Re: [PATCH v3] Allow aliases that include other aliases

From: Tim Schumacher <timschumi@gmx.de>
Date: Sep 6, 2018, 19:31 UTC
Message-ID: <4f814d67-c384-6d1e-a988-97cc25e32475@gmx.de>
In-Reply-To: <xmqqy3cezcz5.fsf@gitster-ct.c.googlers.com>

On 06.09.18 20:40, Junio C Hamano wrote:

Show 28 quoted lines

> Jeff King <peff@peff.net> writes:
> 
>> On Thu, Sep 06, 2018 at 12:16:58PM +0200, Tim Schumacher wrote:
>>
>>> @@ -691,17 +692,23 @@ static int run_argv(int *argcp, const char ***argv)
>>>   		/* .. then try the external ones */
>>>   		execv_dashed_external(*argv);
>>>   
>>> -		/* It could be an alias -- this works around the insanity
>>> +		if (string_list_has_string(&cmd_list, *argv[0]))
>>> +			die(_("loop alias: %s is called twice"), *argv[0]);
>>
>> I pointed this out in my response to Ævar, but I want to make sure it
>> gets seen. This call assumes the list is sorted, but...
>>
>>> +		string_list_append(&cmd_list, *argv[0]);
>>
>> This will create an unsorted list. You'd have to use
>> string_list_insert() here for a sorted list, or
>> unsorted_string_list_has_string() in the earlier call.
> 
> Correct.
> 
> Also, normal users who have never seen this loop that implements
> alias expansion would not have a clue when they see "called twice".
> 
> I actually think the caller should also pass cmd to run_argv() and
> then we should use it (and not argv[]) in this die() message.

Could we just save the first element of the original argv for that purpose? Or alternatively, use the first stored element in the command list?

Show 14 quoted lines

> When
> the original command was foo that is aliased to bar, which in turn
> is aliased to baz, which in turn is aliased to bar, especially that
> "git foo" invocation was in a random script written six weeks ago by
> the user, it would be a lot more helpful to see
> 
>      "alias loop detected: expansion of 'git foo' does not terminate"
> 
> than
> 
>      "loop alias: bar is called twice".
> 
> given that 'bar' is not something the user called, or written in the
> script she wrote six weeks ago.

Indeed, printing the command that the user called is a better message than the command that is the entry-point of the loop. I'll change it in v4.

Show 23 quoted lines

> 
>> It's unfortunate that string_list makes this so easy to get wrong.
>>
>>> +
>>> +		/*
>>> +		 * It could be an alias -- this works around the insanity
>>>   		 * of overriding "git log" with "git show" by having
>>>   		 * alias.log = show
>>>   		 */
>>> -		if (done_alias)
>>> -			break;
>>>   		if (!handle_alias(argcp, argv))
>>>   			break;
>>> -		done_alias = 1;
>>> +		done_alias++;
>>
>> I don't think anybody cares about done_alias being an accurate count.
>> Should we just leave this as-is?
> 
> Good point.  The only caller treats it as a bool (i.e. "should the
> failure be reported as failure to expand an alias cmd which resulted
> in (updated) argv[0] that is not a git command?").
>

As the string-list has its own counter, I guess the done_alias variable can be reverted to a simple 0/1 value.