pgsql: Ensure that whole-row junk Vars are always of composite type.

Ensure that whole-row junk Vars are always of composite type.

The EvalPlanQual machinery assumes that whole-row Vars generated for the
outputs of non-table RTEs will be of composite types. However, for the
case where the RTE is a function call returning a scalar type, we were
doing the wrong thing, as a result of sharing code with a parser case
where the function's scalar output is wanted. (Or at least, that's what
that case has done historically; it does seem a bit inconsistent.)

To fix, extend makeWholeRowVar's API so that it can support both use-cases.
This fixes Belinda Cussen's report of crashes during concurrent execution
of UPDATEs involving joins to the result of UNNEST() --- in READ COMMITTED
mode, we'd run the EvalPlanQual machinery after a conflicting row update
commits, and it was expecting to get a HeapTuple not a scalar datum from
the "wholerowN" variable referencing the function RTE.

Back-patch to 9.0 where the current EvalPlanQual implementation appeared.

In 9.1 and up, this patch also fixes failure to attach the correct
collation to the Var generated for a scalar-result case. An example:
regression=# select upper(x.*) from textcat('ab', 'cd') x;
ERROR: could not determine which collation to use for upper() function

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/dd3bab5fd74db009c946278bb314c8458a2fef11

Modified Files
--------------
src/backend/nodes/makefuncs.c | 45 ++++++++++++++++---------------
src/backend/optimizer/prep/preptlist.c | 3 +-
src/backend/parser/parse_expr.c | 11 ++++++-
src/backend/rewrite/rewriteHandler.c | 3 +-
src/include/nodes/makefuncs.h | 3 +-
5 files changed, 38 insertions(+), 27 deletions(-)