diff --git a/platform/platform-tests/testSrc/com/intellij/openapi/util/io/CaseSensitivityDetectionTest.java b/platform/platform-tests/testSrc/com/intellij/openapi/util/io/CaseSensitivityDetectionTest.java
index c58a7bc4b632..d20311bbd346 100644
--- a/platform/platform-tests/testSrc/com/intellij/openapi/util/io/CaseSensitivityDetectionTest.java
+++ b/platform/platform-tests/testSrc/com/intellij/openapi/util/io/CaseSensitivityDetectionTest.java
@@ -5,13 +5,17 @@ import com.intellij.openapi.util.SystemInfo;
 import com.intellij.openapi.util.io.FileAttributes.CaseSensitivity;
 import com.intellij.testFramework.rules.TempDirectory;
 import com.intellij.util.io.SuperUserStatus;
+import com.intellij.util.system.OS;
 import org.junit.Rule;
 import org.junit.Test;
 
-import java.io.File;
 import java.io.IOException;
+import java.nio.file.FileAlreadyExistsException;
+import java.nio.file.Files;
+import java.nio.file.Path;
 
 import static com.intellij.openapi.util.io.IoTestUtil.*;
+import static org.assertj.core.api.Assertions.assertThatCode;
 import static org.junit.Assert.*;
 import static org.junit.Assume.assumeTrue;
 
@@ -20,32 +24,29 @@ import static org.junit.Assume.assumeTrue;
 public class CaseSensitivityDetectionTest {
   @Rule public TempDirectory tempDir = new TempDirectory();
 
-  @Test
-  public void windowsFSRootsMustHaveDefaultSensitivity() {
+  @Test public void windowsFSRootsMustHaveDefaultSensitivity() {
     assumeWindows();
 
-    String systemDrive = System.getenv("SystemDrive");  // typically, "C:"
+    var systemDrive = System.getenv("SystemDrive");  // typically, "C:"
     assertNotNull(systemDrive);
-    File root = new File(systemDrive + '\\');
-    CaseSensitivity rootCs = FileSystemUtil.readParentCaseSensitivity(root);
+    var root = Path.of(systemDrive + '\\');
+    var rootCs = FileSystemUtil.readParentCaseSensitivity(root.toFile());
     assertEquals(systemDrive, CaseSensitivity.INSENSITIVE, rootCs);
 
-    String systemRoot = System.getenv("SystemRoot");  // typically, "C:\Windows"
+    var systemRoot = System.getenv("SystemRoot");  // typically, "C:\Windows"
     assertNotNull(systemRoot);
-    File child = new File(systemRoot);
-    assertEquals(root, child.getParentFile());
-    assertEquals(systemRoot, rootCs, FileSystemUtil.readParentCaseSensitivity(child));
+    var child = Path.of(systemRoot);
+    assertEquals(root, child.getParent());
+    assertEquals(systemRoot, rootCs, FileSystemUtil.readParentCaseSensitivity(child.toFile()));
   }
 
-  @Test
-  public void wslRootsMustBeCaseSensitive() {
-    String name = assumeWorkingWslDistribution();
-    String root = "\\\\wsl$\\" + name;
-    assertEquals(root, CaseSensitivity.SENSITIVE, FileSystemUtil.readParentCaseSensitivity(new File(root)));
+  @Test public void wslRootsMustBeCaseSensitive() {
+    var name = assumeWorkingWslDistribution();
+    var root = Path.of("\\\\wsl$\\" + name);
+    assertEquals(root.toString(), CaseSensitivity.SENSITIVE, FileSystemUtil.readParentCaseSensitivity(root.toFile()));
   }
 
-  @Test
-  public void caseSensitivityChangesUnderWindowsMustBeReReadCorrectly() throws IOException {
+  @Test public void caseSensitivityChangesUnderWindowsMustBeReReadCorrectly() throws IOException {
     assumeWindows();
     assumeWslPresence();
     assumeTrue("'fsutil.exe' needs elevated privileges to work", SuperUserStatus.isSuperUser());
@@ -59,85 +60,78 @@ public class CaseSensitivityDetectionTest {
     assertEquals(CaseSensitivity.INSENSITIVE, FileSystemUtil.readParentCaseSensitivity(file));
   }
 
-  @Test
-  public void macOsBasics() {
+  @Test public void macOsBasics() {
     assumeMacOS();
 
-    File root = new File("/");
-    CaseSensitivity rootCs = FileSystemUtil.readParentCaseSensitivity(root);
+    var root = Path.of("/");
+    var rootCs = FileSystemUtil.readParentCaseSensitivity(root.toFile());
     assertNotEquals(CaseSensitivity.UNKNOWN, rootCs);
 
-    File child = new File("/Users");
-    assertEquals(root, child.getParentFile());
-    assertEquals(rootCs, FileSystemUtil.readParentCaseSensitivity(child));
+    var child = Path.of("/Users");
+    assertEquals(root, child.getParent());
+    assertEquals(rootCs, FileSystemUtil.readParentCaseSensitivity(child.toFile()));
   }
 
-  @Test
-  public void linuxBasics() {
+  @Test public void linuxBasics() {
     assumeLinux();
 
-    File root = new File("/");
-    CaseSensitivity rootCs = FileSystemUtil.readParentCaseSensitivity(root);
+    var root = Path.of("/");
+    var rootCs = FileSystemUtil.readParentCaseSensitivity(root.toFile());
     assertEquals(CaseSensitivity.SENSITIVE, rootCs);
 
-    File child = new File("/home");
-    assertEquals(rootCs, FileSystemUtil.readParentCaseSensitivity(child));
+    var child = Path.of("/home");
+    assertEquals(rootCs, FileSystemUtil.readParentCaseSensitivity(child.toFile()));
   }
 
-  @Test
-  public void caseSensitivityIsReadSanely() throws IOException {
-    File file = tempDir.newFile("dir/x.txt");
-    CaseSensitivity sensitivity = FileSystemUtil.readParentCaseSensitivity(file);
+  @Test public void caseSensitivityIsReadSanely() throws IOException {
+    var file = tempDir.newFileNio("dir/x.txt");
+    var sensitivity = FileSystemUtil.readParentCaseSensitivity(file.toFile());
     if (sensitivity == CaseSensitivity.SENSITIVE) {
-      assertTrue(new File(file.getParentFile(), "X.txt").createNewFile());
+      Files.createFile(file.resolveSibling("X.txt"));
     }
     else if (sensitivity == CaseSensitivity.INSENSITIVE) {
-      assertFalse(new File(file.getParentFile(), "X.txt").createNewFile());
+      assertThatCode(() -> Files.createFile(file.resolveSibling("X.txt")))
+        .doesNotThrowAnyExceptionExcept(FileAlreadyExistsException.class);
     }
     else {
       fail("invalid sensitivity: " + sensitivity);
     }
   }
 
-  @Test
-  public void caseSensitivityOfNonExistingDirMustBeUnknown() {
-    File file = new File(tempDir.getRoot(), "dir/child.txt");
-    assertFalse(file.exists());
-    assertEquals(CaseSensitivity.UNKNOWN, FileSystemUtil.readParentCaseSensitivity(file));
+  @Test public void caseSensitivityOfNonExistingDirMustBeUnknown() {
+    var file = tempDir.getRootPath().resolve("dir/child.txt");
+    assertFalse(Files.exists(file.getParent()));
+    assertEquals(CaseSensitivity.UNKNOWN, FileSystemUtil.readCaseSensitivityByNativeAPI(file.toFile()));
+    assertEquals(CaseSensitivity.UNKNOWN, FileSystemUtil.readCaseSensitivityByJavaIO(file.toFile()));
   }
 
-  @Test
-  public void nativeApiWorksInSimpleCases() {
-    File file = tempDir.newFile("dir/0");
-    assertFalse(FileSystemUtil.isCaseToggleable(file.getName()));
+  @Test public void nativeApiWorksInSimpleCases() {
+    var file = tempDir.newFileNio("dir/0");
+    assertFalse(FileSystemUtil.isCaseToggleable(file.getFileName().toString()));
 
-    CaseSensitivity expected = SystemInfo.isWindows || SystemInfo.isMac ? CaseSensitivity.INSENSITIVE : CaseSensitivity.SENSITIVE;
-    assertEquals(expected, FileSystemUtil.readParentCaseSensitivity(file));
+    var expected = OS.CURRENT == OS.Windows || OS.CURRENT == OS.macOS ? CaseSensitivity.INSENSITIVE : CaseSensitivity.SENSITIVE;
+    assertEquals(expected, FileSystemUtil.readParentCaseSensitivity(file.toFile()));
   }
 
-  @Test
-  public void nativeApiWorksWithNonLatinPaths() {
-    String uni = SystemInfo.isWindows ? getUnicodeName(System.getProperty("sun.jnu.encoding")) : getUnicodeName();
+  @Test public void nativeApiWorksWithNonLatinPaths() {
+    var uni = OS.CURRENT == OS.Windows ? getUnicodeName(System.getProperty("sun.jnu.encoding")) : getUnicodeName();
     assumeTrue(uni != null);
-    File file = tempDir.newFile(uni + "/0");
-    CaseSensitivity expected = SystemInfo.isWindows || SystemInfo.isMac ? CaseSensitivity.INSENSITIVE : CaseSensitivity.SENSITIVE;
-    assertEquals(expected, FileSystemUtil.readParentCaseSensitivity(file));
+    var file = tempDir.newFileNio(uni + "/0");
+    var expected = OS.CURRENT == OS.Windows || OS.CURRENT == OS.macOS ? CaseSensitivity.INSENSITIVE : CaseSensitivity.SENSITIVE;
+    assertEquals(expected, FileSystemUtil.readParentCaseSensitivity(file.toFile()));
   }
 
-  @Test
-  public void caseSensitivityNativeWrappersMustWorkAtLeastInSimpleCases() {
-    CaseSensitivity defaultCS = SystemInfo.isFileSystemCaseSensitive ? CaseSensitivity.SENSITIVE : CaseSensitivity.INSENSITIVE;
-    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByNativeAPI(tempDir.newFile("dir0/child.txt")));
-    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByNativeAPI(tempDir.newFile("dir0/0"))); // there's a toggleable "child.txt" in this dir already
-    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByNativeAPI(tempDir.newFile("dir1/0")));
+  @Test public void caseSensitivityNativeWrappersMustWorkAtLeastInSimpleCases() {
+    var defaultCS = SystemInfo.isFileSystemCaseSensitive ? CaseSensitivity.SENSITIVE : CaseSensitivity.INSENSITIVE;
+    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByNativeAPI(tempDir.newFileNio("dir0/child.txt").toFile()));
+    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByNativeAPI(tempDir.newFileNio("dir0/0").toFile())); // there's a toggleable "child.txt" in this dir already
+    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByNativeAPI(tempDir.newFileNio("dir1/0").toFile()));
   }
 
-  @Test
-  public void caseSensitivityMustBeDeducibleByPureJavaIOAtLeastInSimpleCases() {
-    CaseSensitivity defaultCS = SystemInfo.isFileSystemCaseSensitive ? CaseSensitivity.SENSITIVE : CaseSensitivity.INSENSITIVE;
-    assertEquals(defaultCS, FileSystemUtil.readParentCaseSensitivityByJavaIO(tempDir.newFile("dir0/child.txt")));
-    assertEquals(defaultCS, FileSystemUtil.readParentCaseSensitivityByJavaIO(tempDir.newFile("dir0/0"))); // there's a toggleable "child.txt" in this dir already
-    assertEquals(defaultCS, FileSystemUtil.readParentCaseSensitivityByJavaIO(tempDir.newDirectory("dir0/Ubuntu")));
-    //assertEquals(defaultCS, FileSystemUtil.readParentCaseSensitivityByJavaIO(tempDir.newFile("dir1/0")));
+  @Test public void caseSensitivityMustBeDeducibleByPureJavaIOAtLeastInSimpleCases() {
+    var defaultCS = SystemInfo.isFileSystemCaseSensitive ? CaseSensitivity.SENSITIVE : CaseSensitivity.INSENSITIVE;
+    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByJavaIO(tempDir.newFileNio("dir0/child.txt").toFile()));
+    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByJavaIO(tempDir.newFileNio("dir0/0").toFile())); // there's a toggleable "child.txt" in this dir already
+    assertEquals(defaultCS, FileSystemUtil.readCaseSensitivityByJavaIO(tempDir.newDirectoryPath("dir0/Ubuntu").toFile()));
   }
 }
diff --git a/platform/util/src/com/intellij/openapi/util/io/FileSystemUtil.java b/platform/util/src/com/intellij/openapi/util/io/FileSystemUtil.java
index e2ca5bf5a8dc..24098155c41a 100644
--- a/platform/util/src/com/intellij/openapi/util/io/FileSystemUtil.java
+++ b/platform/util/src/com/intellij/openapi/util/io/FileSystemUtil.java
@@ -3,7 +3,7 @@ package com.intellij.openapi.util.io;
 
 import com.intellij.jna.JnaLoader;
 import com.intellij.openapi.diagnostic.Logger;
-import com.intellij.openapi.util.SystemInfo;
+import com.intellij.util.system.OS;
 import com.sun.jna.*;
 import com.sun.jna.platform.win32.Kernel32;
 import com.sun.jna.platform.win32.WinBase;
@@ -44,7 +44,7 @@ public final class FileSystemUtil {
   }
 
   private static String normalizePath(@NotNull String path) {
-    if (SystemInfo.isWindows && path.length() == 2 && path.charAt(1) == ':') {
+    if (OS.CURRENT == OS.Windows && path.length() == 2 && path.charAt(1) == ':') {
       path += '\\';
     }
     return path;
@@ -141,12 +141,12 @@ public final class FileSystemUtil {
     FileAttributes.CaseSensitivity detected = readCaseSensitivityByNativeAPI(anyChild);
     if (detected.isKnown()) return detected;
     // native queries failed, fallback to the Java I/O:
-    return readParentCaseSensitivityByJavaIO(anyChild);
+    return readCaseSensitivityByJavaIO(anyChild);
   }
 
   @VisibleForTesting
   @ApiStatus.Internal
-  public static @NotNull FileAttributes.CaseSensitivity readParentCaseSensitivityByJavaIO(@NotNull java.io.File anyChild) {
+  public static @NotNull FileAttributes.CaseSensitivity readCaseSensitivityByJavaIO(@NotNull java.io.File anyChild) {
     // try to query this path by different-case strings and deduce case sensitivity from the answers
     java.io.File parent = anyChild.getParentFile();
     if (parent == null) {
@@ -238,21 +238,20 @@ public final class FileSystemUtil {
   @VisibleForTesting
   @ApiStatus.Internal
   public static @NotNull FileAttributes.CaseSensitivity readCaseSensitivityByNativeAPI(@NotNull java.io.File anyChild) {
-    FileAttributes.CaseSensitivity detected = com.intellij.openapi.util.io.FileAttributes.CaseSensitivity.UNKNOWN;
     if (JnaLoader.isLoaded()) {
       java.io.File parent = anyChild.getParentFile();
       String path = (parent != null ? parent : anyChild).getAbsolutePath();
-      if (SystemInfo.isWin10OrNewer && WINDOWS_CS_API_AVAILABLE) {
-        detected = OSAgnosticPathUtil.isAbsoluteDosPath(path) ? getNtfsCaseSensitivity(path) : com.intellij.openapi.util.io.FileAttributes.CaseSensitivity.UNKNOWN;
+      if (OS.CURRENT == OS.Windows && OS.CURRENT.isAtLeast(10, 0) && WINDOWS_CS_API_AVAILABLE && OSAgnosticPathUtil.isAbsoluteDosPath(path)) {
+        return getNtfsCaseSensitivity(path);
       }
-      else if (SystemInfo.isMac && MAC_CS_API_AVAILABLE) {
-        detected = getMacOsCaseSensitivity(path);
+      else if (OS.CURRENT == OS.macOS && MAC_CS_API_AVAILABLE) {
+        return getMacOsCaseSensitivity(path);
       }
-      else if (SystemInfo.isLinux && LINUX_CS_API_AVAILABLE) {
-        detected = getLinuxCaseSensitivity(path);
+      else if (OS.CURRENT == OS.Linux && LINUX_CS_API_AVAILABLE) {
+        return getLinuxCaseSensitivity(path);
       }
     }
-    return detected;
+    return FileAttributes.CaseSensitivity.UNKNOWN;
   }
 
   private static String toggleCase(String name) {