Don't attach external packages

NEWS.md

@@ -5,6 +5,11 @@
   lines to `element_blank()` now also works in `coord_sf()` 
   (@clauswilke, #2991, #2525).
 
+* ggplot2 no longer attaches any external packages when using functions that depend on
+  packages that are suggested but not imported by ggplot2. The affected functions
+  include `geom_hex()`, `stat_binhex()`, `stat_summary_hex()`, `geom_quantile()`,
+  `stat_quantile()`, and `map_data()` (@clauswilke, #3126).
+
 * `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/stat-quantile.r

@@ -1,7 +1,7 @@
 #' @param quantiles conditional quantiles of y to calculate and display
 #' @param formula formula relating y variables to x variables
-#' @param method Quantile regression method to use.  Currently only supports
-#'    [quantreg::rq()].
+#' @param method Quantile regression method to use. Available options are `"rq"` (for
+#'    [`quantreg::rq()`]) and `"rqss"` (for [`quantreg::rqss()`]).
 #' @inheritParams layer
 #' @inheritParams geom_point
 #' @section Computed variables:
@@ -54,9 +54,13 @@ StatQuantile <- ggproto("StatQuantile", Stat,
 
     if (is.null(formula)) {
       if (method == "rqss") {
-        try_require("MatrixModels", "stat_quantile")
-        formula <- eval(substitute(y ~ qss(x, lambda = lambda)),
-          list(lambda = lambda))
+        formula <- eval(
+          substitute(y ~ qss(x, lambda = lambda)),
+          list(lambda = lambda)
+        )
+        # make qss function available in case it is needed;
+        # works around limitation in quantreg
+        qss <- quantreg::qss
       } else {
         formula <- y ~ x
       }
@@ -73,7 +77,15 @@ StatQuantile <- ggproto("StatQuantile", Stat,
     }
     grid <- new_data_frame(list(x = xseq))
 
-    method <- match.fun(method)
+    # if method was specified as a character string, replace with
+    # the corresponding function
+    if (identical(method, "rq")) {
+      method <- quantreg::rq
+    } else if (identical(method, "rqss")) {
+      method <- quantreg::rqss
+    } else {
+      method <- match.fun(method) # allow users to supply their own methods
+    }
 
     rbind_dfs(lapply(quantiles, quant_pred, data = data, method = method,
       formula = formula, weight = weight, grid = grid, method.args = method.args))

R/utilities.r

@@ -42,9 +42,13 @@ clist <- function(l) {
   paste(paste(names(l), l, sep = " = ", collapse = ", "), sep = "")
 }
 
+
+# Test whether package `package` is available. `fun` provides
+# the name of the ggplot2 function that uses this package, and is
+# used only to produce a meaningful error message if the
+# package is not available.
 try_require <- function(package, fun) {
   if (requireNamespace(package, quietly = TRUE)) {
-    library(package, character.only = TRUE)
     return(invisible())
   }