Subject: bug#40185: 28.0.50; Emacs Calc selection of a sub-formula doesn't highlight it

From: Narendra Joshi <[email-masked]>
Date: Sun, 22 Mar 2020 19:24:05 +0100

+ Start Emacs Calc with `C-x * *`.
+ Enter the following formula with:
  ' (a + b)^3 / c d
+ Move point to be before "+" and use "j s" to select the 
sub-formula "(a + b)".
+ This should have hidden the rest of the formula. But it does 
not.

           3
    (a + b)
1*  --------
      c d

Selecting a Calc sub-formula doesn't highlight it. For example, in 
the stack entry above, I have selected (a + b) but other parts of 
the formula are still visible. All commands operate on the 
selected formula and it is selected as evident from the '*' after 
the number of the stack entry. It is not highlighted. This seems 
to be working fine in Emacs 26. It's broken in the latest Emacs 
versions: Emacs 27 and Emacs 28. I can confirm that it is not 
happening because of any of my configuration because I tried the 
same thing with `emacs -Q` and the result was the same.

Best, 
-- 
Narendra Joshi