Support `.` and `_` binder prefix joins

Update RelaxedDataBinder so that both `.` and `_` are considered in
getPropertyValuesForNamePrefix(...).

With Spring Boot 1.2.5 binding environment variables of the form
`FOO_BAR_BAZ` to `@ConfigurationProperties(prefix="foo-bar")` objects
worked thanks to a happy accident. When `PropertySourcesPropertyValues`
processed a non enumerable `PropertySource` it called the resolver
with a property name `FOO_BAR.BAZ`. A `SystemEnvironmentPropertySource`
will replace `.` with `_` and hence find a value.

Commit 1abd0879 updated non enumerable processing such that the resolver
was never called.

Replicating the problem is quite involved as you need to ensure that you
have both a SystemEnvironmentPropertySource and a non-enumerable
property source (e.g. RandomPropertySource). A test has been added to
PropertiesConfigurationFactoryTests which passes on 1.2.5, fails on
1.2.6 and passes again following this commit.

Fixes gh-4045

spring-boot/src/main/java/org/springframework/boot/bind/RelaxedDataBinder.java

@@ -201,11 +201,15 @@ public class RelaxedDataBinder extends DataBinder {
 		MutablePropertyValues rtn = new MutablePropertyValues();
 		for (PropertyValue value : propertyValues.getPropertyValues()) {
 			String name = value.getName();
-			for (String candidate : new RelaxedNames(this.namePrefix)) {
-				if (name.startsWith(candidate)) {
-					name = name.substring(candidate.length());
-					if (!(this.ignoreNestedProperties && name.contains("."))) {
-						rtn.add(name, value.getValue());
+			for (String prefix : new RelaxedNames(stripLastDot(this.namePrefix))) {
+				for (String separator : new String[] { ".", "_" }) {
+					String candidate = (StringUtils.hasLength(prefix) ? prefix
+							+ separator : prefix);
+					if (name.startsWith(candidate)) {
+						name = name.substring(candidate.length());
+						if (!(this.ignoreNestedProperties && name.contains("."))) {
+							rtn.add(name, value.getValue());
+						}
 					}
 				}
 			}
@@ -213,6 +217,13 @@ public class RelaxedDataBinder extends DataBinder {
 		return rtn;
 	}
 
+	private String stripLastDot(String string) {
+		if (StringUtils.hasLength(string) && string.endsWith(".")) {
+			string = string.substring(0, string.length() - 1);
+		}
+		return string;
+	}
+
 	private PropertyValue modifyProperty(BeanWrapper target, PropertyValue propertyValue) {
 		String name = propertyValue.getName();
 		String normalizedName = normalizePath(target, name);

spring-boot/src/test/java/org/springframework/boot/bind/PropertiesConfigurationFactoryTests.java

@@ -17,13 +17,17 @@
 package org.springframework.boot.bind;
 
 import java.io.IOException;
+import java.util.Collections;
 
 import javax.validation.Validation;
 import javax.validation.constraints.NotNull;
 
 import org.junit.Test;
 import org.springframework.beans.NotWritablePropertyException;
+import org.springframework.boot.context.config.RandomValuePropertySource;
 import org.springframework.context.support.StaticMessageSource;
+import org.springframework.core.env.MutablePropertySources;
+import org.springframework.core.env.SystemEnvironmentPropertySource;
 import org.springframework.core.io.ByteArrayResource;
 import org.springframework.core.io.support.PropertiesLoaderUtils;
 import org.springframework.validation.BindException;
@@ -110,6 +114,21 @@ public class PropertiesConfigurationFactoryTests {
 		assertEquals("blah", foo.bar);
 	}
 
+	@Test
+	public void testBindWithDashPrefix() throws Exception {
+		// gh-4045
+		this.targetName = "foo-bar";
+		MutablePropertySources propertySources = new MutablePropertySources();
+		propertySources.addLast(new SystemEnvironmentPropertySource("systemEnvironment",
+				Collections.<String, Object>singletonMap("FOO_BAR_NAME", "blah")));
+		propertySources.addLast(new RandomValuePropertySource("random"));
+		setupFactory();
+		this.factory.setPropertySources(propertySources);
+		this.factory.afterPropertiesSet();
+		Foo foo = this.factory.getObject();
+		assertEquals("blah", foo.name);
+	}
+
 	private Foo createFoo(final String values) throws Exception {
 		setupFactory();
 		return bindFoo(values);