ox-latex: Make sure that [text] is not misinterpreted as LaTeX argument

* lisp/ox-latex.el (org-latex-plain-text): Protect plain text starting
from [.  It might be misinterpreted as optional command argument if
previous exported fragment ends with a command accepting such.
*
testing/lisp/test-ox-latex.el (text-ox-latex/protect-square-brackets):
Add new test.

Link: https://orgmode.org/list/87o7dju9vn.fsf@posteo.net

lisp/ox-latex.el

@@ -3095,6 +3095,15 @@ contextual information."
 		    "\\(?:[ \t]*\\\\\\\\\\)?[ \t]*\n"
                     (concat org-latex-line-break-safe "\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
+    ;; optional argument.
+    (setq output (replace-regexp-in-string
+                  (rx bol (0+ space) (group "["))
+                  "{[}"
+                  output
+                  nil nil 1))
     ;; Return value.
     output))
 

testing/lisp/test-ox-latex.el

@@ -29,6 +29,29 @@
 
 
 
+(ert-deftest text-ox-latex/protect-square-brackets ()
+  "Test [foo] being interpreted as plain text even after LaTeX commands."
+  (org-test-with-exported-text
+      'latex
+      "* This is test
+lorem @@latex:\\pagebreak@@ [ipsum]
+
+#+begin_figure
+[lorem] figure
+#+end_figure
+
+| [foo] | 2 |
+| [bar] | 3 |
+
+- [bax]
+- [aur]
+"
+    (goto-char (point-min))
+    (should (search-forward "lorem \\pagebreak {[}ipsum]"))
+    (should (search-forward "{[}lorem] figure"))
+    (should (search-forward "{[}foo]"))
+    (should (search-forward "\\item {[}bax]"))))
+
 (ert-deftest test-ox-latex/verse ()
   "Test verse blocks."
   (org-test-with-exported-text