So it is scalar context. (Thanks for the correction on wantarray.)

By way of an explanation: I misremembered the issue I had in mind. What I was thinking of is that the scalar reference-taking operator \ evaluates its argument in list context. This came up in discussion of the (ab)use of @{[]} or ${\()} constructs to put code inside here-docs.

Makeshifts last the longest.

$ perl -le'print @{warn wantarray ? 1 : defined wantarray ? 0 : "undef
+"}'
undef at -e line 1.
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Makeshifts last the longest.

You've misused wantarray. It tells the context in which the current subroutine was called, not in what context wantarray was called.

 > perl
sub context {
    warn
        !defined wantarray
            ? "void" :
        wantarray ? "list" : "scalar",
        $/;
}
@{context()};
<EOF>
scalar
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- tye