readline ARGV: don't try to open '|-' or '-|' and warn

[tonycoz]

This has no effect on in-place editing nor on the <<>> operator.

Fixes #21176

[aquanight]

Variants of |- and -| that include whitespace will still cause a forked popen but will escape the checks added here.

[jkeenan]

Variants of |- and -| that include whitespace will still cause a forked popen but will escape the checks added here.

Is there reason to believe that "Variants of |- and -| that include whitespace" should be valid Perl code?

[jkeenan]

@tonycoz could you convert this into a smokeme branch? Thanks.

[tonycoz]

Changed this to ignore whitespace around the name, and pushed to a smoke-me

[aquanight]

Variants of |- and -| that include whitespace will still cause a forked popen but will escape the checks added here.

Is there reason to believe that "Variants of |- and -| that include whitespace" should be valid Perl code?

I've checked that such variants are accepted by core open and therefore by <> as well. Whitespace is allowed before, after, and inside the |- or -| construct. E.g.: open my $fd, " | - "; is valid and is a forked open. As such, it would cause a forked open in <> as well.

[jkeenan]

Changed this to ignore whitespace around the name, and pushed to a smoke-me

The results on the smoke-me branch look good. I don't have a good grasp on the other issues raised in this ticket, so I don't know whether we're ready to merge or not.

[tonycoz]

No, I need to re-work it again.