Re: [HACKERS] Implement targetlist SRFs using ROWS FROM() (wasChanged SRF in targetlist handling)

I wrote:
> I'll try to write something about the SRF-in-CASE issue too.  Seeing
> whether we can document that adequately seems like an important part
> of making the decision about whether we need to block it.

Here's what I came up with:

  This behavior also means that set-returning functions will be evaluated
  even when it might appear that they should be skipped because of a
  conditional-evaluation construct, such as CASE or COALESCE. For example,
  consider

  SELECT x, CASE WHEN x > 0 THEN generate_series(1, 5) ELSE 0 END FROM tab;

  It might seem that this should produce five repetitions of input rows
  that have x > 0, and a single repetition of those that do not; but
  actually it will produce five repetitions of every input row.

So is this too ugly to live, or shall we put up with it?