[JVM-Packages] Auto-detection of MUSL is replaced by system properties (#7921)

This PR removes auto-detection of MUSL-based Linux systems in favor of system properties the user can set to configure a specific path for a native library.

jvm-packages/xgboost4j/src/test/java/ml/dmlc/xgboost4j/java/LibraryPathProviderTest.java

@@ -0,0 +1,61 @@
+/*
+ Copyright (c) 2014 by Contributors
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+package ml.dmlc.xgboost4j.java;
+
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+import static junit.framework.TestCase.assertTrue;
+import static ml.dmlc.xgboost4j.java.NativeLibLoader.Arch.X86_64;
+import static ml.dmlc.xgboost4j.java.NativeLibLoader.LibraryPathProvider.getLibraryPathFor;
+import static ml.dmlc.xgboost4j.java.NativeLibLoader.OS.LINUX;
+
+public class LibraryPathProviderTest {
+
+  @Test
+  public void testLibraryPathProviderUsesOsAndArchToResolvePath() {
+    String libraryPath = getLibraryPathFor(LINUX, X86_64, "someLibrary");
+
+    assertTrue(libraryPath.startsWith("/lib/linux/x86_64/"));
+  }
+
+  @Test
+  public void testLibraryPathProviderUsesPropertyValueForPathIfPresent() {
+    String propertyName = "xgboostruntime.native.library";
+
+    executeAndRestoreProperty(propertyName, () -> {
+      System.setProperty(propertyName, "/my/custom/path/to/my/library");
+      String libraryPath = getLibraryPathFor(LINUX, X86_64, "library");
+
+      assertEquals("/my/custom/path/to/my/library", libraryPath);
+    });
+  }
+
+  private static void executeAndRestoreProperty(String propertyName, Runnable action) {
+    String oldValue = System.getProperty(propertyName);
+
+    try {
+      action.run();
+    } finally {
+      if (oldValue != null) {
+        System.setProperty(propertyName, oldValue);
+      } else {
+        System.clearProperty(propertyName);
+      }
+    }
+  }
+
+}

jvm-packages/xgboost4j/src/test/java/ml/dmlc/xgboost4j/java/OsDetectionTest.java

@@ -16,10 +16,8 @@
 package ml.dmlc.xgboost4j.java;
 
 import ml.dmlc.xgboost4j.java.NativeLibLoader.OS;
-import org.junit.Rule;
 import org.junit.Test;
 import org.junit.experimental.runners.Enclosed;
-import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 import org.junit.runners.Parameterized.Parameters;
@@ -40,12 +38,12 @@ public class OsDetectionTest {
   private static final String OS_NAME_PROPERTY = "os.name";
 
   @RunWith(Parameterized.class)
-  public static class ParameterizedOSDetectionTest {
+  public static class SupportedOSDetectionTest {
 
     private final String osNameValue;
     private final OS expectedOS;
 
-    public ParameterizedOSDetectionTest(String osNameValue, OS expectedOS) {
+    public SupportedOSDetectionTest(String osNameValue, OS expectedOS) {
       this.osNameValue = osNameValue;
       this.expectedOS = expectedOS;
     }
@@ -70,32 +68,7 @@ public class OsDetectionTest {
     }
   }
 
-  public static class NonParameterizedOSDetectionTest {
-
-    @Rule
-    public TemporaryFolder folder = new TemporaryFolder();
-
-    @Test
-    public void testForRegularLinux() throws Exception {
-      setMappedFilesBaseDir(folder.getRoot().toPath());
-      folder.newFile("ld-2.23.so");
-
-      executeAndRestoreProperty(() -> {
-        System.setProperty(OS_NAME_PROPERTY, "linux");
-        assertSame(detectOS(), LINUX);
-      });
-    }
-
-    @Test
-    public void testForMuslBasedLinux() throws Exception {
-      setMappedFilesBaseDir(folder.getRoot().toPath());
-      folder.newFile("ld-musl-x86_64.so.1");
-
-      executeAndRestoreProperty(() -> {
-        System.setProperty(OS_NAME_PROPERTY, "linux");
-        assertSame(detectOS(), LINUX_MUSL);
-      });
-    }
+  public static class UnsupportedOSDetectionTest {
 
     @Test
     public void testUnsupportedOs() {