Advertise only spellable paths, and name what a choice's variants share

edge_test.go

@@ -97,6 +97,7 @@ func TestPathThroughChoice(t *testing.T) {
 	dir := writeData(t, map[string]string{
 		"every":  `[{"format":"{f}","f":["1"]},{"format":"{f}","f":["2"]}]`,
 		"notall": `[{"format":"{f}","f":["1"]},["plain"]]`,
+		"some":   `[{"format":"{f}","f":["1"]},{"format":"{f}","f":["2"],"extra":["x"]}]`,
 	})
 	f := newFakes(t, dir, WithSeed(1))
 	for i := 0; i < 200; i++ {
@@ -104,6 +105,10 @@ func TestPathThroughChoice(t *testing.T) {
 			t.Fatalf("every.f = %q, want 1 or 2", got)
 		}
 	}
+	// A path only some variants carry is reported against what all of them carry.
+	if _, err := f.Fake("some.extra"); err == nil || !strings.Contains(err.Error(), "all carry [f]") {
+		t.Errorf("Fake(some.extra) = %v, want it to name what every variant carries", err)
+	}
 	var first string
 	for i := 0; i < 200; i++ {
 		_, err := f.Fake("notall.f")