cmd/cue: only ignore type and parse errors with get go

Unknown or list-related errors should always be reported back to the
user. Otherwise, it's totally unclear what has gone wrong.

Change-Id: I9241acb100818dc051f852c98df0f94fb6e68c2b
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/8961
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>

cmd/cue/cmd/get_go.go

@@ -399,6 +399,19 @@ func extract(cmd *Command, args []string) error {
 	if err != nil {
 		return err
 	}
+	var errs []string
+	for _, p := range pkgs {
+		for _, e := range p.Errors {
+			switch e.Kind {
+			case packages.ParseError, packages.TypeError:
+			default:
+				errs = append(errs, fmt.Sprintf("\t%s: %v", p.PkgPath, e))
+			}
+		}
+	}
+	if len(errs) > 0 {
+		return fmt.Errorf("could not load Go packages:\n%s", strings.Join(errs, "\n"))
+	}
 
 	e := extractor{
 		cmd:    cmd,

cmd/cue/cmd/testdata/script/get_go_unresolvable_package.txt

@@ -0,0 +1,14 @@
+# Test that we get expected error when we ask cue get go to get
+# a Go package that cannot be resolved.
+
+# Ensure that we don't automatically add the missing dependency pre Go 1.16
+[!go1.16] env GOFLAGS=-mod=readonly
+
+! cue get go k8s.io/api/apps/v1
+[go1.16] stderr '\Qno required module provides package k8s.io/api/apps/v1'
+[go1.14] [!go1.16] stderr '\Qcannot find module providing package k8s.io/api/apps/v1: import lookup disabled by -mod=readonly'
+
+-- go.mod --
+module mod.com/blah
+
+go 1.14