[josefelipe0036]

Fixes #6360.

Root cause

For free space, Facet$init_gtable() sizes each panel with diff(ranges[[i]]$x.range) (or y.range). The panel parameters of coord_radial() and coord_polar() use theta.range/r.range instead, and coord_sf() uses x_range/y_range, so diff(NULL) returns numeric(0) and vapply() fails with an error that mentions neither the facet nor the coord:

Error in vapply(idx, function(i) diff(ranges[[i]]$x.range), numeric(1)):
  values must be length 1, but FUN(X[[1]]) result is length 0

facet_wrap() and facet_grid() share Facet$draw_panels(), so both fail, for space = "free_x", "free_y" and "free", and the problem isn't limited to coord_radial(): coord_polar() and coord_sf() fail the same way.

Fix

Facet$draw_panels() now checks that the panel parameters have a position range in the free direction. If they don't, it warns and falls back to fixed space:

`facet_wrap()` can't use free `space` with `coord_radial()`.

As discussed in the issue, this no longer throws an error, and it doesn't try to give space a meaning in polar coordinates, where the panel aspect ratio follows the bounding box of the arc rather than the data range. Coords that have x.range/y.range (coord_cartesian(), coord_transform(), coord_flip(), coord_map(), ...) are unaffected: only combinations that used to error behave differently.

Reprex

library(ggplot2)
ggplot(mtcars, aes(disp, mpg)) +
  geom_point() +
  facet_wrap(
    vars(cyl),
    nrow = 1L, scales = "free_x", space = "free_x",
    strip.position = "top"
  ) +
  coord_radial(start = -0.4 * pi, end = 0.4 * pi, inner.radius = 0.3)

facet + coord	before (main @ b638d65)	after
the plot above (facet_wrap(space = "free_x") + coord_radial())	error	renders, warns
facet_wrap(space = "free_y") + coord_radial()	error	renders, warns
facet_grid(space = "free_x") + coord_radial()	error	renders, warns
facet_grid(scales = "free", space = "free") + coord_radial()	error	renders, warns
facet_grid(space = "free_x") + coord_polar()	error	renders, warns
facet_grid(space = "free_x") + coord_sf()	error	renders, warns
facet_grid(scales = "free_x", space = "free_x") + Cartesian, coord_transform(), coord_flip()	renders	renders, no warning (unchanged)

Tests

New test in test-facet-.R:

• a visual test of the plot from the issue (expect_doppelganger() inside expect_snapshot_warning(), following the pattern in test-geom-path.R);
• the panel sizes with free space equal those with space = "fixed" for facet_wrap() + coord_radial(), facet_grid() + coord_polar(), facet_grid() + coord_sf(), and a facet factor with an unused level and an NA (drop = FALSE, so one panel is empty) + coord_radial().

The test fails on main with the error above and passes with this change.

Run locally on R 4.6.0 (Windows 11):

• devtools::test(): 2988 expectations, 0 failures, 0 errors, 0 warnings, 0 skips.
• devtools::check(document = TRUE, args = "--no-manual"): 0 errors | 0 warnings | 1 note. The note (checking Rd metadata: Rd files without \alias: 'shared_layer_parameters.Rd') comes from man/shared_layer_parameters.Rd, which this PR doesn't touch, so it is also present on main.

Note: help with this issue was offered in March 2025, but there has been no activity on it since. Happy to step back if someone is already working on it.

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