ox-latex: Remove org-latex-line-break-safe

This reverts commit 3f60acff77 and
subsequent relevant comments.

* lisp/ox-latex.el (org-latex-line-break-safe): Remove constant.  The
\\[0pt] is actually not safe to use in some scenarios. We use a
different approach to avoid plain text [...] being interpreted as
LaTeX optional argument - we escape [ like {[}; that's what pandoc
does.
(org-latex-clock):
(org-latex-line-break):
(org-latex-plain-text):
(org-latex-planning):
(org-latex--org-table):
(org-latex--math-table):
(org-latex-table-row):
(org-latex-verse-block):
* testing/lisp/test-org-table.el (test-org-table/to-latex):
* testing/lisp/test-ox-latex.el (test-ox-latex/verse):
(test-ox-latex/longtable): Remove references to
`org-latex-line-break-safe'.
* etc/ORG-NEWS (=ox-latex=: ~org-latex-line-break-safe~ is removed):
Announce removal.
* lisp/org-compat.el (org-latex-line-break-safe): Make obsolete.

Link: https://orgmode.org/list/878r4jg37s.fsf@posteo.net

etc/ORG-NEWS

@@ -13,6 +13,16 @@ Please send Org bug reports to mailto:emacs-orgmode@gnu.org.
 
 * Version 9.7 (not released yet)
 ** Important announcements and breaking changes
+*** =ox-latex=: ~org-latex-line-break-safe~ is deprecated
+
+~org-latex-line-break-safe~ constant was previously introduced to deal
+with edge cases when LaTeX interprets [...] as LaTeX command
+argument.  However, it caused a number of other issues and proved
+itself not to be as "safe" as it supposed to be.
+
+We now use a Pandoc's approach to deal with the same problem,
+utilizing ={[}= to escape =[...]= instances where needed.
+
 *** ob-python now sets ~python-shell-buffer-name~ in Org edit buffers
 
 When editing a Python src block, the editing buffer is now associated

lisp/org-compat.el

@@ -629,6 +629,24 @@ Counting starts at 1."
 (define-obsolete-function-alias 'org-file-url-p 'org-url-p "9.6")
 (define-obsolete-variable-alias 'org-plantuml-executable-args 'org-plantuml-args
   "Org 9.6")
+
+(defconst org-latex-line-break-safe "\\\\[0pt]"
+  "Linebreak protecting the following [...].
+
+Without \"[0pt]\" it would be interpreted as an optional argument to
+the \\\\.
+
+This constant, for example, makes the below code not err:
+
+\\begin{tabular}{c|c}
+    [t] & s\\\\[0pt]
+    [I] & A\\\\[0pt]
+    [m] & kg
+\\end{tabular}")
+(make-obsolete 'org-latex-line-break-safe
+               "should not be used - it is not safe in all the scenarios."
+               "9.7")
+
 (defun org-in-fixed-width-region-p ()
   "Non-nil if point in a fixed-width region."
   (save-match-data

lisp/ox-latex.el

@@ -298,23 +298,10 @@ cdr is a property list.  Valid keywords for this list can be:
 - `:script-tag' the script otf tag.")
 
 
-(defconst org-latex-line-break-safe "\\\\[0pt]"
-  "Linebreak protecting the following [...].
 
-Without \"[0pt]\" it would be interpreted as an optional argument to
-the \\\\.
-
-This constant, for example, makes the below code not err:
-
-\\begin{tabular}{c|c}
-    [t] & s\\\\[0pt]
-    [I] & A\\\\[0pt]
-    [m] & kg
-\\end{tabular}")
-
-(defconst org-latex-table-matrix-macros `(("bordermatrix" . "\\cr")
+(defconst org-latex-table-matrix-macros '(("bordermatrix" . "\\cr")
 					  ("qbordermatrix" . "\\cr")
-					  ("kbordermatrix" . ,org-latex-line-break-safe))
+					  ("kbordermatrix" . "\\\\"))
   "Alist between matrix macros and their row ending.")
 
 (defconst org-latex-math-environments-re
@@ -2124,7 +2111,7 @@ information."
 	   (concat (org-timestamp-translate (org-element-property :value clock))
 		   (let ((time (org-element-property :duration clock)))
 		     (and time (format " (%s)" time)))))
-   org-latex-line-break-safe))
+   "\\\\"))
 
 
 ;;;; Code
@@ -2722,7 +2709,7 @@ CONTENTS is nil.  INFO is a plist holding contextual information."
 (defun org-latex-line-break (_line-break _contents _info)
   "Transcode a LINE-BREAK object from Org to LaTeX.
 CONTENTS is nil.  INFO is a plist holding contextual information."
-  (concat org-latex-line-break-safe "\n"))
+  "\\\\\n")
 
 
 ;;;; Link
@@ -3092,9 +3079,7 @@ contextual information."
     ;; Handle break preservation if required.
     (when (plist-get info :preserve-breaks)
       (setq output (replace-regexp-in-string
-		    "\\(?:[ \t]*\\\\\\\\\\)?[ \t]*\n"
-                    (concat org-latex-line-break-safe "\n")
-                    output nil t)))
+		    "\\(?:[ \t]*\\\\\\\\\\)?[ \t]*\n" "\\\\\n" output nil t)))
     ;; Protect [foo] at the beginning of lines / beginning of the
     ;; plain-text object.  This prevents LaTeX from unexpectedly
     ;; interpreting @@latex:\pagebreak@@ [foo] as a command with
@@ -3139,7 +3124,7 @@ information."
 		(format (plist-get info :latex-active-timestamp-format)
 			(org-timestamp-translate scheduled)))))))
     " ")
-   org-latex-line-break-safe))
+   "\\\\"))
 
 
 ;;;; Property Drawer
@@ -3919,11 +3904,11 @@ This function assumes TABLE has `org' as its `:type' property and
 		(format "\\begin{%s}%s{%s}\n" table-env width alignment)
 		(and above?
 		     (org-string-nw-p caption)
-		     (concat caption org-latex-line-break-safe "\n"))
+		     (concat caption "\\\\\n"))
 		contents
 		(and (not above?)
 		     (org-string-nw-p caption)
-		     (concat caption org-latex-line-break-safe "\n"))
+		     (concat caption "\\\\\n"))
 		(format "\\end{%s}" table-env)
 		(and fontsize "}"))))
      (t
@@ -4008,7 +3993,7 @@ This function assumes TABLE has `org' as its `:type' property and
 		 (lambda (cell)
 		   (substring (org-element-interpret-data cell) 0 -1))
 		 (org-element-map row 'table-cell #'identity info) "&")
-		(or (cdr (assoc env org-latex-table-matrix-macros)) org-latex-line-break-safe)
+		(or (cdr (assoc env org-latex-table-matrix-macros)) "\\\\")
 		"\n")))
 	   (org-element-map table 'table-row #'identity info) "")))
     (concat
@@ -4083,7 +4068,7 @@ a communication channel."
             (setq table-head-cache (make-hash-table :test #'eq))
             (plist-put info :org-latex-table-head-cache table-head-cache))
           (if-let ((head-contents (gethash (org-element-parent table-row) table-head-cache)))
-              (puthash (org-element-parent table-row) (concat head-contents org-latex-line-break-safe "\n" contents)
+              (puthash (org-element-parent table-row) (concat head-contents "\\\\\n" contents)
                        table-head-cache)
             (puthash (org-element-parent table-row) contents table-head-cache))))
       ;; Return LaTeX string as the transcoder.
@@ -4092,7 +4077,7 @@ a communication channel."
        ;; hline was specifically marked.
        (and booktabsp (not (org-export-get-previous-element table-row info))
 	    "\\toprule\n")
-       contents org-latex-line-break-safe "\n"
+       contents "\\\\\n"
        (cond
 	;; Special case for long tables.  Define header and footers.
 	((and longtablep (org-export-table-row-ends-header-p table-row info))
@@ -4100,9 +4085,9 @@ a communication channel."
 			      (org-element-lineage table-row 'table) info))))
 	   (format "%s
 \\endfirsthead
-\\multicolumn{%d}{l}{%s} \\\\[0pt]
+\\multicolumn{%d}{l}{%s} \\\\
 %s
-%s \\\\[0pt]\n
+%s \\\\\n
 %s
 \\endhead
 %s\\multicolumn{%d}{r}{%s} \\\\
@@ -4211,15 +4196,15 @@ contextual information."
 	       (replace-regexp-in-string
                 (if (not lit)
 		    (rx-to-string
-                     `(seq (group ,org-latex-line-break-safe "\n")
-		           (1+ (group line-start (0+ space) ,org-latex-line-break-safe "\n"))))
-		  (concat "^[ \t]*" (regexp-quote org-latex-line-break-safe) "$"))
+                     `(seq (group "\\\\\n")
+		           (1+ (group line-start (0+ space) "\\\\\n"))))
+		  "^[ \t]*\\\\$")
 	        (if (not lit)
 		    (if lin "\\\\!\n\n" "\n\n")
 		  "\\vspace*{\\baselineskip}")
 	        (replace-regexp-in-string
 	         "\\([ \t]*\\\\\\\\\\)?[ \t]*\n"
-                 (concat org-latex-line-break-safe "\n")
+                 "\\\\\n"
 	         (if (not lit)
 		     (concat (org-trim contents t) "\n")
 		   contents)

testing/lisp/test-org-table.el

@@ -1633,11 +1633,11 @@ See also `test-org-table/copy-field'."
 (ert-deftest test-org-table/to-latex ()
   "Test `orgtbl-to-latex' specifications."
   (should
-   (equal "\\begin{tabular}{l}\na\\\\[0pt]\n\\end{tabular}"
+   (equal "\\begin{tabular}{l}\na\\\\\n\\end{tabular}"
 	  (orgtbl-to-latex (org-table-to-lisp "| a |") nil)))
   ;; Test :environment parameter.
   (should
-   (equal "\\begin{tabularx}{l}\na\\\\[0pt]\n\\end{tabularx}"
+   (equal "\\begin{tabularx}{l}\na\\\\\n\\end{tabularx}"
 	  (orgtbl-to-latex (org-table-to-lisp "| a |")
 			   '(:environment "tabularx"))))
   ;; Test :booktabs parameter.
@@ -1646,7 +1646,7 @@ See also `test-org-table/copy-field'."
     "\\toprule" (orgtbl-to-latex (org-table-to-lisp "| a |") '(:booktabs t))))
   ;; Handle LaTeX snippets.
   (should
-   (equal "\\begin{tabular}{l}\n\\(x\\)\\\\[0pt]\n\\end{tabular}"
+   (equal "\\begin{tabular}{l}\n\\(x\\)\\\\\n\\end{tabular}"
 	  (orgtbl-to-latex (org-table-to-lisp "| $x$ |") nil)))
   ;; Test pseudo objects and :raw parameter.
   (should

testing/lisp/test-ox-latex.el

@@ -71,14 +71,14 @@ lorem ipsum dolor
     (should
      (search-forward
       "\\begin{verse}
-lorem ipsum dolor\\\\[0pt]
+lorem ipsum dolor\\\\
 lorem ipsum dolor
 
-lorem ipsum dolor\\\\[0pt]
+lorem ipsum dolor\\\\
 lorem ipsum dolor
 
-lorem ipsum dolor\\\\[0pt]
-lorem ipsum dolor\\\\[0pt]
+lorem ipsum dolor\\\\
+lorem ipsum dolor\\\\
 \\end{verse}"))))
 
 (ert-deftest test-ox-latex/longtable ()
@@ -98,15 +98,15 @@ lorem ipsum dolor\\\\[0pt]
     (should
      (search-forward
       "\\begin{longtable}{lr}
-First & Second\\\\[0pt]
-Column & Column\\\\[0pt]
+First & Second\\\\
+Column & Column\\\\
 \\hline
 \\endfirsthead"))
     (goto-char (point-min))
     (should
      (search-forward
-      "First & Second\\\\[0pt]
-Column & Column \\\\[0pt]
+      "First & Second\\\\
+Column & Column \\\\
 
 \\hline
 \\endhead"))