[Rd] possible bug in utils::removeSource - NULL argument is silently dropped

[Dénes Tóth]

Dear R-Core Team,

I found an unexpected behaviour in utils::removeSource (also present in 
r-devel as of today).

---

# create a function which accepts NULL argument
foo <- function(x, y) {
   if (is.null(y)) y <- "default foo"
   attr(x, "foo") <- y
   x
}

# create a function which utilizes 'foo'
testSrc <- function() {
   x <- 1:3
   x <- foo(x, NULL)
   x
}

# this works fine
testSrc()

# this fails
testNoSrc <- utils::removeSource(testSrc)
testNoSrc()

# removeSource removes NULL from the 'foo' call
print(testNoSrc)

---

I traced back the bug to this row in removeSource:

(line 33 in sourceutils.R)
part[[i]] <- recurse(part[[i]])

it should be (IMHO):
part[i] <- list(recurse(part[[i]]))

---

# create a function with the above patch
rmSource <- function (fn) {
   stopifnot(is.function(fn))
   if (is.primitive(fn))
     return(fn)
   attr(fn, "srcref") <- NULL
   attr(body(fn), "wholeSrcref") <- NULL
   attr(body(fn), "srcfile") <- NULL
   recurse <- function(part) {
     if (is.name(part))
       return(part)
     attr(part, "srcref") <- NULL
     attr(part, "wholeSrcref") <- NULL
     attr(part, "srcfile") <- NULL
     if (is.language(part) && is.recursive(part)) {
       for (i in seq_along(part))
         part[i] <- list(recurse(part[[i]]))
     }
     part
   }
   body(fn) <- recurse(body(fn))
   fn
}

# test
( testNoSrc2 <- rmSource(testSrc) )
testNoSrc2()


Regards,
Denes