geom_raster() fallback for non-linear Cartesian coordinates

[teunbrand]

This PR aims to fix #6382 and amends #5627.

It kicks off the fallback mechanism too if the coord is non-linear. I hadn't foreseen at the time that coord_sf() is technically a non-linear child-coordinate of coord_cartesian().

Reprex from the issue:

devtools::load_all("~/packages/ggplot2")
#> ℹ Loading ggplot2
library(sf)
#> Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.3.1; sf_use_s2() is TRUE

file <- file.choose()
data <- read.csv(file, row.names = 1)

targetcrs <- paste(
  "+proj=lcc", 
  "+lat_1=25", 
  "+lat_2=47", 
  "+lon_0=105", 
  "+datum=WGS84", 
  "+units=m", 
  sep = " "
)

ggplot(data = data, aes(x = x, y = y))+
  geom_raster(aes(fill = value))+
  facet_wrap(~class)+
  coord_sf(
    crs = st_crs('epsg:32649'),
    default_crs = st_crs('epsg:4326')
  )
#> `geom_raster()` only works with `coord_cartesian()`.
#> ℹ Falling back to drawing as `geom_rect()`.
#> `geom_raster()` only works with `coord_cartesian()`.
#> ℹ Falling back to drawing as `geom_rect()`.
#> `geom_raster()` only works with `coord_cartesian()`.
#> ℹ Falling back to drawing as `geom_rect()`.

^{Created on 2025-03-27 with reprex v2.1.1}

[thomasp85]

Shouldn't it be enough to test coord$is_linear() and forget about the special case for CoordCartesian?

The message below also needs an update

[teunbrand]

Yeah good points, I agree

[thomasp85]

LGTM

[Breeze-Hu]

Great!
Thanks : )