patchapi-credential.txt: document that helpers field is filled-in automatically

> It was unclear whether the field was to be specified by the user of the
> API.
>
> Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
> ---
>
> A quick grep in Git's source code seems to show that no user of the
> API explicitely modify this "helpers" field (except test-credential.c).

>  Documentation/technical/api-credentials.txt | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/technical/api-credentials.txt b/Documentation/technical/api-credentials.txt
> index 21ca6a2..fc6d2b9 100644
> --- a/Documentation/technical/api-credentials.txt
> +++ b/Documentation/technical/api-credentials.txt
> @@ -46,7 +46,9 @@ Functions
>  	consulting helpers, then asking the user. After this function
>  	returns, the username and password fields of the credential are
>  	guaranteed to be non-NULL. If an error occurs, the function will
> -	die().
> +	die(). The `helpers` member of the structure is filled-in
> +	according to the corresponding configuration variables before
> +	consulting helpers.
>  
>  `credential_reject`::

> It was unclear whether the field was to be specified by the user of the
> API.
> 
> Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
> ---
> > It is correct that the C API asks helpers that the user configured,
> > but I think it is common across three API functions, not limited to
> > credential_fill().  credential_apply_config() is called from approve
> > and reject, too.
> 
> Ah, right, so compared to v1, we can move the sentence to the
> description of the "helpers" field, like this:

> diff --git a/Documentation/technical/api-credentials.txt b/Documentation/technical/api-credentials.txt
> index 21ca6a2..48f51ed 100644
> --- a/Documentation/technical/api-credentials.txt
> +++ b/Documentation/technical/api-credentials.txt
> @@ -21,7 +21,9 @@ Data Structures
>  The `helpers` member of the struct is a `string_list` of helpers.  Each
>  string specifies an external helper which will be run, in order, to
>  either acquire or store credentials. See the section on credential
> -helpers below.
> +helpers below. This list is filled-in by the API functions
> +according to the corresponding configuration variables before
> +consulting helpers.

> On Mon, Jun 11, 2012 at 07:51:47PM +0200, Matthieu Moy wrote:
>
>> It was unclear whether the field was to be specified by the user of the
>> API.
>> 
>> Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
>> ---
>> > It is correct that the C API asks helpers that the user configured,
>> > but I think it is common across three API functions, not limited to
>> > credential_fill().  credential_apply_config() is called from approve
>> > and reject, too.
>> 
>> Ah, right, so compared to v1, we can move the sentence to the
>> description of the "helpers" field, like this:
>
> I think this is OK. Technically it loads other matching config, as well
> (filling in default username fields and respecting useHttpPath). I don't
> know if it is worth mentioning them, too.

>> -helpers below.
>> +helpers below. This list is filled-in by the API functions
>> +according to the corresponding configuration variables before
>> +consulting helpers.
>
> You might want to say something like "...and therefore there is usually
> no need for a caller to modify the helpers field at all".