vbc builds an exception filter as a single non-short-circuiting
expression: `isinst`, then the user's `when` conditions, combined with
`and`. DetectCatchWhenConditionBlocks only knew the branch chain csc
emits, so the type test stayed inside the filter and the handler kept the
`object` variable it has in IL:
catch (object obj) when ((obj is Exception) & (num2 != 0) & (num == 0))
{
ProjectData.SetProjectError((Exception)obj);
A catch type has to derive from Exception, so that does not compile.
The conjunction form is matched too now, lifting the test to the catch
type as the block form already does. The other conjuncts stop running for
a non-matching exception once the test moves, so the filter has to be
pure for this to be invisible; PropagateExceptionVariable then drops the
castclass in the handler:
catch (Exception ex) when ((num2 != 0) & (num == 0))
{
ProjectData.SetProjectError(ex);
Closes#3659
dualfroz
upstream