`geom_vline()` and friends cannot use `mapping` when `xintercept` is set

I wanted to make geom_vline() adopt the theme's accent colour. Below was my sequence of attempts:

library(ggplot2)

ggplot() + geom_vline(xintercept = 0, colour = from_theme(accent))
#> Error:
#> ! object 'accent' not found
ggplot() + geom_vline(aes(colour = from_theme(accent)), xintercept = 0)
#> Warning: `geom_vline()`: Ignoring `mapping` because `xintercept` was provided.

ggplot() + geom_vline(aes(xintercept = 0, colour = from_theme(accent)))

^{Created on 2026-04-03 with reprex v2.1.1}

The first is obviously wrong because from_theme() only works inside aes(). The second seems like it should work, but the geoms are being too strict.

In the past I understand why it might have been discouraged to use mapping, but I think with the newer features like from_theme() the situation changed a bit and the limitation seems unnecessary.

Would it be worth making geom_vline(aes(colour = from_theme(accent)), xintercept = 0) work?

Start at the geom_vline() implementation and trace how it handles mapping when xintercept is supplied, including the related geoms mentioned in the issue. Confirm the behavior with the provided from_theme(accent) example; done means mapping is accepted alongside xintercept without the warning and the line uses the theme accent colour.