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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.
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "gmake all" and "gmake
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.