cmake: Add '-E create_symlink' support on Windows

The allows `-E create_symlink` to work on Windows.  It utilizes
`uv_fs_symlink`.  I am still unsure exactly which Windows platforms will
work without requiring Administrator privileges or needing a user/group
with the "Create Symbolic Links" User Rights.  It does work with my
Windows 10 Pro with Developer Mode turned on.  In the test suite check
that the symlink either worked or failed with a permissions error.

Use recent changes in cmSystemTools::FileExists to check that a symlink
is broken.

1 files changed, 23 insertions, 2 deletions

diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index 79e5ccf..8339aac 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -6,6 +6,7 @@
 #include "cmDuration.h"
 #include "cmProcessOutput.h"
 #include "cm_sys_stat.h"
+#include "cm_uv.h"
 
 #if defined(CMAKE_BUILD_WITH_CMAKE)
 #  include "cmArchiveWrite.h"
@@ -55,8 +56,6 @@
 #  include <wincrypt.h>
 
 #  include <fcntl.h> /* _O_TEXT */
-
-#  include "cm_uv.h"
 #else
 #  include <sys/time.h>
 #  include <unistd.h>
@@ -2988,3 +2987,25 @@ bool cmSystemTools::StringToULong(const char* str, unsigned long* value)
   *value = strtoul(str, &endp, 10);
   return (*endp == '\0') && (endp != str) && (errno == 0);
 }
+
+bool cmSystemTools::CreateSymlink(const std::string& origName,
+                                  const std::string& newName)
+{
+  uv_fs_t req;
+  int flags = 0;
+#if defined(_WIN32)
+  if (cmsys::SystemTools::FileIsDirectory(origName)) {
+    flags |= UV_FS_SYMLINK_DIR;
+  }
+#endif
+  int err = uv_fs_symlink(nullptr, &req, origName.c_str(), newName.c_str(),
+                          flags, nullptr);
+  if (err) {
+    std::string e =
+      "failed to create symbolic link '" + newName + "': " + uv_strerror(err);
+    cmSystemTools::Error(e.c_str());
+    return false;
+  }
+
+  return true;
+}