Windows,JNI: more robust nativeCreateJunction

Rewrite the CreateJunction function in the Windows
JNI library.

The new implementation's improvements:

- succeeds if the junction already exists with the
  desired target; hopefully this will fix issue
  https://github.com/bazelbuild/bazel/issues/5433

- tolerant to concurrent filesystem modifications,
  e.g. if the junction's path suddenly disappears,
  the function reports the error correctly

Fixes https://github.com/bazelbuild/bazel/issues/5433

Change-Id: I58a2314a00f6edaa7c36c35ba54616168b44eb7d

Closes #5528.

Change-Id: I9f5dc9237b70a433d0d8c2578a826de3d462d110
PiperOrigin-RevId: 203744515

1 files changed, 3 insertions, 2 deletions

diff --git a/src/tools/launcher/java_launcher.cc b/src/tools/launcher/java_launcher.cc
index 82eeb0bcab..9e79627fa7 100644
--- a/src/tools/launcher/java_launcher.cc
+++ b/src/tools/launcher/java_launcher.cc
@@ -226,8 +226,9 @@ wstring JavaBinaryLauncher::CreateClasspathJar(const wstring& classpath) {
           junction = junction_base_dir_norm + L"\\" +
                      std::to_wstring(junction_count++);
 
-          wstring error(bazel::windows::CreateJunction(junction, jar_dir));
-          if (!error.empty()) {
+          wstring error;
+          if (bazel::windows::CreateJunction(junction, jar_dir, &error) !=
+              bazel::windows::CreateJunctionResult::kSuccess) {
             die(L"CreateClasspathJar failed: %s", error.c_str());
           }