fix(mempkg): don't attempt to validate name of an empty package

[gfanton]

This PR adjusts the behavior of ReadMemPackage. It now skips the package name validation when no gno files are found in the package directory. This modification allows for the utilization of empty parent packages that have a native fallback. For instance, in the foo/bar scenario, where foo is an empty package but has a native implementation defined in imports.go, and bar is a standard package containing gno files. Previously, this would have triggered a panic on foo import due to the empty package name rather than appropriately using the native foo fallback.

While I haven't been able to introduce tests for this change, PR #1066, which incorporates the net/url package, would fail in the absence of this modification due to empty net dependencies.

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[zivkovicmilos]

Looks good 💯

Left a few minor comments

[piux2]

For instance, in the foo/bar scenario, where foo is an empty package but has a native implementation defined in imports.go, and bar is a standard package containing gno files. Previously, this would have triggered a panic on foo import due to the empty package name rather than appropriately using the native foo fallback.

The panic is expected behavior. We do not want to change it.

for foo/bar, only one package node created. pn.Name = bar pn.PkgPath = gnoland/xxx/foo/bar.
No package node is created for foo.

Try to inject native method at foo should should panic in stdlibs/stdlib.go ( for on chain ) and tests/import.go ( for off chain testing).

The native method can only be injected in a valid PackageNode.

Plus:

No need to check memPkg.IsEmpty(), this method is not needed.

Check the reason below

https://github.com/gnolang/gno/pull/1076/files/6ce9a3e72a8158f64ca321738239804356d573ff#r1316600063