Re: split rm_name and rm_desc out of rmgr.c

Tom Lane wrote:

> Couldn't we do something similar to the design for SQL keyword constants,
> wherein the actual data is in macros in a header file (providing exactly
> one source of truth for each RM) and then various .c files can #include
> that after #defining the macro as they need?

Here are two patches implementing this idea.  The first one is simpler
and just replaces the table in rmgr.c with an appropriate PG_RMGR
define.

The second one touches rmgr.h as well.  That file currently has a list
of #defines with symbolic rmgr names and their numeric IDs.  The
approach in the second patch is to turn these into "extern const RmgrId"
instead, and use a second inclusion of rmgrlist.h in rmgr.c that assigns
them the values as consts.  This has the disadvantage that the array
size RM_MAX_ID cannot use the symbolic RM_SPGIST_ID value, but instead
it needs a literal "16".  Otherwise the compile complains:
error: variably modified ‘RmgrTable’ at file scope

I am not too sure about that second change.  However, I'm a bit uneasy
about leaving a second list of rmgrs around; since we're creating what
should be the canonical list of rmgrs, it makes sense to reduce the two
copies we have.  Better ideas for that second list are welcome.

--
Álvaro Herrera                http://www.2ndQuadrant.com/
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