List valid values in failure analysis for enum binding failure

Closes gh-11771

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/diagnostics/analyzer/BindFailureAnalyzer.java

@@ -16,12 +16,19 @@
 
 package org.springframework.boot.diagnostics.analyzer;
 
+import java.util.Collection;
+import java.util.Collections;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 import org.springframework.boot.context.properties.bind.BindException;
 import org.springframework.boot.context.properties.bind.UnboundConfigurationPropertiesException;
 import org.springframework.boot.context.properties.bind.validation.BindValidationException;
 import org.springframework.boot.context.properties.source.ConfigurationProperty;
 import org.springframework.boot.diagnostics.AbstractFailureAnalyzer;
 import org.springframework.boot.diagnostics.FailureAnalysis;
+import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.util.StringUtils;
 
 /**
@@ -46,7 +53,7 @@ class BindFailureAnalyzer extends AbstractFailureAnalyzer<BindException> {
 
 	private FailureAnalysis analyzeGenericBindException(BindException cause) {
 		StringBuilder description = new StringBuilder(
-				String.format("Binding to target %s failed:%n", cause.getTarget()));
+				String.format("%s:%n", cause.getMessage()));
 		ConfigurationProperty property = cause.getProperty();
 		buildDescription(description, property);
 		description.append(String.format("%n    Reason: %s", getMessage(cause)));
@@ -71,8 +78,29 @@ class BindFailureAnalyzer extends AbstractFailureAnalyzer<BindException> {
 	}
 
 	private FailureAnalysis getFailureAnalysis(Object description, BindException cause) {
-		return new FailureAnalysis(description.toString(),
-				"Update your application's configuration", cause);
+		StringBuilder message = new StringBuilder(
+				"Update your application's configuration");
+		Collection<String> validValues = findValidValues(cause);
+		if (!validValues.isEmpty()) {
+			message.append(String.format(". The following values are valid:%n"));
+			validValues
+					.forEach((value) -> message.append(String.format("%n    %s", value)));
+		}
+		return new FailureAnalysis(description.toString(), message.toString(), cause);
+	}
+
+	private Collection<String> findValidValues(BindException ex) {
+		ConversionFailedException conversionFailure = findCause(ex,
+				ConversionFailedException.class);
+		if (conversionFailure != null) {
+			Object[] enumConstants = conversionFailure.getTargetType().getType()
+					.getEnumConstants();
+			if (enumConstants != null) {
+				return Stream.of(enumConstants).map(Object::toString)
+						.collect(Collectors.toCollection(TreeSet::new));
+			}
+		}
+		return Collections.emptySet();
 	}
 
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/diagnostics/analyzer/BindFailureAnalyzerTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.diagnostics.analyzer;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import javax.validation.constraints.Min;
 
@@ -67,6 +68,15 @@ public class BindFailureAnalyzerTests {
 				"Could not resolve placeholder 'BAR' in value \"${BAR}\""));
 	}
 
+	@Test
+	public void bindExceptionForUnknownValueInEnumListsValidValuesInAction() {
+		FailureAnalysis analysis = performAnalysis(EnumFailureConfiguration.class,
+				"test.foo.fruit=apple,strawberry");
+		for (Fruit fruit : Fruit.values()) {
+			assertThat(analysis.getAction()).contains(fruit.name());
+		}
+	}
+
 	private static String failure(String property, String value, String origin,
 			String reason) {
 		return String.format(
@@ -124,6 +134,11 @@ public class BindFailureAnalyzerTests {
 
 	}
 
+	@EnableConfigurationProperties(EnumFailureProperties.class)
+	static class EnumFailureConfiguration {
+
+	}
+
 	@ConfigurationProperties("test.foo")
 	@Validated
 	static class FieldValidationFailureProperties {
@@ -170,4 +185,25 @@ public class BindFailureAnalyzerTests {
 
 	}
 
+	@ConfigurationProperties("test.foo")
+	static class EnumFailureProperties {
+
+		private Set<Fruit> fruit;
+
+		public Set<Fruit> getFruit() {
+			return this.fruit;
+		}
+
+		public void setFruit(Set<Fruit> fruit) {
+			this.fruit = fruit;
+		}
+
+	}
+
+	enum Fruit {
+
+		APPLE, BANANA, ORANGE;
+
+	}
+
 }