Use find.package() in library/require shim

Ensures that errors encountered during require() are displayed to
the end user rather than hidden during package existence testing.

Also, early return if package not installed during hook.

packages/webr/R/handlers.R

@@ -38,7 +38,7 @@ prompt_download <- function(package, show_menu) {
 
  if (download == 1) {
  webr::install(package)
- return(invisible(TRUE))
+ return(invisible(length(find.package(package, quiet = TRUE)) > 0))
  }
 
  return(invisible(FALSE))

packages/webr/R/library.R

@@ -28,8 +28,10 @@
 library_shim <- function(pkg, ..., show_menu = getOption("webr.show_menu")) {
  show_menu <- ifelse(is.null(show_menu), FALSE, show_menu)
  package <- as.character(substitute(pkg))
- if (!base::require(package, character.only = TRUE, quietly = TRUE)) {
- prompt_download(package, show_menu)
+ if (length(find.package(package, quiet = TRUE)) == 0) {
+ if (!prompt_download(package, show_menu)) {
+ return(invisible(NULL))
+ }
  }
  base::library(package, character.only = TRUE, ...)
 }
@@ -39,8 +41,10 @@ library_shim <- function(pkg, ..., show_menu = getOption("webr.show_menu")) {
 require_shim <- function(pkg, ..., show_menu = getOption("webr.show_menu")) {
  show_menu <- ifelse(is.null(show_menu), FALSE, show_menu)
  package <- as.character(substitute(pkg))
- if (!base::require(package, character.only = TRUE, quietly = TRUE)) {
- prompt_download(package, show_menu)
+ if (length(find.package(package, quiet = TRUE)) == 0) {
+ if (!prompt_download(package, show_menu)) {
+ return(invisible(NULL))
+ }
  }
  base::require(package, character.only = TRUE, ...)
 }