go list loads packages, sometimes with type information; for example via flags like -export. To properly typecheck or build a package, it's necessary to only load the files for a specific GOOS/GOARCH pair. How would this work?

If you want to list all Go files, you should load all Go files within certain directories, not load entire packages. A package doesn't necessarily include all Go files in a directory, by its own definition.

Can't you use the IgnoredGoFiles field for this?

I think I haven't tried it yet because
UseAllFiles bool // use files regardless of +build lines, file names
describes my need, while
IgnoredGoFiles []string // .go source files ignored due to build constraints
is less clear, and probably ignore then de-ignore is too weird for my brain.

Also IgnoredGoFiles seems .go specific, while UseAllFiles is nicely generic.

But if you tell me that's the exact same end-result, sure, I will do it that way.

I think IgnoredGoFiles is what you want. That will contain .go files that would have been in GoFiles had UseAllFiles been set.

I don't think go list can necessarily implement UseAllFiles the same way go/build does in any case. go list loads a dependency graph of packages, and that graph may be significantly altered if build constraints are ignored. For example, you could end up with dependency cycle errors when no dependency cycle exists on any specific platform.

Ok, thanks for the clarification. I'll try this. Hopefully, it won't hit a corner case no one though of yet.