Re: Remove redundant initializations

I'm +1 for the $SUBJECT concept, mostly because I take longer to read code
where immaterial zero-initialization lines are diluting the code.  A quick
scan of the patch content is promising.  If there's a decision to move
forward, I'm happy to review it more closely.

On Wed, Jun 30, 2021 at 09:28:17AM -0400, Tom Lane wrote:
> David Rowley <dgrowleyml@gmail.com> writes:
> > On Tue, 29 Jun 2021 at 02:15, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> The primary case where I personally rely on that style is when adding a
> >> new field to a struct.  Currently it's possible to grep for some existing
> >> field and add the new one beside it.  Leaving out initializations by
> >> relying on side-effects of makeNode makes that far riskier.
> 
> > FWIW, I mostly grep for makeNode(NameOfNode) as I'm a bit mistrusting
> > of if the random existing field name that I pick to grep for will
> > properly showing me all the locations I should touch.
> 
> I tend to do that too, but it's not a foolproof thing either, since
> some places use random memset's for the purpose.

I checked the first five matches of "git grep ' = T_'" to get a sense of code
sites that skip makeNode().  Just one of those five initializes every field:

recordDependencyOnSingleRelExpr() builds RangeTblEntry, subset of fields
EventTriggerCommonSetup() builds EventTriggerData, full fields
validateForeignKeyConstraint() builds TriggerData, subset of fields
ExecBSInsertTriggers() builds TriggerData, subset of fields [many similar examples in trigger.c]
ExecBuildProjectionInfo() builds ExprState, subset of fields

Hence, I find we're already too inconsistent about "explicitly initialize
every field" to recommend "grep for some existing field".  (Two participants
in the 2018 thread made similar observations[1][2].)  grepping T_NameOfNode
and then makeNode(NameOfNode) is more reliable today, and $SUBJECT will not
decrease its reliability.

[1] https://postgr.es/m/20180830045736.p3mrugcq2j367a3l@alap3.anarazel.de
[2] https://postgr.es/m/CA+TgmoYPw3Y8ZKofseTpVbb8avy7v7JbjmG6BMe7cC+eOd7qVA@mail.gmail.com