Remove target path's forward slashes in File.symlink on Windows (#1…

…4522)

spec/std/file_spec.cr

@@ -418,6 +418,15 @@ describe "File" do
         File.same?(in_path, out_path, follow_symlinks: true).should be_true
       end
     end
+
+    it "works if destination contains forward slashes (#14520)" do
+      with_tempfile("test_slash_dest.txt", "test_slash_link.txt") do |dest_path, link_path|
+        File.write(dest_path, "hello")
+        File.symlink("./test_slash_dest.txt", link_path)
+        File.same?(dest_path, link_path, follow_symlinks: true).should be_true
+        File.read(link_path).should eq("hello")
+      end
+    end
   end
 
   describe "symlink?" do

src/crystal/system/win32/file.cr

@@ -319,7 +319,7 @@ module Crystal::System::File
   end
 
   def self.symlink(old_path : String, new_path : String) : Nil
-    win_old_path = System.to_wstr(old_path)
+    win_old_path = System.to_wstr(old_path.gsub('/', '\\'))
     win_new_path = System.to_wstr(new_path)
     info = info?(old_path, true)
     flags = info.try(&.type.directory?) ? LibC::SYMBOLIC_LINK_FLAG_DIRECTORY : 0