Isolate side effects in graphics functions

NEWS.md

@@ -7,6 +7,11 @@
 * Use code to generate the Unicode/LaTeX mapping table, to replace the previous
   `R/sysdata.rda` solution. Now the mapping table is directly accessible
   via `r2rtf:::unicode_latex` (thanks, @yihui, #218).
+* Introduce "safe" versions of `graphics::par()` and `graphics::strwidth()`
+  that isolate their side effects by evaluating within a temporary BMP device.
+  This should avoid the generation of `Rplots.pdf` when when running r2rtf code
+  in certain context such as clicking the test buttons in RStudio environments
+  (#227).
 
 # r2rtf 1.1.1
 

R/rtf_strwidth.R

@@ -53,7 +53,7 @@ rtf_strwidth <- function(tbl) {
   }
 
   # Font size
-  text_cex <- attr(tbl, "text_font_size") / graphics::par("ps")
+  text_cex <- attr(tbl, "text_font_size") / safe_par("ps")
 
   # Font format
   # text format 1 (plain/normal), 2 (bold), 3 (italic), 4 (bold-italic)
@@ -107,7 +107,8 @@ rtf_strwidth <- function(tbl) {
       grDevices::windowsFonts("Courier" = grDevices::windowsFont("Courier New"))
     }
 
-    x$width <- graphics::strwidth(x$text,
+    x$width <- safe_strwidth(
+      x$text,
       units = "inches",
       cex = x$cex[1],
       font = x$font[1],
@@ -131,3 +132,37 @@ rtf_strwidth <- function(tbl) {
 
   width
 }
+
+#' Safe version of `graphics::par()` with side effects isolated
+#'
+#' @noRd
+safe_par <- function(...) with_bmp(graphics::par(...))
+
+#' Safe version of `graphics::strwidth()` with side effects isolated
+#'
+#' @noRd
+safe_strwidth <- function(text, ...) with_bmp(graphics::strwidth(text, ...))
+
+#' Evaluate expression within a BMP device and close it on exit
+#'
+#' See why: <https://github.com/Merck/r2rtf/issues/227>
+#'
+#' @noRd
+with_bmp <- function(expr) {
+  expr <- substitute(expr)
+  grDevices::bmp(file_null())
+  on.exit(
+    {
+      current <- grDevices::dev.cur()
+      if (current > 1) {
+        prev <- grDevices::dev.prev(current)
+        grDevices::dev.off(current)
+        if (prev != current) grDevices::dev.set(prev)
+      }
+    },
+    add = TRUE
+  )
+  eval(expr, envir = parent.frame())
+}
+
+file_null <- function() if (.Platform$OS.type == "windows") "nul:" else "/dev/null"

tests/testthat/test-developer-testing-safe-graphics.R

@@ -0,0 +1,9 @@
+test_that("Running graphics functions within with_bmp() does not affect graphics device", {
+  dev_cur <- grDevices::dev.cur()
+
+  with_bmp(par("mar"))
+  safe_par("font")
+  safe_strwidth("Hello world!", units = "inches", cex = 1, font = 1, family = "sans")
+
+  expect_equal(grDevices::dev.cur(), dev_cur)
+})

tests/testthat/test-independent-testing-rtf_nrow.R

@@ -76,8 +76,8 @@ cellsize <- matrix(width, nrow = nrow(tbl), ncol = ncol(tbl), byrow = TRUE) - pa
 nline_vector <- rtf_nline_vector(
   text = c("title 1", "this is a sentence for title 2", NA),
   strwidth = c(
-    strwidth("title 1", units = "inches"),
-    strwidth("this is a sentence for title 2", units = "inches")
+    safe_strwidth("title 1", units = "inches"),
+    safe_strwidth("this is a sentence for title 2", units = "inches")
   ),
   size = 0.5
 )

tests/testthat/test-independent-testing-rtf_strwidth.R

@@ -15,14 +15,16 @@ tbl <- df |>
 
 strw <- round(r2rtf:::rtf_strwidth(tbl), 5)
 
-size8italic <- round(graphics::strwidth("This is a long sentence",
+size8italic <- round(safe_strwidth(
+  "This is a long sentence",
   units = "inches",
   cex = 2 / 3,
   font = 3,
   family = "Times"
 ), 5)
 
-bold <- round(graphics::strwidth("third",
+bold <- round(safe_strwidth(
+  "third",
   units = "inches",
   cex = 2 / 3,
   font = 2,