This is proposal 2 of 3 coming out of the discussion of issue #38234.

We propose adding a pointer to new struct containing module information to the Package struct. This struct might be the Module struct reported by go list, or another struct defined in x/tools/go/packages or somewhere in x/mod.

go/packages was originally conceived as being build-system independent, and not all build systems use modules. But now, even Bazel supports modules, and even if a user isn't using modules for their own build, they need to produce modules for consumers of their libraries. Given how widespread the use of modules is, and how modules can be used across build systems, it seems reasonable to add information about a package's module (if it has one) to its Package struct.

If this proposal were accepted, we'd also need to add a Need bit to request a module, and give users the expectation that module information might not always be present.