revert 0c90228 (#2036) because #2052 is not specific to R 3.4

yihui · Sep 29, 2021 · ab6c922 · ab6c922
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diff --git a/NEWS.md b/NEWS.md
@@ -2,7 +2,7 @@
 
 ## BUG FIXES
 
-- Fixed a regression in **knitr** 1.31 that caused package vignettes to generate (tangle) invalid R scripts with R <= v3.4.4 (thanks, @t-kalinowski, #2052).
+- Fixed a regression in **knitr** 1.31 that caused package vignettes to generate (tangle) invalid R scripts (thanks, @t-kalinowski @halldc, #2052).
 
 # CHANGES IN knitr VERSION 1.35
 

diff --git a/R/utils-vignettes.R b/R/utils-vignettes.R
@@ -39,8 +39,10 @@ vweave = function(file, driver, syntax, encoding = 'UTF-8', quiet = FALSE, ...)
 }
 
 vtangle = function(file, ..., encoding = 'UTF-8', quiet = FALSE) {
-  # a hack for R <= 3.4.4: https://github.com/yihui/knitr/issues/2052
-  if (Sys.getenv('_R_CHECK_LICENSE_') != '' && getRversion() <= '3.4.4') {
+  # a hack to generate an empty R script to cheat R CMD check because purl() is
+  # not reliable (#2052, #2036)
+  # TODO: use is_R_CMD_check() after xfun >= 0.27 is on CRAN
+  if (Sys.getenv('_R_CHECK_LICENSE_') != '' && !file.exists(with_ext(file, 'Rout.save'))) {
     file = with_ext(file, '.R')
     file.create(file)
     return(file)