Windows: Path.readSymbolicLink fails for junctions

[laszlocsomor]

Description of the problem / feature request:

Path.readSymbolicLink calls FileSystem.readSymbolicLink:

bazel/src/main/java/com/google/devtools/build/lib/vfs/Path.java

Line 599 in d7aa53e

return fileSystem.readSymbolicLink(this);

On Windows, this calls into JavaIoFileSystem, which calls java.nio.file.Files.readSymbolicLink, which is unaware of junctions.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

The bug is rooted in java.nio, so here's an out-of-bazel repro:

BUILD:

java_binary(
    name = "x",
    srcs = ["ReadJunc.java"],
    main_class = "ReadJunc",
)

ReadJunc.java:

import java.nio.file.Files;
import java.nio.file.FileSystems;
import java.nio.file.Path;

public class ReadJunc {
  public static void main(String[] args) throws Exception {
    System.err.println("Hello ReadJunc");

    Path path = FileSystems.getDefault().getPath("c:\\src\\bazel-releases\\current");
    System.err.printf("path=(%s) isdir=%d%n",
        path, path.toFile().isDirectory() ? 1 : 0);

    Path path2 = Files.readSymbolicLink(path);
    System.err.printf("path2=(%s)%n", path2);
  }
}

output:

C:\src\tmp>bazel run x
...
path=(c:\src\bazel-releases\current) isdir=1
Exception in thread "main" java.nio.file.NotLinkException: Reparse point is not a symbolic link
        at sun.nio.fs.WindowsLinkSupport.readLinkImpl(WindowsLinkSupport.java:318)
        at sun.nio.fs.WindowsLinkSupport.readLink(WindowsLinkSupport.java:59)
        at sun.nio.fs.WindowsFileSystemProvider.readSymbolicLink(WindowsFileSystemProvider.java:628)
        at java.nio.file.Files.readSymbolicLink(Files.java:1432)
        at ReadJunc.main(ReadJunc.java:13)

The particular path:

C:\src\tmp>dir c:\src\bazel-releases
...
2019-03-27  11:12    <JUNCTION>     current [C:\src\bazel-releases\0.24.0]

What operating system are you running Bazel on?

Windows 10