOutcome == null || conditionAndOutcome.getOutcome().isMatch()) {
+			return null;
+		}
+		String description = "A MailSender bean could not be found because MailSenderAutoConfiguration "
+				+ "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 @Nullable ConditionAndOutcome findMailSenderConditionOutcome() {
+		ConditionEvaluationReport conditionEvaluationReport = ConditionEvaluationReport.find(this.beanFactory);
+		if (conditionEvaluationReport != null) {
+			Map<String, ConditionAndOutcomes> conditionAndOutcomesBySource = conditionEvaluationReport
+				.getConditionAndOutcomesBySource();
+			ConditionAndOutcomes conditionAndOutcomes = conditionAndOutcomesBySource
+				.get(MailSenderAutoConfiguration.class.getName());
+			if (conditionAndOutcomes != null) {
+				return conditionAndOutcomes.stream()
+					.filter((candidate) -> candidate.getCondition() instanceof MailSenderCondition)
+					.findFirst()
+					.orElse(null);
+			}
+		}
+		return null;
+	}
+
+	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);
+	}
+
+	@Override
+	public int getOrder() {
+		return 0;
+	}
+
+}

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

@@ -0,0 +1,3 @@
+# 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 +1,90 @@
+/*
+ * 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.config.ConfigurableListableBeanFactory;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.diagnostics.FailureAnalysis;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.mail.MailSender;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatException;
+
+/**
+ * Tests for {@link NoSuchMailSenderBeanFailureAnalyzer}.
+ *
+ * @author MJY (answndud)
+ * @author Andy Wilkinson
+ */
+class NoSuchMailSenderBeanFailureAnalyzerTests {
+
+	@Test
+	void analyzeWhenNotNoSuchBeanDefinitionExceptionShouldReturnNull() {
+		new ApplicationContextRunner().withConfiguration(AutoConfigurations.of(MailSenderAutoConfiguration.class))
+			.run((context) -> {
+				ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
+				FailureAnalysis analysis = new NoSuchMailSenderBeanFailureAnalyzer(beanFactory)
+					.analyze(new Exception());
+				assertThat(analysis).isNull();
+			});
+	}
+
+	@Test
+	void analyzeWhenNoSuchBeanDefinitionExceptionForDifferentTypeShouldReturnNull() {
+		new ApplicationContextRunner().withConfiguration(AutoConfigurations.of(MailSenderAutoConfiguration.class))
+			.run((context) -> {
+				ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
+				assertThatException().isThrownBy(() -> context.getBean(String.class)).satisfies((ex) -> {
+					FailureAnalysis analysis = new NoSuchMailSenderBeanFailureAnalyzer(beanFactory).analyze(ex);
+					assertThat(analysis).isNull();
+				});
+			});
+	}
+
+	@Test
+	void analyzeWithoutMailSenderAutoConfigurationShouldReturnNull() {
+		new ApplicationContextRunner().run((context) -> {
+			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
+			assertThatException().isThrownBy(() -> context.getBean(MailSender.class)).satisfies((ex) -> {
+				FailureAnalysis analysis = new NoSuchMailSenderBeanFailureAnalyzer(beanFactory).analyze(ex);
+				assertThat(analysis).isNull();
+			});
+		});
+	}
+
+	@Test
+	void analyzeWhenMailSenderBeanIsMissingAndMailSenderConditionDidNotMatchShouldProvideGuidance() {
+		new ApplicationContextRunner().withConfiguration(AutoConfigurations.of(MailSenderAutoConfiguration.class))
+			.run((context) -> {
+				ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
+				assertThatException().isThrownBy(() -> context.getBean(MailSender.class)).satisfies((ex) -> {
+					FailureAnalysis analysis = new NoSuchMailSenderBeanFailureAnalyzer(beanFactory).analyze(ex);
+					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");
+				});
+			});
+	}
+
+}