for Rnw documents, suppress the extra paragraph break at the end of the chunk (#1958)

Author: krivit

NEWS.md

@@ -16,6 +16,10 @@
 
 - For Rnw documents, the commented `%\begin{document}` will no longer cause trouble (thanks, @NewbieKnitter @shrektan, #1819).
 
+## MINOR CHANGES
+
+- For Rnw documents, if a chunk's output ends with `\n`, **knitr** will no longer add another `\n` to it (thanks, @krivit #1958, @jpritikin 1092).
+
 # CHANGES IN knitr VERSION 1.31
 
 ## NEW FEATURES

R/hooks-latex.R

@@ -191,7 +191,13 @@ hook_plot_tex = function(x, options) {
   k2 = '\\end{kframe}'
   x = .rm.empty.envir(paste0(k1, x, k2))
   size = if (options$size == 'normalsize') '' else sprintf('\\%s', options$size)
-  if (!ai) x = sprintf('\\begin{knitrout}%s\n%s\n\\end{knitrout}', size, x)
+  if (!ai) {
+    # if the chunk content starts with \n, don't add \n; similarly, if it ends with \n, don't append \n
+    n1 = n2 = '\n'
+    if (grepl('^\\s*\n', x)) n1 = ''
+    if (grepl('\n\\s*$', x)) n2 = ''
+    x = sprintf('\\begin{knitrout}%s%s%s%s\\end{knitrout}', size, n1, x, n2)
+  }
   if (options$split) {
     name = fig_path('.tex', options, NULL)
     if (!file.exists(dirname(name)))