And it passed local unit tests...

...
[----------] Global test environment tear-down
[ SKIPSTAT ] 36 tests skipped
[ SKIPSTAT ] TAG='mem_6gb' skip 1 tests
[ SKIPSTAT ] TAG='skip_bigdata' skip 1 tests
[ SKIPSTAT ] TAG='skip_other' skip 34 tests
[==========] 11659 tests from 251 test cases ran. (82892 ms total)
[  PASSED  ] 11659 tests.

The ABI compatibility checker running under linux x64 failed. It is due to the 4 UMat static factory APIs to which I added the usageFlags param. Naturally, the header sets the default so it is API compatible, but at the same time the underlying function signature has widened by one param so it is not ABI compatible. In this scenario, I think this means that recompile and linking to a library would work (as it would have the new header). In constrast, an app that uses (without recompile) a precompiled OpenCV DLL or SO would fail if these 4 APIs were called.

I googled and I did not find an OpenCV doc regarding the topic of ABI compatibility. Is there a doc? If not, would you share OpenCV's approach on this topic? (Might be good to put in Wiki)

Technically, if ABI compatibility is desired while also having these 4 factory updates, I could create sibling APIs. It would double the number of factory APIs. I would simplify when possible, might have the old APIs call the newer wider APIs. Makes the codebase larger and more to maintain -- but that is the cost of maintaining ABI on these...if you want these updates.