modified print function is not called from script in package directory

[swhalemwo]

I'm using a custom function for printing data.table objects, which basically prints them with the formatting of tibbles.

print.data.table <- function(x, ...) {
  ans <- x
  attr(ans, "row.names") <- .set_row_names(nrow(x))
  attr(ans, "class") <- c("tbl", "data.frame")
  attr(ans, "sorted") <- NULL
  attr(ans, ".internal.selfref") <- NULL
  print(ans, ...)
invisible(x)
}

This has so far worked fine, but I've recently started writing my own package, in which many functions return data.table objects. When I call these functions from a script in my package directory, my custom print.data.table function isn't used, but the original one provided by data.table.

fx <- function() {
  as.data.table(mtcars)
}

calling fx from a script file (with ess-eval-line/C-j) doesn't apply my custom print.data.table function (output below).

> > fx()
     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
 1: 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
 2: 21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
 3: 22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
 4: 21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
 5: 18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
 6: 18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
 7: 14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
 8: 24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
 9: 22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
10: 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4
11: 17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
12: 16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3
13: 17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3
14: 15.2   8 275.8 180 3.07 3.780 18.00  0  0    3    3
15: 10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4
16: 10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4
17: 14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4
18: 32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
19: 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
20: 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
# more lines here

However, calling it in terminal/R process buffer directly applies my print.data.table function correctly:

> fx()
# A data frame: 32 × 11
     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
 1  21       6  160    110  3.9   2.62  16.5     0     1     4     4
 2  21       6  160    110  3.9   2.88  17.0     0     1     4     4
 3  22.8     4  108     93  3.85  2.32  18.6     1     1     4     1
 4  21.4     6  258    110  3.08  3.22  19.4     1     0     3     1
 5  18.7     8  360    175  3.15  3.44  17.0     0     0     3     2
 6  18.1     6  225    105  2.76  3.46  20.2     1     0     3     1
 7  14.3     8  360    245  3.21  3.57  15.8     0     0     3     4
 8  24.4     4  147.    62  3.69  3.19  20       1     0     4     2
 9  22.8     4  141.    95  3.92  3.15  22.9     1     0     4     2
10  19.2     6  168.   123  3.92  3.44  18.3     1     0     4     4
# ℹ 22 more rows
# ℹ Use `print(n = ...)` to see more rows

This is also the output I get when calling it from a script file which is not inside a package directory.

When calling fx() from a script, there are also two chevrons (">") in the terminal output. However, this seems to be at most a side effect, since when I execute a region I get a single chevron for each statement, but still my print.data.table function isn't used:

10
fx()

results in

> 10
[1] 10
> fx()
     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
 1: 21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
 2: 21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
 3: 22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
 4: 21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
 5: 18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
# more rows

Turning off ess-r-package-mode doesn't change this, nor does setting ess-r-package-auto-activate or ess-r-package-auto-enable-namespaced-evaluation to nil, and in Rstudio this problem does not occur. I have for now recompiled data.table with my print.data.table function instead of the original function (which isn't a big hassle since there are few data.table updates these days), but it's still a hacky band aid. Any ideas of what's going here or how to fix this?