ggdesplot(): position num/text labels correctly when the formula has no fill variable

[SchmidtPaul]

Problem

Following up on your note that ggdesplot(oats35, ~ col+row|block, num=gen) did not look right: with an empty formula left-hand side (no fill variable) ggdesplot() adds no geom_tile, so nothing establishes the ±0.5 cell extent. The num/text labels on the outer cells then sit exactly on the panel border and get clipped, whereas the lattice desplot() reserves that extent regardless of fill.

Reproducer (against the current main)

library(desplot)
oats35 <- agridat::yates.oats
ggdesplot(oats35, ~ col+row|block, num=gen)  # labels clipped at the panel edges
desplot(oats35,   ~ col+row|block, num=gen)  # lattice centres them

The gg panels' x-range collapses to the outer column centres (e.g. [3, 4] for a two-column block), so a label at either column lands on the border.

Fix

Draw an invisible (fill = "transparent") tile grid in the no-fill case, mirroring what the lattice path already does. The extent then reaches half a cell beyond the outer centres and the labels are centred. Guarded by fill.type == "none", so filled plots are untouched. Added a regression test that checks the panel x-range covers the full cell extent and that a tile layer is present.

This branch also folds in a small follow-up to your suppressWarnings() cleanup: the one remaining suppressWarnings() (the deliberate col.regions positional-fallback warning) is now asserted with expect_warning(..., "positional") instead of being hidden.

Related to your comment on the ggdesplot(oats35, ~ col+row|block, num=gen) line in test_desplot.R.

Prepared with the help of an AI coding assistant; the reproducer above was run and verified locally.

[kwstat]

Excellent. Thanks.