Make postgis non-relocateable and schema qualify at least core functions

[robe]

I misunderstood the docs a bit. I blame pgAdmin for my stupidity because it always greyed out the schema feature in extension gui if an extension is marked non-relocatable.

I did some experiments, and it does seem that we can schema qualify our functions, without forcing users to install postgis in postgis schema. Though I still think that is where we want to move for the sake of other extensions that may rely on postgis.

Sooo if we have our control file look like this:

# postgis extension
comment = 'PostGIS geometry, geography, and raster spatial types and functions'
default_version = '2.3.0dev'
module_pathname = '$libdir/postgis-2.3'
relocatable = false

Then we can use the variable @extschema@ in lieu of the actual schema name. This will still allow users to do:

CREATE EXTENSION postgis SCHEMA whereever_I_damn_want_you_to_be;

And if I then have ST_Intersects rewritten as:

CREATE OR REPLACE FUNCTION ST_Intersects(geom1 geometry, geom2 geometry)
	RETURNS boolean
	AS 'SELECT $1 && $2 AND @extschema@._ST_Intersects($1,$2)'
	LANGUAGE 'sql' IMMUTABLE;

Once installed, in the desired user location, it will then become:

CREATE OR REPLACE FUNCTION ST_Intersects(geom1 geometry, geom2 geometry)
	RETURNS boolean
	AS 'SELECT $1 && $2 AND whereever_I_damn_want_you_to_be._ST_Intersects($1,$2)'
	LANGUAGE 'sql' IMMUTABLE;

upon installation. The downside being, the user can't then do:

ALTER EXTENSION postgis SET schema public;

They'll get a

ERROR:  extension "postgis" does not support SET SCHEMA

Now how to make this work nicely with non-extension piece.

I have some thoughts.

1) Have all our schema qualified calls have @extschema@ to follow extension convention.

2) Have a build-time extension schema value that defaults to nothing

3) Instead of having the perl build script run once and get used for both extension and non-extension, it would be changed to run twice.

4) If no extension schema is provided (and it's a regular non-extension build run), the perl scripts will just wipe out @extschema@. If there is a build time specified it will replace @extschema@ with the build time version.

5) the the control files, if there is a build-time schema specified (it will put this in the generated control file) — this is more for future.