Lazy variables of css custom properties with less functions (even if it's overwritten) will break building

To simplify the issue, let's assume a third-party-library which contains:

// `library/style.less`
@base-color: green;
@dark-color: darken(@base-color, 50%);

.some-class {
  color: @base-color;
  backgroundColor: @dark-color;
}

And my app would like to override the colors to css custom properties:

// app.less
import "~library/style.less";

@base-color: var(--primary-color);
@dark-color: var(--bg-color);

:root {
  --primary-color: #fff;
  --bg-color: #000;
}

html[data-theme="dark"] {
  --primary-color: #000;
  --bg-color: #fff;
}

In which I want to override both the @base-color and @dark-color less variables. However, the less will fail with LessError: error evaluating function `darken`: Argument cannot be evaluated to a color, even if the @dark-color in library is actually overridden in my app, and no darken() function should be called.