PKGMAN_DownloadURL mixes stdout and stderr

[lgoettgens]

When during the download of a file something gets written to stderr by the downloading program, the current implementation interleaves the two outputs, i.e. the error message appears somewhere inside the file. This leads to unexpected behavior when parsing the contents.
This is currently happening as wget 1.21.2 prints SSL_INIT to stderr at the beginning of each download (cf. wget mailing list).

The easy solution would be to remove the interleaving behavior in

PackageManager/gap/PackageManager.gi

Line 935 in d628e84

fullcmd := Concatenation(fullcmd, " ", args, " 2>&1");

However, this is currently the only way to extract stderr from Process (cf. gap-system/gap#4657).

[mtorpey]

Thanks for suggesting this! It may be a good idea to un-interleave these, but I'm not sure what we would then do with the stderr output. Perhaps writing to two different logs would be useful, but I'm not sure. Open to suggestions! :)

[lgoettgens]

Right now, it doesn't get written to any files at all, so your idea doesn't work that easily, as everything is handled by a Process instance. The easiest way, in my opinion, would be to add that feature (keep both stdout and stderr) there and then use it here. Then, interleaving would no longer be needed.
This has already been proposed in gap-system/gap#4657

[mtorpey]

Ah, I see! Sounds good to me – we can wait for the corresponding changes in GAP.

[mtorpey]

I believe this is captured by #104.