[postgis-devel] Autofix and retry for GEOS overlay ops

[Darafei "Komяpa" Praliaskouski]

Hi,

I've been debugging an issue with ST_Subdivide on one of our polygons. It
traced down to issue in GEOS, and as a part of fix I had to replace
ClipByRect with normal Intersection call. When fixing the tests for old
ClipByRect, that specifically tested some invalid geometries it can
process, I came up with this logic:

https://github.com/postgis/postgis/pull/202/files#diff-c3dac68eb856b0a0554707e2ffcfbf17R648

which boils down to "try intersecting, if failed, MakeValid the inputs, try
intersecting, fail if failed".

This does not make process any slower for anybody now, as current case "we
got it done from first attempt" is not prepended by any additional validity
check.

Thinking of hours spent catching some invalid geometry generated by a chain
of different GEOS operations, I think such change would be beneficial for
all overlay operations. In case someone gets not a desired result, they can
go back to checking their inputs with ST_IsValid, and performing a deep
manual fix, but simple issues like bowties will start simply working.

Thoughts?
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