Add placeholder resolution to @PropertySource processing

Previously the core Spring processing of @PropertySource would
resolve placeholders in the location attribute, but the pre-loading
of the property source by Spring Boot didn't do that. Now implemented
using Environment.resolvePlaceholders() (N.B. at a time when the only
Environment entries available are system properties and OS env vars).

E.g.

	@Configuration
	@PropertySource("classpath:/${source.location}.properties")
	protected static class WithPropertySourcePlaceholders {
           ...
	}

spring-boot/src/main/java/org/springframework/boot/config/ConfigFileApplicationListener.java

@@ -360,11 +360,9 @@ public class ConfigFileApplicationListener implements
 			candidates.add(LOCATION_VARIABLE);
 			// @PropertySource annotation locations go last here (eventually highest
 			// priority). This unfortunately isn't the same semantics as @PropertySource
-			// in
-			// Spring and it's hard to change that (so the property source gets added
-			// again in
-			// last position by Spring later in the cycle).
-			addLoadCandidatesFromAnnotations(resourceLoader, candidates);
+			// in Spring and it's hard to change that (so the property source gets added
+			// again in last position by Spring later in the cycle).
+			addLoadCandidatesFromAnnotations(environment, resourceLoader, candidates);
 			this.candidates = new ArrayList<String>(candidates);
 			Collections.reverse(this.candidates);
 		}
@@ -382,11 +380,13 @@ public class ConfigFileApplicationListener implements
 			}
 		}
 
-		private void addLoadCandidatesFromAnnotations(ResourceLoader resourceLoader,
+		private void addLoadCandidatesFromAnnotations(
+				ConfigurableEnvironment environment, ResourceLoader resourceLoader,
 				Set<String> candidates) {
 			for (String location : ConfigFileApplicationListener.this.annotations
 					.getLocations()) {
-				Resource resource = resourceLoader.getResource(location);
+				Resource resource = resourceLoader.getResource(environment
+						.resolvePlaceholders(location));
 				if (!ConfigFileApplicationListener.this.annotations
 						.ignoreResourceNotFound(location) && !resource.exists()) {
 					throw new IllegalStateException("Resource not found: " + location);

spring-boot/src/test/java/org/springframework/boot/config/ConfigFileApplicationListenerTests.java

@@ -272,6 +272,22 @@ public class ConfigFileApplicationListenerTests {
 		context.close();
 	}
 
+	@Test
+	public void propertySourceAnnotationWithPlaceholder() throws Exception {
+		EnvironmentTestUtils.addEnvironment(this.environment,
+				"source.location:specificlocation");
+		SpringApplication application = new SpringApplication(
+				WithPropertySourcePlaceholders.class);
+		application.setEnvironment(this.environment);
+		application.setWebEnvironment(false);
+		ConfigurableApplicationContext context = application.run();
+		String property = context.getEnvironment().getProperty("my.property");
+		assertThat(property, equalTo("fromspecificlocation"));
+		assertNotNull(context.getEnvironment().getPropertySources()
+				.get("classpath:/specificlocation.properties"));
+		context.close();
+	}
+
 	@Test
 	public void propertySourceAnnotationWithName() throws Exception {
 		SpringApplication application = new SpringApplication(
@@ -376,6 +392,12 @@ public class ConfigFileApplicationListenerTests {
 
 	}
 
+	@Configuration
+	@PropertySource("classpath:/${source.location}.properties")
+	protected static class WithPropertySourcePlaceholders {
+
+	}
+
 	@Configuration
 	@PropertySource(value = "classpath:/specificlocation.properties", name = "foo")
 	protected static class WithPropertySourceAndName {