In the course of CL 503195 I noticed that minor changes to source files (such as the insertion of a comment) cause re-typechecking (from syntax) of far more packages than one might expect based on the change. This appeared to be the case both before and after the change in that CL.

For example, if I enable this log line:

func (an *analysisNode) typeCheck(parsed []*source.ParsedGoFile) *analysisPackage {
	if true { // debugging
		log.Println("typeCheck", m.ID)
	}

and run go run ./gopls check ./gopls/main.go, I observe:

1. first run: typechecks everything.
2. second run: typechecks nothing.
3. edit gopls/internal/lsp/cmd/cmd.go: add a comment after the import block. run again: type checks a lot of packages, far more than the upward dependencies of the edit. To pick one at random, honnef.co/go/tools/analysis/facts/purity. Yet go list -deps honnef.co/go/tools/analysis/facts/purity | grep gopls is empty, i.e. we re-typechecked a package that does not transitively depend on the changed package.