This change adds the notion of a "workspace directory", which is
basically the set of directories that contains workspace packages. These
are mainly used for replace targets right now. It's a little trickier
than expected because the set of workspace directories can technically
change on any go.mod change.
At first, I wanted DidModifyFiles to report whether there was a change,
but I don't think it's actually that expensive to check on each call
and it complicates the code a bit. I can change it back if you think
it's worth doing.
The parse mod handle changes are because I needed an unlocked way of
parsing the mod file, but I imagine they'll conflict with CL 244769
anyway.
The next CL will be to "promote" replace targets to the level of
workspace packages, meaning we will be able to find references in them.
Change-Id: I5dd58fe29415473496ca6634a94a3134923228dc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/245327
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
383b97c0b5