Issue in the function hs_expression_info() about hyperscan HOT 2 CLOSED

Thanks for the bug report!

This does indeed look like an inconsistency, and I will look into it.

from hyperscan.

We have investigated this a little further, and we believe that this is a misunderstanding. I have made some changes to the documentation (see c4e2459) to make this clearer.

Essentially, the hs_expression_info() and hs_expression_ext_info() functions are intended to provide information about an expression, not to be used as a lightweight compile function.

The HS_FLAG_ALLOWEMPTY flag has no effect on the output of the function (as it does not change the semantics of the expression itself), so it does not provoke an error just because hs_compile() would reject the expression. HS_FLAG_SOM_LEFTMOST behaves the same way.

We want these functions to be able to provide useful information about a pattern even if it would fail compilation due to an implementability limitation or a resource limit being exceeded.

from hyperscan.