Ignore file entries in META-INF/versions of multi-release jar

Fixes gh-41001

Author: wilkinsona

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/jar/MetaInfVersionsInfo.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.
@@ -82,15 +82,17 @@ static MetaInfVersionsInfo get(int size, IntFunction<ZipContent.Entry> entries)
 			if (contentEntry.hasNameStartingWith(META_INF_VERSIONS) && !contentEntry.isDirectory()) {
 				String name = contentEntry.getName();
 				int slash = name.indexOf('/', META_INF_VERSIONS.length());
-				String version = name.substring(META_INF_VERSIONS.length(), slash);
-				try {
-					int versionNumber = Integer.parseInt(version);
-					if (versionNumber >= NestedJarFile.BASE_VERSION) {
-						versions.add(versionNumber);
+				if (slash > -1) {
+					String version = name.substring(META_INF_VERSIONS.length(), slash);
+					try {
+						int versionNumber = Integer.parseInt(version);
+						if (versionNumber >= NestedJarFile.BASE_VERSION) {
+							versions.add(versionNumber);
+						}
+					}
+					catch (NumberFormatException ex) {
+						// Ignore
 					}
-				}
-				catch (NumberFormatException ex) {
-					// Ignore
 				}
 			}
 		}

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/MetaInfVersionsInfoTests.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.
@@ -72,6 +72,20 @@ void getWhenHasNoEntriesReturnsNone() {
 		assertThat(info).isSameAs(MetaInfVersionsInfo.NONE);
 	}
 
+	@Test
+	void toleratesUnexpectedFileEntryInMetaInfVersions() {
+		List<ZipContent.Entry> entries = new ArrayList<>();
+		entries.add(mockEntry("META-INF/"));
+		entries.add(mockEntry("META-INF/MANIFEST.MF"));
+		entries.add(mockEntry("META-INF/versions/"));
+		entries.add(mockEntry("META-INF/versions/unexpected"));
+		entries.add(mockEntry("META-INF/versions/9/"));
+		entries.add(mockEntry("META-INF/versions/9/Foo.class"));
+		MetaInfVersionsInfo info = MetaInfVersionsInfo.get(entries.size(), entries::get);
+		assertThat(info.versions()).containsExactly(9);
+		assertThat(info.directories()).containsExactly("META-INF/versions/9/");
+	}
+
 	private ZipContent.Entry mockEntry(String name) {
 		ZipContent.Entry entry = mock(ZipContent.Entry.class);
 		given(entry.getName()).willReturn(name);