Handle when geometry is not a symbol (#4127)

Fix #4122

* Handle when `geometry` is not a symbol

* Fix a comment

Author: yutannihilation

R/layer-sf.R

@@ -52,7 +52,7 @@ LayerSf <- ggproto("LayerSf", Layer,
       self$geom_params$legend <- "polygon"
 
       # now check if the type should not be polygon
-      if (!is.null(self$mapping$geometry)) {
+      if (!is.null(self$mapping$geometry) && quo_is_symbol(self$mapping$geometry)) {
         geometry_column <- as_name(self$mapping$geometry)
         if (inherits(data[[geometry_column]], "sfc")) {
           sf_type <- detect_sf_type(data[[geometry_column]])

tests/testthat/test-geom-sf.R

@@ -76,6 +76,13 @@ test_that("geom_sf() determines the legend type from mapped geometry column", {
     ggplot(d_sf) + geom_sf(aes(geometry = g_line, colour = "a"))
   )
   expect_identical(p$plot$layers[[1]]$geom_params$legend, "line")
+
+  # If `geometry` is not a symbol, `LayerSf$setup_layer()` gives up guessing
+  # the legend type, and falls back to "polygon"
+  p <- ggplot_build(
+    ggplot(d_sf) + geom_sf(aes(geometry = identity(g_point), colour = "a"))
+  )
+  expect_identical(p$plot$layers[[1]]$geom_params$legend, "polygon")
 })
 
 test_that("geom_sf() removes rows containing missing aes", {