Ugg — that's ugly, and quite obfuscated: it isn't apparent from glancing at that code exactly what it does or that it's written like that to avoid a warning

I disagree. That's a common idiomatic way of resolving the problem of false/undef in some expressions and I see it in lots of code.

The only problem with this strategy is that it sometimes gets used in places where non-undef false values like '0' shouldn't be ignored, which can lead to odd bugs. Not a problem in this instance.

$x && reftype $x eq 'HASH'

As already pointed out this breaks for true non-reference values.

In this particular instance I'd probably make it a bit more explicit the exact thing I'm looking for:

# I want a reference whose type is 'HASH'
ref $x && reftype $x eq 'HASH';
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