I'm putting two related bug reports in this issue.

First: the quickfix "Insert Missing Cast" for BC30512 suggests here to insert CType(expr,String). It should instead be suggesting the nicer CStr(expr).

[edit: retrying this with VS2015 RTM, I can still repro the first issue, but can't repro the second...]

Second: if we switch to Option Strict Custom, the compiler is correct to give warning BC42016 instead of error BC30512. Unfortunately the only quickfix offered for BC42016 is #Disable Warning. But it should first offer the same "Insert Missing Cast" quickfix as it does for BC30512.