bug#21521: 24.5; pdb default suggested command

[Stefan Kangas <stefan@marxist.se>]

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tags 21521 + patch
thanks

Stefano Pacifico <github@pacifico.cc> writes:

> When executing `M-x pdb`, the default suggested command is `pdb`, but I couldn’t
> find any validation that standard Python distributions consistently install a
> symlink to`pdb.py` in any `bin` directory (as in the case of my system OS X
> 10.10.5).
>
> If the default command were `python -m pdb`, it would seemingly be compatible with more systems.

This makes sense, and "python -m pdb" is also the recommended usage on
most resources I've been able to find.  On the system I'm on now, the
pdb command is missing.

But I think it's nice to user the shorter version when it's available,
so I suggest to use "python -m pdb" only as a fallback.

Please see the attached patch which does that.

Thanks,
Stefan Kangas

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From aedc63d2ac81c98dbc03c41435d0d2ac82a6a87d Mon Sep 17 00:00:00 2001
From: Stefan Kangas <stefankangas@gmail.com>
Date: Thu, 11 Jul 2019 05:51:18 +0200
Subject: [PATCH] Use "python -m pdb" when "pdb" is missing in M-x pdb

* lisp/progmodes/gud.el (gud-pdb-command-name): Use "python -m pdb"
when the "pdb" command is missing.  (Bug#21521)
---
 lisp/progmodes/gud.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/progmodes/gud.el b/lisp/progmodes/gud.el
index 6b152b7b90..a567508416 100644
--- a/lisp/progmodes/gud.el
+++ b/lisp/progmodes/gud.el
@@ -1673,7 +1673,8 @@ gud-pdb-marker-filter
 
     output))
 
-(defcustom gud-pdb-command-name "pdb"
+(defcustom gud-pdb-command-name
+  (if (executable-find "pdb") "pdb" "python -m pdb")
   "File name for executing the Python debugger.
 This should be an executable on your path, or an absolute file name."
   :type 'string
-- 
2.21.0