protect call inside Rcpp::Environment<>::namespace_env()

[romainfrancois]

The result of Rf_lang2() is not protected so might be deleted by a garbage collection further down the line.

[kevinushey]

LGTM!

It looks like there are a number of places where we fail to protect the created call, so we might want to audit all of those usages and try to fix them up.

[eddelbuettel]

Quick ag search for Rf_lang2 in the headers find most uses protected by now. Besides the one identified here, I see one more in generated/Function__opearator.h and one in r_cast.h.

Environment.h has another related use with Rf_lang3 and one with Rf_lang4; both probably also need protection.

[kevinushey]

There are also a couple cases where we use Rf_mkString() within calls to Rf_lang*(); IIRC this can be dangerous because (depending on the order the compiler decides to materialize function arguments) this can lead to (very rare) GC errors as well.

We should likely pull those out and protect those as well.

[eddelbuettel]

We could split those two tasks between us :)

[eddelbuettel]

No 'change to worse' in reverse depends: RcppCore/rcpp-logs@d855acb so merging.