On reflection (especially after noticing how many buildfarm critters have
__builtin_types_compatible_p but not _Static_assert), it seems like we
ought to try a bit harder to make these macros do something everywhere.
The initial cut at it would have been no help to code that is compiled only
on platforms without _Static_assert, for instance; and in any case not all
our contributors do their initial coding on the latest gcc version.
Some googling about static assertions turns up quite a bit of prior art
for making it work in compilers that lack _Static_assert. The method
that seems closest to our needs involves defining a struct with a bit-field
that has negative width if the assertion condition fails. There seems no
reliable way to get the error message string to be output, but throwing a
compile error with a confusing message is better than missing the problem
altogether.
In the same spirit, if we don't have __builtin_types_compatible_p we can at
least insist that the variable have the same width as the type. This won't
catch errors such as "wrong pointer type", but it's far better than
nothing.
In addition to changing the macro definitions, adjust a
compile-time-constant Assert in contrib/hstore to use StaticAssertStmt,
so we can get some buildfarm coverage on whether that macro behaves sanely
or not. There's surely more places that could be converted, but this is
the first one I came across.
There was an incorrect Assert in hstoreValidOldFormat(), which would cause
immediate core dumps when attempting to work with pre-9.0 hstore data,
but of course only in an assert-enabled build.
Also, ghstore_decompress() incorrectly applied DatumGetHStoreP() to a datum
that wasn't actually an hstore, but rather a ghstore (ie, a gist signature
bitstring). That used to be harmless, but could now result in misbehavior
if the hstore format conversion code happened to trigger. In reality,
since ghstore is not marked toastable (and doesn't need to be), this
function is useless anyway; we can lobotomize it down to returning the
passed-in pointer.
Both bugs found by Andrew Gierth, though this isn't exactly his proposed
patch.
Remove the 64K limit on the lengths of keys and values within an hstore.
(This changes the on-disk format, but the old format can still be read.)
Add support for btree/hash opclasses for hstore --- this is not so much
for actual indexing purposes as to allow use of GROUP BY, DISTINCT, etc.
Add various other new functions and operators.
Andrew Gierth
