Fix File.exists? for special devices on Windows

spec/std/file_spec.cr

@@ -234,6 +234,10 @@ describe "File" do
         File.exists?(bad_path).should be_false
       end
     end
+
+    it "gives true for null file (#15019)" do
+      File.exists?(File::NULL).should be_true
+    end
   end
 
   describe "file?" do

src/crystal/system/win32/file.cr

@@ -200,10 +200,32 @@ module Crystal::System::File
 
   private def self.accessible?(path, *, check_writable, follow_symlinks)
     if follow_symlinks
-      path = realpath?(path) || return false
+      path = realpath?(path, check_exists: false) || return false
+    end
+
+    handle = LibC.CreateFileW(
+      System.to_wstr(path),
+      LibC::FILE_READ_ATTRIBUTES,
+      LibC::DEFAULT_SHARE_MODE,
+      nil,
+      LibC::OPEN_EXISTING,
+      LibC::FILE_FLAG_BACKUP_SEMANTICS | LibC::FILE_FLAG_OPEN_REPARSE_POINT,
+      LibC::HANDLE.null,
+    )
+    return false if handle == LibC::INVALID_HANDLE_VALUE
+
+    begin
+      info = uninitialized LibC::FILE_ATTRIBUTE_TAG_INFO
+      if LibC.GetFileInformationByHandleEx(handle, LibC::FILE_INFO_BY_HANDLE_CLASS::FileAttributeTagInfo, pointerof(info), sizeof(typeof(info))) == 0
+        # this can happen to special files like NUL and COM1, but we managed to
+        # open them anyway, so assume they are readable and writable
+        return true
+      end
+      attributes = info.fileAttributes
+    ensure
+      LibC.CloseHandle(handle)
     end
 
-    attributes = LibC.GetFileAttributesW(System.to_wstr(path))
     return false if attributes == LibC::INVALID_FILE_ATTRIBUTES
     return true if attributes.bits_set?(LibC::FILE_ATTRIBUTE_DIRECTORY)
     return false if check_writable && attributes.bits_set?(LibC::FILE_ATTRIBUTE_READONLY)
@@ -298,7 +320,7 @@ module Crystal::System::File
 
   private REALPATH_SYMLINK_LIMIT = 100
 
-  private def self.realpath?(path : String) : String?
+  private def self.realpath?(path : String, *, check_exists : Bool = true) : String?
     REALPATH_SYMLINK_LIMIT.times do
       win_path = System.to_wstr(path)
 
@@ -319,7 +341,7 @@ module Crystal::System::File
         next
       end
 
-      return exists?(realpath, follow_symlinks: false) ? realpath : nil
+      return !check_exists || exists?(realpath, follow_symlinks: false) ? realpath : nil
     end
 
     raise ::File::Error.from_os_error("Too many symbolic links", Errno::ELOOP, file: path)

src/lib_c/x86_64-windows-msvc/c/minwinbase.cr

@@ -46,7 +46,8 @@ lib LibC
   end
 
   enum FILE_INFO_BY_HANDLE_CLASS
-    FileBasicInfo = 0
+    FileBasicInfo        = 0
+    FileAttributeTagInfo = 9
   end
 
   LOCKFILE_FAIL_IMMEDIATELY = DWORD.new(0x00000001)

src/lib_c/x86_64-windows-msvc/c/winbase.cr

@@ -72,6 +72,11 @@ lib LibC
     fileAttributes : DWORD
   end
 
+  struct FILE_ATTRIBUTE_TAG_INFO
+    fileAttributes : DWORD
+    reparseTag : DWORD
+  end
+
   fun GetFileInformationByHandleEx(hFile : HANDLE, fileInformationClass : FILE_INFO_BY_HANDLE_CLASS, lpFileInformation : Void*, dwBufferSize : DWORD) : BOOL
 
   fun LookupAccountNameW(lpSystemName : LPWSTR, lpAccountName : LPWSTR, sid : SID*, cbSid : DWORD*, referencedDomainName : LPWSTR, cchReferencedDomainName : DWORD*, peUse : SID_NAME_USE*) : BOOL