It would be helpful to add an "-exclude_gopath" flag to godoc command.

Reason

Godoc automatically includes the default Go path value without any apparent option to disable this behaviour. It could be helpful in certain cases to disable this behaviour, for example, when a user wishes just to exam only the official Go standard library documentation and not EVERYTHING they currently have in their source folder. This would be helpful when a user is trying to learn Go by reading the official documentation in an offline mode by using "godoc -http". The current behaviour makes readability quite poor if the user has a large number of packages installed and is primarily interested in only the official documentation.

Currently, the user's $GOPATH environment variable can't even be used to temporarily override this default behaviour, for example:

~$ GOPATH="" godoc -http

This example command line fails because build.Default.GOPATH adds Go's default GOPATH value regardless.

Implementation

Rather than suggest a change to the build context default, I'm proposing that a flag be added to the godoc cmd that enables a user to simply exclude the GOPATH source files from a godoc command session.

The following lines would be added to / changed in main.go:

excludeGopath = flag.Bool("exclude_gopath", false, "exclude packages in $GOPATH")

if !*excludeGoPath {
	// Bind $GOPATH trees into Go root.
	for _, p := range filepath.SplitList(build.Default.GOPATH) {
		fs.Bind("/src", gatefs.New(vfs.OS(p), fsGate), "/src", vfs.BindAfter)
	}
}

This proposal avoids any platform specific issues by simply entirely bypassing the processing of that path. If any future changes were to the underling default context to better support this behaviour it could easily be rolled back.

Note

If this proposed change is accepted then I'd naturally be happy to write it up.