decode change values with marks

Marks stored in a plans.ChangeSrc were not decoded along with the
stored values. This was working in many cases by evaluation correctly
re-evaluating the marks, but this cannot happen in all cases.

plans/changes_src.go

@@ -200,9 +200,10 @@ func (cs *ChangeSrc) Decode(ty cty.Type) (*Change, error) {
 			return nil, fmt.Errorf("error decoding 'after' value: %s", err)
 		}
 	}
+
 	return &Change{
 		Action: cs.Action,
-		Before: before,
+		Before: before.MarkWithPaths(cs.BeforeValMarks),
-		After:  after,
+		After:  after.MarkWithPaths(cs.AfterValMarks),
 	}, nil
 }

plans/changes_test.go

@@ -0,0 +1,41 @@
+package plans
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+func TestChangeEncodeSensitive(t *testing.T) {
+	testVals := []cty.Value{
+		cty.ObjectVal(map[string]cty.Value{
+			"ding": cty.StringVal("dong").Mark("sensitive"),
+		}),
+		cty.StringVal("bleep").Mark("bloop"),
+		cty.ListVal([]cty.Value{cty.UnknownVal(cty.String).Mark("sup?")}),
+	}
+
+	for _, v := range testVals {
+		t.Run(fmt.Sprintf("%#v", v), func(t *testing.T) {
+			change := Change{
+				Before: cty.NullVal(v.Type()),
+				After:  v,
+			}
+
+			encoded, err := change.Encode(v.Type())
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			decoded, err := encoded.Decode(v.Type())
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if !v.RawEquals(decoded.After) {
+				t.Fatalf("%#v != %#v\n", decoded.After, v)
+			}
+		})
+	}
+}