fix #2166: reset the graphics device after each knit() call

dev.off() will move the device to dev.next(), but the next device is not necessarily the one previously opened, so we have to precisely reset to that specific device

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: knitr
 Type: Package
 Title: A General-Purpose Package for Dynamic Report Generation in R
-Version: 1.40.1
+Version: 1.40.2
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
     person("Abhraneel", "Sarma", role = "ctb"),

NEWS.md

@@ -2,6 +2,8 @@
 
 ## BUG FIXES
 
+- Plot created outside of `knit()` could sneak into `knit_child()` results (thanks, @niklaswillrich, #2166).
+
 - User-provided background colors for code chunks in `.Rnw` documents may fail (thanks, @nielsrhansen, #2167).
 
 # CHANGES IN knitr VERSION 1.40

R/block.R

@@ -201,6 +201,7 @@ eng_r = function(options) {
   # open a device to record plots if not using a global device or no device is
   # open, and close this device if we don't want to use a global device
   if (!opts_knit$get('global.device') || is.null(dev.list())) {
+    dv0 = dev.cur(); on.exit(dev.set(dv0), add = TRUE)  # reset current device (#2166)
     chunk_device(options, keep != 'none', tmp.fig)
     dv = dev.cur()
     if (!opts_knit$get('global.device')) on.exit(dev.off(dv), add = TRUE)