use interactive shells and bind to work around issue in bash

[FlorianPommerening]

This is a workaround to #502 where environment variables in file names are not completed. The issue is that calling compgen in a nested bash did not recognize the environment variables. It looks like this is a bug that was fixed in bash 5.3 but it still affects earlier versions (https://savannah.gnu.org/support/index.php?111125) For those earlier version, calling bind before the call to compgen forces the necessary initialization.

This works with a normal shell, but produces a warning line editing not enabled because bind is meant for interactive contexts. Using -i to turn the nested shell into an interactive shell avoids the warning. An alternative would be to pipe the warning to /dev/null instead.

[kislyuk]

@FlorianPommerening thanks for digging into this. I like this change and we can call bind as advised by upstream. However I'd like to understand better the possible side effects of starting a bash subprocess with the -i (interactive) option. The bash manual (https://www.gnu.org/software/bash/manual/bash.html#Interactive-Shells) lists a bunch of things that seem like extras that we don't necessarily want.

If the only purpose of -i is to avoid the warning, can we just discard stderr from the shell instead of using -i?

[FlorianPommerening]

Yes, I only added the -i to suppress the warning. As far as I understand, calling bind doesn't make sense in a non-interactive context, so it warns about it. However, we only use bind to initialize some hook that compgen expects, so we can ignore the warning. At least in my tests, it worked fine without -i except for generating the warning.

[kislyuk]

@FlorianPommerening do you want to remove -i or should I? The PR otherwise looks ready to merge.

[FlorianPommerening]

Whatever you prefer but I won't get around to it this week.

[FlorianPommerening]

Sorry this took a while to get around to even if it was a small change but I updated the PR now.

[kislyuk]

Thanks for your work on this! Release coming up shortly.