ox-md, ox-ascii, ox-texinfo: Strip blank lines from paragraphs

* lisp/org-macs.el (org-remove-blank-lines): New helper function to
strip blank lines from string.
* lisp/ox-ascii.el (org-ascii-paragraph):
* lisp/ox-latex.el (org-latex-paragraph):
* lisp/ox-md.el (org-md-paragraph):
* lisp/ox-texinfo.el (org-texinfo-paragraph): Strip blank lines from
paragraphs - these exporters are using blank lines as paragraph
separators.

Reported-by: Max Nikulin <manikulin@gmail.com>
Link: https://orgmode.org/list/v00le7$frp$1@ciao.gmane.io

lisp/org-macs.el

@@ -1290,6 +1290,10 @@ Assumes that s is a single line, starting in column 0."
 	     t t s)))
   s)
 
+(defun org-remove-blank-lines (s)
+  "Remove blank lines in S."
+  (replace-regexp-in-string (rx "\n" (1+ (0+ space) "\n")) "\n" s))
+
 (defun org-wrap (string &optional width lines)
   "Wrap string to either a number of lines, or a width in characters.
 If WIDTH is non-nil, the string is wrapped to that width, however many lines

lisp/ox-ascii.el

@@ -1652,6 +1652,12 @@ information."
   "Transcode a PARAGRAPH element from Org to ASCII.
 CONTENTS is the contents of the paragraph, as a string.  INFO is
 the plist used as a communication channel."
+  ;; Ensure that we do not create multiple paragraphs, when a single
+  ;; paragraph is expected.
+  ;; Multiple newlines may appear in CONTENTS, for example, when
+  ;; certain objects are stripped from export, leaving single newlines
+  ;; before and after.
+  (setq contents (org-remove-blank-lines contents))
   (org-ascii--justify-element
    (let ((indented-line-width (plist-get info :ascii-indented-line-width)))
      (if (not (wholenump indented-line-width)) contents

lisp/ox-latex.el

@@ -3050,9 +3050,7 @@ the plist used as a communication channel."
   ;; Multiple newlines may appear in CONTENTS, for example, when
   ;; certain objects are stripped from export, leaving single newlines
   ;; before and after.
-  (replace-regexp-in-string
-   (rx "\n" (1+ (0+ space) "\n")) "\n"
-   contents))
+  (org-remove-blank-lines contents))
 
 
 ;;;; Plain List

lisp/ox-md.el

@@ -633,6 +633,12 @@ information."
   "Transcode PARAGRAPH element into Markdown format.
 CONTENTS is the paragraph contents.  INFO is a plist used as
 a communication channel."
+  ;; Ensure that we do not create multiple paragraphs, when a single
+  ;; paragraph is expected.
+  ;; Multiple newlines may appear in CONTENTS, for example, when
+  ;; certain objects are stripped from export, leaving single newlines
+  ;; before and after.
+  (setq contents (org-remove-blank-lines contents))
   (let ((first-object (car (org-element-contents paragraph))))
     ;; If paragraph starts with a #, protect it.
     (if (and (stringp first-object) (string-prefix-p "#" first-object))

lisp/ox-texinfo.el

@@ -1517,7 +1517,12 @@ information."
   "Transcode a PARAGRAPH element from Org to Texinfo.
 CONTENTS is the contents of the paragraph, as a string.  INFO is
 the plist used as a communication channel."
-  contents)
+  ;; Ensure that we do not create multiple paragraphs, when a single
+  ;; paragraph is expected.
+  ;; Multiple newlines may appear in CONTENTS, for example, when
+  ;; certain objects are stripped from export, leaving single newlines
+  ;; before and after.
+  (org-remove-blank-lines contents))
 
 ;;;; Plain List