R/zzz.R

In vegawidget: 'Htmlwidget' for 'Vega' and 'Vega-Lite'

# copied from vctrs: https://github.com/r-lib/vctrs/blob/master/R/register-s3.R

#' Register an s3 method
#'
#' This is a reimplementation of `vctrs::s3_register()`, implemented here
#' to avoid having to take a dependency on vctrs.
#'
#' @param generic Name of the generic in the form `pkg::generic`.
#' @param class Name of the class
#' @param method Optionally, the implementation of the method. By default,
#'   this will be found by looking for a function called `generic.class`
#'   in the package environment.
#'
#'   Note that providing `method` can be dangerous if you use
#'   devtools. When the namespace of the method is reloaded by
#'   `devtools::load_all()`, the function will keep inheriting from
#'   the old namespace. This might cause crashes because of dangling
#'   `.Call()` pointers.
#'
#' @return Invisible `NULL`, called for side effects.
#'
#' @export
#' @keywords internal
#'
s3_register <- function(generic, class, method = NULL) {
  stopifnot(is.character(generic), length(generic) == 1)
  stopifnot(is.character(class), length(class) == 1)

  pieces <- strsplit(generic, "::")[[1]]
  stopifnot(length(pieces) == 2)
  package <- pieces[[1]]
  generic <- pieces[[2]]

  caller <- parent.frame()

  get_method_env <- function() {
    top <- topenv(caller)
    if (isNamespace(top)) {
      asNamespace(environmentName(top))
    } else {
      caller
    }
  }
  get_method <- function(method, env) {
    if (is.null(method)) {
      get(paste0(generic, ".", class), envir = get_method_env())
    } else {
      method
    }
  }

  register <- function(...) {
    envir <- asNamespace(package)

    # Refresh the method each time, it might have been updated by
    # `devtools::load_all()`
    method_fn <- get_method(method)
    stopifnot(is.function(method_fn))


    # Only register if generic can be accessed
    if (exists(generic, envir)) {
      registerS3method(generic, class, method_fn, envir = envir)
    } else if (identical(Sys.getenv("NOT_CRAN"), "true")) {
      warning(sprintf(
        "Can't find generic `%s` in package %s to register S3 method.",
        generic,
        package
      ))
    }
  }

  # Always register hook in case package is later unloaded & reloaded
  setHook(packageEvent(package, "onLoad"), register)

  # Avoid registration failures during loading (pkgload or regular)
  if (isNamespaceLoaded(package)) {
    register()
  }

  invisible()
}

# keep track of which widget (e.g. "vl5", "vl4") we are using
vw_env <- rlang::env(rlang::empty_env())

.onLoad <- function(...) {
  s3_register("knitr::knit_print", "vegaspec")
  vw_env$widget = .widget_default # set default
  vw_env$is_locked = FALSE
}