cmd/go: module downloads contain vendor/modules.txt

[rsc]

go mod download -json github.com/go-delve/delve@latest
shows a Dir that contains vendor/modules.txt.
None of the other vendor files are present, just modules.txt.

This is probably a bug: we intended for modules to contain
no vendored info at all, but we had to leave files in the root
alone because they might be for a package or command
named vendor (only subdirectories are trimmed).

We should probably update the logic to trim modules.txt
as well, but only when the go.mod has a new enough Go version.

/cc @bcmills

[bcmills]

I think this is another symptom of the known bug described in #31562.

I agree that this is something we can probably fix now that Go 1.21 and above refuse to produce module zips for Go versions that are too new.

[gopherbot]

Change https://go.dev/cl/584635 mentions this issue: x/mod: remove vendor/modules.txt from module download

[gopherbot]

Change https://go.dev/cl/605796 mentions this issue: go.mod: update required go version to go1.22