bug#48681: Patch: Make prettify-symbols-mode work with ruby-mode

[William Denton <wtd@pobox.com>]

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On 27 May 2021, Lars Ingebrigtsen wrote:

> And then later the commented-out ?∧ (etc) stuff was removed, so I'm
> wondering:
>
>> +(defconst ruby--prettify-symbols-alist
>> +  '(("and" . ?∧)
>> +    ("or" . ?∨))
>> +  "Value for `prettify-symbols-alist' in `ruby-mode'.")
>
> Whether this is something that users of symbol prettification would
> appreciate or not.  Since I use neither prettification or write Ruby, I
> have no opinion here.  Perhaps Stefan has?  (Added to the CCs.)

This got me thinking, and I added four more prettifications (see attached patch) 
for &&, ||, <= and >=, which are all very basic.

I just hack on Ruby, but I use it a lot.  I think that anyone writing Ruby in 
Emacs who already has prettify-symbols-mode turned on (and is seeing it work 
with Python, R, Org, etc.) would, when they see this start working, say, "Hey, 
that's nice."

Thanks for looking at the patch.

Cheers,

Bill

--
William Denton
https://www.miskatonic.org/
Librarian, artist and licensed private investigator.

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diff --git a/lisp/progmodes/ruby-mode.el b/lisp/progmodes/ruby-mode.el
index 0c54a1d27a..a48879bfe6 100644
--- a/lisp/progmodes/ruby-mode.el
+++ b/lisp/progmodes/ruby-mode.el
@@ -2421,6 +2421,15 @@ ruby-flymake-auto
    report-fn
    args))
 
+(defconst ruby--prettify-symbols-alist
+  '(("and" . ?∧)
+    ("&&" . ?∧)
+    ("or" . ?∨)
+    ("||" . ?∨)
+    ("<=" . ?≤)
+    (">=" . ?≥))
+  "Value for `prettify-symbols-alist' in `ruby-mode'.")
+
 ;;;###autoload
 (define-derived-mode ruby-mode prog-mode "Ruby"
   "Major mode for editing Ruby code."
@@ -2437,6 +2446,7 @@ ruby-mode
 
   (setq-local font-lock-defaults '((ruby-font-lock-keywords) nil nil
                                    ((?_ . "w"))))
+  (setq-local prettify-symbols-alist ruby--prettify-symbols-alist)
 
   (setq-local syntax-propertize-function #'ruby-syntax-propertize))