Fix symlink creation on older Windows versions

src/main/native/windows/BUILD

@@ -25,6 +25,9 @@ cc_library(
         "file.h",
         "util.h",
     ],
+    linkopts = [
+        "-DEFAULTLIB:advapi32.lib", # RegGetValueW
+    ],
     visibility = [
         "//src/main/cpp:__subpackages__",
         "//src/main/tools:__pkg__",

src/main/native/windows/file.cc

@@ -39,6 +39,20 @@ namespace windows {
 using std::unique_ptr;
 using std::wstring;
 
+bool IsDeveloperModeEnabled() {
+  DWORD val = 0;
+  DWORD valSize = sizeof(val);
+  if (RegGetValueW(
+          HKEY_LOCAL_MACHINE,
+          L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\AppModelUnlock",
+          L"AllowDevelopmentWithoutDevLicense", RRF_RT_DWORD, nullptr, &val,
+          &valSize) != ERROR_SUCCESS) {
+    return false;
+  }
+  return val != 0;
+}
+
+
 wstring AddUncPrefixMaybe(const wstring& path) {
   return path.empty() || IsDevNull(path.c_str()) || HasUncPrefix(path.c_str())
              ? path
@@ -446,13 +460,14 @@ int CreateSymlink(const wstring& symlink_name, const wstring& symlink_target,
   }
 
   if (!CreateSymbolicLinkW(name.c_str(), target.c_str(),
-                           SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE)) {
-     // The flag SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE requires
-     // developer mode enabled, which we expect if using symbolic linking.
-     *error = MakeErrorMessage(
-               WSTR(__FILE__), __LINE__, L"CreateSymlink", symlink_target,
-               L"createSymbolicLinkW failed");
-     return CreateSymlinkResult::kError;
+                           symlinkPrivilegeFlag)) {
+    *error = MakeErrorMessage(
+              WSTR(__FILE__), __LINE__, L"CreateSymlink", symlink_target,
+              GetLastError() == ERROR_PRIVILEGE_NOT_HELD
+               ? L"createSymbolicLinkW failed (permission denied). Either "
+                 "Windows developer mode or admin privileges are required."
+               : L"createSymbolicLinkW failed");
+    return CreateSymlinkResult::kError;
   }
   return CreateSymlinkResult::kSuccess;
 }

src/main/native/windows/file.h

@@ -18,12 +18,12 @@
 #define WIN32_LEAN_AND_MEAN
 #endif
 
+#include <windows.h>
+
 #ifndef SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
 #define SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE 0x2
 #endif
 
-#include <windows.h>
-
 #include <memory>
 #include <string>
 
@@ -33,6 +33,16 @@ namespace windows {
 using std::unique_ptr;
 using std::wstring;
 
+bool IsDeveloperModeEnabled();
+
+// The flag SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE requires
+// developer mode to be enabled. If it is not enabled, or the current
+// version of Windows does not support it, do not use the flag.
+// The process will need to be run with elevated privileges.
+const DWORD symlinkPrivilegeFlag = IsDeveloperModeEnabled()
+    ? SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
+    : 0;
+
 template <typename char_type>
 bool HasUncPrefix(const char_type* path) {
   // Return true iff `path` starts with "\\?\", "\\.\", or "\??\".

src/main/tools/BUILD

@@ -60,12 +60,6 @@ cc_binary(
         "//src/conditions:windows": ["build-runfiles-windows.cc"],
         "//conditions:default": ["build-runfiles.cc"],
     }),
-    linkopts = select({
-        "//src/conditions:windows": [
-            "-DEFAULTLIB:advapi32.lib",  # RegGetValueW
-        ],
-        "//conditions:default": [],
-    }),
     deps = ["//src/main/cpp/util:filesystem"] + select({
         "//src/conditions:windows": ["//src/main/native/windows:lib-file"],
         "//conditions:default": [],

src/main/tools/build-runfiles-windows.cc

@@ -129,19 +129,6 @@ bool ReadSymlink(const wstring& abs_path, wstring* target, wstring* error) {
   return false;
 }
 
-bool IsDeveloperModeEnabled() {
-  DWORD val = 0;
-  DWORD valSize = sizeof(val);
-  if (RegGetValueW(
-          HKEY_LOCAL_MACHINE,
-          L"SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\AppModelUnlock",
-          L"AllowDevelopmentWithoutDevLicense", RRF_RT_DWORD, nullptr, &val,
-          &valSize) != ERROR_SUCCESS) {
-    return false;
-  }
-  return val != 0;
-}
-
 }  // namespace
 
 class RunfilesCreator {
@@ -211,10 +198,8 @@ class RunfilesCreator {
   }
 
   void CreateRunfiles() {
-    bool symlink_needs_privilege =
-        DoesCreatingSymlinkNeedAdminPrivilege(runfiles_output_base_);
     ScanTreeAndPrune(runfiles_output_base_);
-    CreateFiles(symlink_needs_privilege);
+    CreateFiles();
     CopyManifestFile();
   }
 
@@ -247,48 +232,6 @@ class RunfilesCreator {
     }
   }
 
-  bool DoesCreatingSymlinkNeedAdminPrivilege(const wstring& runfiles_base_dir) {
-    // Creating symlinks without admin privilege is enabled by Developer Mode,
-    // available since Windows Version 1703.
-    if (IsDeveloperModeEnabled()) {
-      return false;
-    }
-    wstring dummy_link = runfiles_base_dir + L"\\dummy_link";
-    wstring dummy_target = runfiles_base_dir + L"\\dummy_target";
-
-    // Try creating symlink with admin privilege
-    bool created =
-        CreateSymbolicLinkW(dummy_link.c_str(), dummy_target.c_str(), 0);
-
-    // on a rare occasion the dummy_link may exist from a previous run
-    // retry after deleting the existing link
-    if (!created && GetLastError() == ERROR_ALREADY_EXISTS) {
-      DeleteFileOrDie(dummy_link);
-      created =
-          CreateSymbolicLinkW(dummy_link.c_str(), dummy_target.c_str(), 0);
-    }
-
-    // If we couldn't create symlink, print out an error message and exit.
-    if (!created) {
-      if (GetLastError() == ERROR_PRIVILEGE_NOT_HELD) {
-        die(L"CreateSymbolicLinkW failed:\n%hs\n",
-            "Bazel needs to create symlink for building runfiles tree.\n"
-            "Creating symlink on Windows requires either of the following:\n"
-            "    1. Program is running with elevated privileges (Admin "
-            "rights).\n"
-            "    2. The system version is Windows 10 Creators Update (1703) or "
-            "later and "
-            "developer mode is enabled.",
-            GetLastErrorString().c_str());
-      } else {
-        die(L"CreateSymbolicLinkW failed: %hs", GetLastErrorString().c_str());
-      }
-    }
-
-    DeleteFileOrDie(dummy_link);
-    return true;
-  }
-
   // This function scan the current directory, remove all
   // files/symlinks/directories that are not presented in manifest file. If a
   // symlink already exists and points to the correct target, this function
@@ -360,11 +303,7 @@ class RunfilesCreator {
     ::FindClose(handle);
   }
 
-  void CreateFiles(bool creating_symlink_needs_admin_privilege) {
-    DWORD privilege_flag = creating_symlink_needs_admin_privilege
-                               ? 0
-                               : SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
-
+  void CreateFiles() {
     for (const auto& it : manifest_file_map) {
       // Ensure the parent directory exists
       wstring parent_dir = GetParentDirFromPath(it.first);
@@ -395,9 +334,20 @@ class RunfilesCreator {
           create_dir = SYMBOLIC_LINK_FLAG_DIRECTORY;
         }
         if (!CreateSymbolicLinkW(it.first.c_str(), it.second.c_str(),
-                                 privilege_flag | create_dir)) {
-          die(L"CreateSymbolicLinkW failed (%s -> %s): %hs", it.first.c_str(),
-              it.second.c_str(), GetLastErrorString().c_str());
+                                 bazel::windows::symlinkPrivilegeFlag | create_dir)) {
+
+          if (GetLastError() == ERROR_PRIVILEGE_NOT_HELD) {
+            die(L"CreateSymbolicLinkW failed:\n%hs\n",
+                "Bazel needs to create symlinks to build the runfiles tree.\n"
+                "Creating symlinks on Windows requires one of the following:\n"
+                "    1. Bazel is run with administrator privileges.\n"
+                "    2. The system version is Windows 10 Creators Update (1703) or "
+                "later and developer mode is enabled.",
+                GetLastErrorString().c_str());
+          } else {
+              die(L"CreateSymbolicLinkW failed (%s -> %s): %hs", it.first.c_str(),
+                  it.second.c_str(), GetLastErrorString().c_str());
+          }
         }
       }
     }