fix #63: check package availability in advance

in the case of R CMD check, also send a reminder to add the package to DESCRIPTION

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: xfun
 Type: Package
 Title: Supporting Functions for Packages Maintained by 'Yihui Xie'
-Version: 0.30.2
+Version: 0.30.3
 Authors@R: c(
   person("Yihui", "Xie", role = c("aut", "cre", "cph"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
   person("Wush", "Wu", role = "ctb"),

R/base64.R

@@ -71,12 +71,17 @@ base64_encode_r = function(x) {
 #' can be used to embed data in HTML documents, e.g., in the \code{src}
 #' attribute of the \verb{<img />} tag.
 #' @param x A file path.
+#' @param type The MIME type of the file, e.g., \code{"image/png"} for a PNG
+#'   image file.
 #' @return A string of the form \verb{data:<media type>;base64,<data>}.
+#' @note By default, this function requires the \pkg{mime} package to determine
+#'   the MIME type of the file.
 #' @export
 #' @examples
 #' logo = xfun:::R_logo()
 #' img = htmltools::img(src = xfun::base64_uri(logo), alt = 'R logo')
 #' if (interactive()) htmltools::browsable(img)
-base64_uri = function(x) {
-  paste0("data:", mime::guess_type(x), ";base64,", base64_encode(x))
+base64_uri = function(x, type = mime::guess_type(x)) {
+  if (missing(type)) pkg_require('mime')
+  paste0("data:", type, ";base64,", base64_encode(x))
 }

R/markdown.R

@@ -143,6 +143,7 @@ escape_math = function(x) {
 #' link
 #' if (interactive()) htmltools::browsable(link)
 embed_file = function(path, name = basename(path), text = paste('Download', name), ...) {
+  pkg_require(c('mime', 'htmltools'))
   h = paste0("data:", mime::guess_type(path), ";base64,", base64_encode(path))
   htmltools::a(text, href = h, download = name, ...)
 }

R/packages.R

@@ -105,6 +105,17 @@ pkg_attach2 = function(...) pkg_attach(..., install = TRUE)
 #' @export
 pkg_load2 = function(...) pkg_load(..., install = TRUE)
 
+pkg_require = function(pkgs, which = length(sys.calls()) - 1) {
+  f = func_name(which)
+  for (p in pkgs) if (!loadable(p)) stop2(
+    "The '", p, "' package is required by the function '", f, "' but not available.",
+    if (is_R_CMD_check()) c(
+      " If you are developing an R package, you need to declare the dependency on '",
+      p, "' in the DESCRIPTION file (e.g., in 'Imports')."
+    )
+  )
+}
+
 pkg_update = function(...) {
   update.packages(ask = FALSE, checkBuilt = TRUE, ...)
 }

R/utils.R

@@ -292,3 +292,9 @@ format_bytes = function(x, units = 'auto', ...) {
     format(structure(b, class = 'object_size'), units = units, ...)
   }, character(1))
 }
+
+# get the function name of the parent call
+func_name = function(which = 1) {
+  x = sys.call(which)[[1]]
+  deparse(x)[1]
+}