State the arguments a forwarding SQL function passes twice

[estebanzimanyi]

A SQL function with no C symbol whose body forwards its arguments to one
C-backed signature, repeating one of them or passing a literal in place of
one, is a signature of the wrapper behind the signature it calls.
spaceSplit(tgeompoint, xsize, sorigin, bitmatrix, borderInc) is the body
SELECT spaceSplit($1, $2, $2, $2, $3, $4, $5): it is a signature of
Tgeo_space_split, and tgeo_space_split states it with
repeatedArgs: {ysize: xsize, zsize: xsize}, keyed by the C parameter the
repeat fills and valued by the C parameter the first occurrence fills, as
boundArgs keys a literal. stops(tgeompoint, minduration) is
SELECT stops($1, 0.0, $2), stated with boundArgs: {maxdist: 0.0} on its own
signature.

The signature called is the one of that name whose argument count admits
the call, defaults included, and whose argument at each position a $k fills
has the type of argument k, float8 meeting float. The arguments of a
signature fill in order the C parameters that are neither out-parameters nor
bound by the wrapper, so the argument passed at position i fills the i-th of
them. A call two signatures fit, or a function whose inputs do not line up
with the arguments of its signature, stops the catalog. A body computing an
argument, a cast or a call, is a composition and adds no signature.

Why. A binding registers one function per SQL signature and calls MEOS from
the arguments it receives. The forwarding functions are the forms a user
calls with one size for a cubic grid, and the catalog stated none of them:
their CREATE FUNCTION names no C symbol.

Measured. Over MobilityDB 8a23781e4c, 13 functions gain 39 signatures: 32
repeat an argument (spaceSplit, spaceTimeSplit, spaceBoxes, spaceTimeBoxes,
spaceTiles, spaceTimeTiles, getSpaceTile, getSpaceTimeTile), stating 48
repeatedArgs entries, and 7 pass a literal (stops, translate, scale), taking
the bound literals from 1826 to 1833. The sqlArity of 12 of them drops by
the sizes the one- and two-size forms omit. The 16 forwards over tpose and
tpcpoint call a signature that is itself a composition and add none. The
catalog is otherwise identical to the one derived without the change, and
its OpenAPI projection validates.

Witness. tests/test_sqlfn_forward.py reads a repeat and a literal as a
forward and a cast, a call, a reordering, a dropped or an unchanged argument
as none, attaches a forward to the wrapper of the signature it calls through
the type spellings, adds none for a forward calling a composition, stops on
a call two signatures fit and on inputs not lining up, and states
repeatedArgs and the forward's own boundArgs through merge_boundargs. The
suite floor goes from 337 to 352.