Re: proposal: schema variables

The following review has been posted through the commitfest application:
make installcheck-world: tested, passed
Implements feature: not tested
Spec compliant: not tested
Documentation: not tested

1) There are some errors applying the patch against the current master:

fabrizio(at)macanudo:/d/postgresql (master)
$ git apply /tmp/schema-variables-poc-180429-01-diff
/tmp/schema-variables-poc-180429-01-diff:2305: trailing whitespace.

/tmp/schema-variables-poc-180429-01-diff:2317: indent with spaces.
We can support UPDATE and SELECT commands on variables.
/tmp/schema-variables-poc-180429-01-diff:2319: indent with spaces.
possible syntaxes:
/tmp/schema-variables-poc-180429-01-diff:2321: indent with spaces.
-- there can be a analogy with record functions
/tmp/schema-variables-poc-180429-01-diff:2322: indent with spaces.
SELECT varname;
warning: squelched 14 whitespace errors
warning: 19 lines add whitespace errors.

2) There are some warnings when during build process

schemavar.c:383:18: warning: expression which evaluates to zero treated as a null pointer constant of type 'HeapTuple' (aka 'struct HeapTupleData *')
[-Wnon-literal-null-conversion]
HeapTuple tp = InvalidOid;
^~~~~~~~~~
../../../src/include/postgres_ext.h:36:21: note: expanded from macro 'InvalidOid'
#define InvalidOid ((Oid) 0)
^~~~~~~~~
1 warning generated.
tab-complete.c:1268:21: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
{"VARIABLE", NULL, &Query_for_list_of_variables},
^
tab-complete.c:1268:21: note: (near initialization for ‘words_after_create[48].vquery’)
llvmjit_expr.c: In function ‘llvm_compile_expr’:
llvmjit_expr.c:253:3: warning: enumeration value ‘EEOP_PARAM_SCHEMA_VARIABLE’ not handled in switch [-Wswitch]
switch (opcode)
^