funSource.R

#' Source code of a function
#' 
#' open source code of a function in a loaded or specified package on 
#' github.com/cran or github.com/wch/r-source
#' 
#' @return links that are also opened with \code{\link{browseURL}}
#' @author Berry Boessenkool, \email{berry-b@@gmx.de}, Jan+Dec 2016, May 2017, April 2019
#' @importFrom utils browseURL find getAnywhere
#' @export
#' @seealso \url{https://github.com/brry/rskey#rskey} to add this as a keyboard shortcut
#' @examples
#' \dontrun{ ## browser windows should not be opened in CRAN checks
#' funSource("head")
#' funSource(message()) # handles brackets if fun can be evaluated without input
#' funSource("require", local=TRUE) # usefull when offline
#' 
#' funSource("OSMscale::earthDist") # works even for non-installed CRAN packages
#' 
#' is.error(funSource("earthDist"), TRUE, TRUE) # Error for unloaded package
#' require(plotrix); require(scales)
#' funSource(rescale) # from the last loaded package
#' 
#' tail <- function(...) stop("This is a dummy function. Type: rm(tail)")
#' funSource("tail")
#' rm(tail)
#' }
#' 
#' @param x              Function name, with or without quotation marks.
#'                       Trailing brackets are removed: \code{xx()} -> \code{"xx"}.\cr
#'                       Can be \code{package::function}, which must be quoted for
#'                       non-loaded packages.
#' @param character.only If TRUE, look for \code{SomeFun} instead of \code{MyFun}
#'                       in case \code{MyFun <- "SomeFun"}. 
#'                       DEFAULT: \code{\link{is.character}(x)}
#' @param local          Open offline version of the code? Lacks comments and
#'                       original formatting of source code. DEFAULT: FALSE
#' 
funSource <- function(
x,
character.only=is.character(x),
local=FALSE
)
{
# change input to character:
xname <- deparse(substitute(x))
xname <- gsub('"', "", xname)
if(!character.only) x <- xname
if(length(x)>1) stop("length(x) must be 1, not ", length(x))

# remove empty brackets at the end:
x <- sub("\\(\\)$", "", x)

# check input for non-valid characters in function names:
if(grepl("[^[:alnum:]|^_|^.|^:]", x)) 
warning("funSource accepts only a function name as input (without brackets etc).\n",
        "The code will be tried anyway, but expect an error.", 
        immediate.=TRUE, call.=FALSE)

# Get package name -------------------------------------------------------------

# if package is specified: -----
if(grepl("::", x))
  {
  pn <- strsplit(x, "::")[[1]][1]
  x  <- strsplit(x, "::")[[1]][2]
  } else
{
# find locations of x: -----
locs <- find(x)
if(length(locs)<1) stop("A package containing '", x,"' was not found on the search path.")
if(locs[1]==".GlobalEnv")
  {
  warning(x," exists in .GlobalEnv, is ignored.")
  locs <- locs[-1]
  }
# get package name
pn <- strsplit(locs, ":")
pn <- sapply(pn, "[", 2)
if(all(is.na(pn))) stop("A package containing '", x,"' was not found on the search path.")
if(length(pn)>1)
  {
  warning("Using ", x, " in ", pn[1], ". It was also found in ", toString(pn[-1]))
  pn <- pn[1]
  }
}

# return offline function content ----------------------------------------------
# reformatted by R, not original source
if(local)
  {
  File <- paste0(tempdir(), "/", xname, ".R")
  dd <- getAnywhere(x)
  sink(File)
  print(dd$objs[[1L]])
  sink()
  # Open the file with the program associated with its file extension
  message("Now opening (in default viewer): ", File)
  openFile(File)
  return(invisible(File))
  }

# select mirror (base R or CRAN) -----------------------------------------------

if(pn %in% c("base", "compiler", "datasets", "grDevices", "graphics", "grid",
             "methods", "parallel", "profile", "splines", "stats", "stats4",
             "tcltk", "tools", "translations", "utils"))
  {
  baselink <- "https://github.com/wch/r-source/tree/trunk/src/library/"
  finallink <- paste0(baselink,pn,"/R/", x,".R")
  slink <- paste0("wch/r-source+path:src/library/",pn,"/R")
  } else
  {
  baselink <- "https://github.com/cran/"
  finallink <- paste0(baselink,pn,"/blob/master/R/", x,".R")
  slink <- paste0("cran/",pn,"+path:R")
  }

# open link in Browser ---------------------------------------------------------

# Search github repo query link
searchlink <- paste0("https://github.com/search?q=",x," function repo:",slink)

# little helper function to determine existence of a link:
canBeRead <- function(url)
 {
 rl <- suppressWarnings(try(readLines(url, n=1), silent=TRUE))
 !inherits(rl, "try-error")
 }

# Option 1: If the link can be read, open it in the browser and return output:
if(canBeRead(finallink)) 
 {
 browseURL(finallink) 
 return(c(searchlink, finallink))
 }

# Option 2: Try with lowercase r:
finallink <- sub("\\.R$", '\\.r', finallink)
if(canBeRead(finallink)) 
 {
 browseURL(finallink) 
 return(c(searchlink, finallink))
 }

# Option 3: open the searchlink:
# this would also occur if R has no internet acces, but the browser does
browseURL(searchlink)
return(searchlink)

}