cmd/go: 'go get -d' in a lazy module should promote transitive imports of the named package(s) to roots

[bcmills]

(This is a pre-release cleanup needed for #36460, noticed during testing.)

In go 1.17 modules, we maintain the invariant that the modules providing all packages transitively imported by the main module are listed explicitly in its go.mod file.

go get currently adds a requirement on the module(s) providing the package(s) requested on the command line, but not their transitive imports. (This matches the behavior of go get in pre-1.17 modules.)

However, I expect that most users who run go get on a package will intend to actually import that package. If that is the case, then if they are in the default -mod=readonly mode their builds involving that package will fail until they run go mod tidy.

I would rather that go get make the requested package importable right away, with go mod tidy only needed to clean up any extraneous dependencies afterward. To make that work for go 1.17 modules, go get should be changed to add explicit requirements for all of the indirectly-imported packages too.

CC @jayconrod @matloob

[dmitshur]

@bcmills Checking in from a release meeting as this a release blocking issue, are there updates on this? Thanks.

[bcmills]

I'm still planning to do this. Honestly, I'm not sure that it even needs to block the beta — go get doesn't get a whole lot of user testing anyway, and following it with go mod tidy is fine as a workaround.

[gopherbot]

Change https://golang.org/cl/328231 mentions this issue: cmd/go: in lazy modules, add transitive imports for 'go get' arguments

[gopherbot]

Change https://golang.org/cl/328230 mentions this issue: cmd/go: add a regression test for #45979

[bcmills]

go get in a go 1.17 module now pulls in the transitive dependencies of its arguments, but perhaps it should also fix up the direct/indirect split as well. (Currently it marks even its arguments as indirect, which puts the new dependencies in a separate section due to #45965.) Leaving open for now while we (actively) consider what that behavior should be.