Better respect theme settings when drawing coord_sf() panel grid (#3113)

* Make coord_sf() panel grid mimic coord_cartesian() panel grid. Closes #2991. Closes #2525.

* don't drop gray background

* add unit test

* don't error if line size is undefined

Author: clauswilke

NEWS.md

@@ -1,5 +1,10 @@
 # ggplot2 3.1.0.9000
 
+* `coord_sf()` graticule lines are now drawn in the same thickness as 
+  panel grid lines in `coord_cartesian()`, and seting panel grid
+  lines to `element_blank()` now also works in `coord_sf()` 
+  (@clauswilke, #2991, #2525).
+
 * `geom_hline()`, `geom_vline()`, and `geom_abline()` now throw a warning if the user supplies both an `xintercept`, `yintercept`, or `slope` value and a mapping (@RichardJActon, #2950).
 
 * `scale_color_continuous()` now points at `scale_colour_continuos()` so that it 

R/coord-sf.R

@@ -195,11 +195,22 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
 
   render_bg = function(self, panel_params, theme) {
     el <- calc_element("panel.grid.major", theme)
-    line_gp <- gpar(col = el$colour, lwd = el$size, lty = el$linetype)
-    grobs <- c(
-      list(element_render(theme, "panel.background")),
-      lapply(sf::st_geometry(panel_params$graticule), sf::st_as_grob, gp = line_gp)
-    )
+
+    # we don't draw the graticules if the major panel grid is
+    # turned off
+    if (inherits(el, "element_blank")) {
+      grobs <- list(element_render(theme, "panel.background"))
+    } else {
+      line_gp <- gpar(
+        col = el$colour,
+        lwd = len0_null(el$size*.pt),
+        lty = el$linetype
+      )
+      grobs <- c(
+        list(element_render(theme, "panel.background")),
+        lapply(sf::st_geometry(panel_params$graticule), sf::st_as_grob, gp = line_gp)
+      )
+    }
     ggname("grill", do.call("grobTree", grobs))
   },
 

tests/figs/coord-sf/no-panel-grid.svg

@@ -1,6 +1,6 @@
 context("coord_sf")
 
-test_that("multiplication works", {
+test_that("basic plot builds without error", {
   skip_if_not_installed("sf")
 
   nc <- sf::st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)
@@ -15,6 +15,18 @@ test_that("multiplication works", {
   expect_doppelganger("sf-polygons", plot)
 })
 
+test_that("graticule lines can be removed via theme", {
+  skip_if_not_installed("sf")
+
+  df <- data_frame(x = c(1, 2, 3), y = c(1, 2, 3))
+  plot <- ggplot(df, aes(x, y)) +
+    geom_point() +
+    coord_sf() +
+    theme_gray() + # to test for presence of background grob
+    theme(panel.grid = element_blank())
+
+  expect_doppelganger("no panel grid", plot)
+})
 
 test_that("axis labels can be set manually", {
   skip_if_not_installed("sf")