Prefer File.getCanonicalFile over Path.normalize

os/src/Path.scala

@@ -1,6 +1,7 @@
 package os
 
 import collection.JavaConverters._
+import util.Properties
 
 trait PathChunk{
   def segments: Seq[String]
@@ -384,7 +385,20 @@ object Path {
       throw PathError.AbsolutePathOutsideRoot
     }
 
-    val normalized = f.normalize()
+    fromNIO(f)
+  }
+
+  private def fromNIO(p: java.nio.file.Path): Path = {
+    // On Windows, File.getCanonicalFile normalizes 8.3 paths as long paths,
+    // whereas Path.normalize doesn't. So we use the former here.
+    val shouldUseIO = Properties.isWin &&
+      p.getFileSystem.getClass.getName == "sun.nio.fs.WindowsFileSystem"
+    val normalized =
+      if (shouldUseIO) {
+        require(p.isAbsolute, s"$p is not an absolute path")
+        p.toFile.getCanonicalFile.toPath
+      }
+      else p.normalize()
     new Path(normalized)
   }
 
@@ -437,8 +451,8 @@ class Path private[os](val wrapped: java.nio.file.Path)
 
   def /(chunk: PathChunk): ThisType = {
     if (chunk.ups > wrapped.getNameCount) throw PathError.AbsolutePathOutsideRoot
-    val resolved = wrapped.resolve(chunk.toString).normalize()
-    new Path(resolved)
+    val resolved = wrapped.resolve(chunk.toString)
+    Path.fromNIO(resolved)
   }
   override def toString = wrapped.toString
 

os/test/src/PathTests.scala

@@ -4,6 +4,7 @@ import java.nio.file.Paths
 
 import os._
 import utest.{assert => _, _}
+import scala.util.Properties
 object PathTests extends TestSuite{
   val tests = Tests {
     test("Basic"){
@@ -381,5 +382,21 @@ object PathTests extends TestSuite{
         }
       }
     }
+    test("Windows short paths"){
+      if (Properties.isWin) {
+        val dir = os.temp.dir(prefix = "os-lib-tests")
+
+        val file = dir / "long-dir-name" / "long-file-name.txt"
+        // uncomment this line to make the test fail :/
+        // val shortBefore = dir / "LONG-D~1" / "LONG-F~1.txt"
+
+        val content = "os-lib test"
+        os.write(file, content, createFolders = true)
+
+        val short = dir / "LONG-D~1" / "LONG-F~1.txt"
+        assert(os.read(short) == content)
+        assert(file == short)
+      }
+    }
   }
 }