Throw exception if classpath*: is used

Update `ConfigFileApplicationListener` to throw a better exception if
`classpath*:` is used as a location.

Closes gh-21168

Author: philwebb

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

@@ -62,6 +62,7 @@
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
+import org.springframework.core.io.support.ResourcePatternResolver;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
@@ -618,6 +619,8 @@ private Set<String> getSearchLocations(String propertyName) {
 				for (String path : asResolvedSet(this.environment.getProperty(propertyName), null)) {
 					if (!path.contains("$")) {
 						path = StringUtils.cleanPath(path);
+						Assert.state(!path.startsWith(ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX),
+								"Classpath wildard patterns cannot be used as a search location");
 						if (!ResourceUtils.isUrl(path)) {
 							path = ResourceUtils.FILE_URL_PREFIX + path;
 						}

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

@@ -63,6 +63,7 @@
 import org.springframework.util.StringUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 /**
  * Tests for {@link ConfigFileApplicationListener}.
@@ -648,6 +649,15 @@ public void absoluteResourceDefaultsToFile() {
 				matchingPropertySource("applicationConfig: [file:" + location.replace(File.separatorChar, '/') + "]"));
 	}
 
+	@Test
+	public void classpathWildcardResourceThrowsException() {
+		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.environment,
+				"spring.config.location=classpath*:override.properties");
+		assertThatIllegalStateException()
+				.isThrownBy(() -> this.initializer.postProcessEnvironment(this.environment, this.application))
+				.withMessage("Classpath wildard patterns cannot be used as a search location");
+	}
+
 	@Test
 	public void propertySourceAnnotation() {
 		SpringApplication application = new SpringApplication(WithPropertySource.class);