From add1314195b193f04164cebe558d7a185b61de96 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Sun, 11 Oct 2020 18:28:39 +0200
Subject: [PATCH] Calc: revert to old precedence of '/' in (La)TeX input mode

Make the '/' precedence higher than that of '+' and '-' again,
partially reverting fda9b316f84 (bug#43902).

* lisp/calc/calc-lang.el (tex): Change precedence of '/'.
* test/lisp/calc/calc-tests.el (calc-latex-input): New test.
---
 lisp/calc/calc-lang.el       |  2 +-
 test/lisp/calc/calc-tests.el | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/lisp/calc/calc-lang.el b/lisp/calc/calc-lang.el
index 1c270cfc243..bde5abe649f 100644
--- a/lisp/calc/calc-lang.el
+++ b/lisp/calc/calc-lang.el
@@ -468,10 +468,10 @@
      ( "\\times"  *		   191 190 )
      ( "*"        *		   191 190 )
      ( "2x"	  *		   191 190 )
+     ( "/"	  /		   185 186 )
      ( "+"	  +		   180 181 )
      ( "-"	  -		   180 181 )
      ( "\\over"	  /		   170 171 )
-     ( "/"	  /		   170 171 )
      ( "\\choose" calcFunc-choose  170 171 )
      ( "\\mod"	  %		   170 171 )
      ( "<"	  calcFunc-lt	   160 161 )
diff --git a/test/lisp/calc/calc-tests.el b/test/lisp/calc/calc-tests.el
index d08a1f605b8..fd161027a96 100644
--- a/test/lisp/calc/calc-tests.el
+++ b/test/lisp/calc/calc-tests.el
@@ -636,6 +636,25 @@ An existing calc stack is reused, otherwise a new one is created."
         (should (equal (calcFunc-rot x n w)
                        (calc-tests--rot x n w)))))))
 
+(ert-deftest calc-latex-input ()
+  ;; Check precedence of "/" in LaTeX input mode.
+  (should (equal (math-read-exprs "a+b/c*d")
+                 '((+ (var a var-a) (/ (var b var-b)
+                                       (* (var c var-c) (var d var-d)))))))
+  (unwind-protect
+      (progn
+        (calc-set-language 'latex)
+        (should (equal (math-read-exprs "a+b/c*d")
+                 '((+ (var a var-a) (/ (var b var-b)
+                                       (* (var c var-c) (var d var-d)))))))
+        (should (equal (math-read-exprs "a+b\\over c*d")
+                       '((/ (+ (var a var-a) (var b var-b))
+                            (* (var c var-c) (var d var-d))))))
+        (should (equal (math-read-exprs "a/b/c")
+                       '((/ (/ (var a var-a) (var b var-b))
+                            (var c var-c))))))
+    (calc-set-language nil)))
+
 (provide 'calc-tests)
 ;;; calc-tests.el ends here
 
-- 
2.39.5