[GRASS-dev] SEARCH_PATH: current mapset name laundering

[Markus Neteler]

On Mon, May 2, 2011 at 7:05 PM, Glynn Clements <glynn at gclements.plus.com> wrote:
>
> Markus Neteler wrote:
>
>> I sometimes need to rename mapsets and regularly run into the trap that
>> also the first row in the SEARCH_PATH files needs to be updated accordingly.
>> Since I tend to forget about this, maps in the current mapset are no longer
>> found and obscure errors pop up.
>>
>> Questions:
>> - why does the current mapset needs to be specified at all in SEARCH_PATH?
>
> It doesn't "need" to be specified. You can have a search path which
> doesn't include the current mapset.

That's right (but rarely used).

> However, this configuration will break many scripts, which tend to
> assume that a map created by a previous command will be accessible via
> its unqualified name.
>
> Note that similar problems can occur if other mapsets are ahead of the
> current mapset, as an unqualified name refers to the first map found
> in the search path, not necessarily the one in the current mapset.

... in fact, it will be mostly asking for troubles.

>> - wouldn't it be better to auto-add the current mapset name internally?
>> - otherwise, could a test be added upon startup of GRASS to auto-add
>>    the current mapset name is missing from SEARCH_PATH?
>
> Realistically, I think that the current mapset must always be at the
> head of the search path. Allowing it to be otherwise will be
> error-prone.
>
> Otherwise, we have to fix existing scripts to explicitly add the
> current mapset to any temporary map names. It's much simpler to change
> the library to match existing practice.

Definitely - I'd vote for a library update.

> Currently, g.mapsets adds the current mapset to the front of the
> search path if it isn't already present.

Yes, but this helps only if you call g.mapsets which is not necessarily
the case.

> In libgis, if SEARCH_PATH doesn't exist, a default path is created
> containing the current mapset followed by PERMANENT. If SEARCH_PATH
> does exist, it is used verbatim; the current mapset won't be searched
> if it isn't in SEARCH_PATH.

.. which was the trap I met too often in the past.

Markus