Enable pub serve to work without a packages/ directory

[sethladd]

We believe that if the packages/ directory of symlinks was removed, that pub serve would stop working.

This is a tracking bug to ensure that pub serve works, even if there isn't a packages/ directory.

(this issue is part of "Eliminating symlinks, phase two" dart-lang/sdk#24112)

[nex3]

We believe that if the packages/ directory of symlinks was removed, that pub serve would stop working.

I'm not sure where this is coming from (probably me saying something confusing), but pub serve doesn't rely on symlinks at all, and never has. The server automatically serves requests including /packages/ based on its internal knowledge of the package graph, without any reference to a packages/ directory that may or may not exist on the filesystem.

[sethladd]

Ah, thanks for the clarification! Great to know.

(if there are specific cases where pub will break if there isn't a packages/ dir, can you please point me to those issues so we can track? Thanks!)

[nex3]

Other than pub run (which has since been updated), pub existed purely as a generator of the packages/ directory, not as a consumer, so there aren't any cases where it itself will break if the directory stops being generated. There are plenty of cases where users of pub could break, but that's already being (more or less) tracked by e.g. dart-lang/test#327.

[sethladd]

Thanks @nex3 !