bug#19145: 24.4; prettify-symbols-mode inconsistent behavior

[Stefan Monnier]

> Some symbols are sometimes not being treated correctly depending on what
> characters follow. For example, I have the following setup for coding
> Python:

>     (prettify-symbols-mode t)
>     (global-prettify-symbols-mode t)
>     (add-hook 'python-mode-hook
>               (lambda ()
>                 (push '("**2" . ?²) prettify-symbols-alist)
>                 (push '("_x" . ?ᵪ) prettify-symbols-alist)
>                 (push '("delta" . ?δ) prettify-symbols-alist)))

Can you try the patch below and see if it does what you want?


        Stefan


diff --git a/lisp/progmodes/prog-mode.el b/lisp/progmodes/prog-mode.el
index 5037020..475dd32 100644
--- a/lisp/progmodes/prog-mode.el
+++ b/lisp/progmodes/prog-mode.el
@@ -73,11 +73,13 @@ Regexp match data 0 points to the chars."
   ;; Check that the chars should really be composed into a symbol.
   (let* ((start (match-beginning 0))
         (end (match-end 0))
-        (syntaxes (if (eq (char-syntax (char-after start)) ?w)
-                      '(?w ?_) '(?. ?\\)))
+        (syntax-beg (if (eq (char-syntax (char-after start)) ?w)
+                         '(?w ?_) '(?. ?\\)))
+        (syntax-end (if (eq (char-syntax (char-before end)) ?w)
+                         '(?w ?_) '(?. ?\\)))
         match)
-    (if (or (memq (char-syntax (or (char-before start) ?\s)) syntaxes)
-           (memq (char-syntax (or (char-after end) ?\s)) syntaxes)
+    (if (or (memq (char-syntax (or (char-before start) ?\s)) syntax-beg)
+           (memq (char-syntax (or (char-after end) ?\s)) syntax-end)
             ;; syntax-ppss could modify the match data (bug#14595)
             (progn (setq match (match-string 0)) (nth 8 (syntax-ppss))))
        ;; No composition for you.  Let's actually remove any composition