Improve error message when spring.config.import fails to resolve

Update `StandardConfigDataLocationResolver` to give a better error
message when a location cannot be resolved. Prior to this commit, a
location with a misspelling in the prefix would only give an error
about the file extension being not known.

Fixes gh-36243

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -69,17 +69,17 @@ class ConfigDataLocationResolvers {
 	@SuppressWarnings("rawtypes")
 	private List<ConfigDataLocationResolver<?>> reorder(List<ConfigDataLocationResolver> resolvers) {
 		List<ConfigDataLocationResolver<?>> reordered = new ArrayList<>(resolvers.size());
-		StandardConfigDataLocationResolver resourceResolver = null;
+		ConfigDataLocationResolver<?> standardConfigDataLocationResolver = null;
 		for (ConfigDataLocationResolver<?> resolver : resolvers) {
-			if (resolver instanceof StandardConfigDataLocationResolver configDataLocationResolver) {
-				resourceResolver = configDataLocationResolver;
+			if (resolver instanceof StandardConfigDataLocationResolver) {
+				standardConfigDataLocationResolver = resolver;
 			}
 			else {
 				reordered.add(resolver);
 			}
 		}
-		if (resourceResolver != null) {
-			reordered.add(resourceResolver);
+		if (standardConfigDataLocationResolver != null) {
+			reordered.add(standardConfigDataLocationResolver);
 		}
 		return Collections.unmodifiableList(reordered);
 	}

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

@@ -45,6 +45,7 @@
 import org.springframework.core.log.LogMessage;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
+import org.springframework.util.ResourceUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -231,8 +232,17 @@ private Set<StandardConfigDataReference> getReferencesForFile(ConfigDataLocation
 		if (configDataLocation.isOptional()) {
 			return Collections.emptySet();
 		}
-		throw new IllegalStateException("File extension is not known to any PropertySourceLoader. "
-				+ "If the location is meant to reference a directory, it must end in '/' or File.separator");
+		if (configDataLocation.hasPrefix(PREFIX) || configDataLocation.hasPrefix(ResourceUtils.FILE_URL_PREFIX)
+				|| configDataLocation.hasPrefix(ResourceUtils.CLASSPATH_URL_PREFIX)
+				|| configDataLocation.toString().indexOf(':') == -1) {
+			throw new IllegalStateException("File extension is not known to any PropertySourceLoader. "
+					+ "If the location is meant to reference a directory, it must end in '/' or File.separator");
+		}
+		throw new IllegalStateException(
+				"Incorrect ConfigDataLocationResolver chosen or file extension is not known to any PropertySourceLoader. "
+						+ "If the location is meant to reference a directory, it must end in '/' or File.separator. "
+						+ "The location is being resolved using the StandardConfigDataLocationResolver, "
+						+ "check the location prefix if a different resolver is expected");
 	}
 
 	private String getLoadableFileExtension(PropertySourceLoader loader, String file) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 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.
@@ -99,6 +99,16 @@ void resolveWhenLocationIsFileAndNoMatchingLoaderThrowsException() {
 			.satisfies((ex) -> assertThat(ex.getCause()).hasMessageStartingWith("File extension is not known"));
 	}
 
+	@Test
+	void resolveWhenLocationHasUnknownPrefixAndNoMatchingLoaderThrowsException() {
+		ConfigDataLocation location = ConfigDataLocation
+			.of("typo:src/test/resources/configdata/properties/application.unknown");
+		assertThatIllegalStateException().isThrownBy(() -> this.resolver.resolve(this.context, location))
+			.withMessageStartingWith("Unable to load config data from")
+			.satisfies((ex) -> assertThat(ex.getCause()).hasMessageStartingWith(
+					"Incorrect ConfigDataLocationResolver chosen or file extension is not known to any PropertySourceLoader"));
+	}
+
 	@Test
 	void resolveWhenLocationWildcardIsSpecifiedForClasspathLocationThrowsException() {
 		ConfigDataLocation location = ConfigDataLocation.of("classpath*:application.properties");