Rethrow ConverterNotFoundException when possible

Update `BindConverter` to throw the first `ConversionFailedException`
rather than always throwing `ConverterNotFoundException`.

See gh-27028

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/BindConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -34,7 +34,9 @@
 import org.springframework.boot.convert.ApplicationConversionService;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.convert.ConversionException;
+import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.ConverterNotFoundException;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.ConditionalGenericConverter;
 import org.springframework.core.convert.support.GenericConversionService;
@@ -157,17 +159,20 @@ public <T> T convert(Object source, Class<T> targetType) {
 
 		@Override
 		public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
-			for (int i = 0; i < this.delegates.size() - 1; i++) {
+			ConversionException failure = null;
+			for (ConversionService delegate : this.delegates) {
 				try {
-					ConversionService delegate = this.delegates.get(i);
 					if (delegate.canConvert(sourceType, targetType)) {
 						return delegate.convert(source, sourceType, targetType);
 					}
 				}
 				catch (ConversionException ex) {
+					if (failure == null && ex instanceof ConversionFailedException) {
+						failure = ex;
+					}
 				}
 			}
-			return this.delegates.get(this.delegates.size() - 1).convert(source, sourceType, targetType);
+			throw (failure != null) ? failure : new ConverterNotFoundException(sourceType, targetType);
 		}
 
 	}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/bind/BindConverterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -30,6 +30,7 @@
 import org.springframework.beans.PropertyEditorRegistry;
 import org.springframework.boot.convert.ApplicationConversionService;
 import org.springframework.core.ResolvableType;
+import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.ConverterNotFoundException;
 import org.springframework.core.convert.TypeDescriptor;
@@ -183,6 +184,14 @@ void fallsBackToApplicationConversionService() {
 		assertThat(result.getSeconds()).isEqualTo(10);
 	}
 
+	@Test // gh-27028
+	void convertWhenConversionFailsThrowsConversionFailedExceptionRatherThanConverterNotFoundException() {
+		BindConverter bindConverter = BindConverter.get(ApplicationConversionService.getSharedInstance(), null);
+		assertThatExceptionOfType(ConversionFailedException.class)
+				.isThrownBy(() -> bindConverter.convert("com.example.Missing", ResolvableType.forClass(Class.class)))
+				.withRootCauseInstanceOf(ClassNotFoundException.class);
+	}
+
 	private BindConverter getPropertyEditorOnlyBindConverter(
 			Consumer<PropertyEditorRegistry> propertyEditorInitializer) {
 		return BindConverter.get(new ThrowingConversionService(), propertyEditorInitializer);