This adds FS.Path which holds the pre-open path currently only used in
WASI. It also fixes a TODO where we didn't know for sure if the FD
parameter for `path_` functions must always be a pre-open. The TL;DR; is
that usually it is, but it may not be (e.g. in our zig-cc example we can
see any directory FD, not just pre-opens).
Finally, this fixes a bug in our path resolution where we mistook paths
like "foo/foo" for "foo" because we only considered basenames instead of
the full path from the pre-open root.
This also makes pre-open directory lookup lazy because I noticed in
Trivy specifically, this is unnecessary for us to do eagerly, as they
change the FS at runtime per-call. In other words, any value from init
time is invalid later.
Signed-off-by: Adrian Cole <adrian@tetrate.io>
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