terraform: diffs with only tainted set are non-empty

Fixes issue where a resource marked as tainted with no other attribute
diffs would never show up in the plan or apply as needing to be
replaced.

One unrelated test needed updating due to a quirk in the testDiffFn
logic - it adds a "type" field diff if the diff is non-Empty. NBD

helper/schema/schema_test.go

@@ -2400,6 +2400,26 @@ func TestSchemaMap_Diff(t *testing.T) {
 
 			Err: false,
 		},
+
+		"tainted in state w/ no attr changes is still a replacement": {
+			Schema: map[string]*Schema{},
+
+			State: &terraform.InstanceState{
+				Attributes: map[string]string{
+					"id": "someid",
+				},
+				Tainted: true,
+			},
+
+			Config: map[string]interface{}{},
+
+			Diff: &terraform.InstanceDiff{
+				Attributes:     map[string]*terraform.ResourceAttrDiff{},
+				DestroyTainted: true,
+			},
+
+			Err: false,
+		},
 	}
 
 	for tn, tc := range cases {

terraform/context_plan_test.go

@@ -1949,6 +1949,7 @@ func TestContext2Plan_taintDestroyInterpolatedCountRace(t *testing.T) {
 DIFF:
 
 DESTROY/CREATE: aws_instance.foo.0
+  type: "" => "aws_instance"
 
 STATE:
 
@@ -1960,7 +1961,7 @@ aws_instance.foo.2:
   ID = bar
 		`)
 		if actual != expected {
-			t.Fatalf("bad:\n%s", actual)
+			t.Fatalf("[%d] bad:\n%s\nexpected:\n%s\n", i, actual, expected)
 		}
 	}
 }

terraform/diff.go

@@ -361,7 +361,7 @@ func (d *InstanceDiff) Empty() bool {
 
 	d.mu.Lock()
 	defer d.mu.Unlock()
-	return !d.Destroy && len(d.Attributes) == 0
+	return !d.Destroy && !d.DestroyTainted && len(d.Attributes) == 0
 }
 
 func (d *InstanceDiff) GoString() string {

terraform/diff_test.go

@@ -27,6 +27,19 @@ func TestDiffEmpty(t *testing.T) {
 	}
 }
 
+func TestDiffEmpty_taintedIsNotEmpty(t *testing.T) {
+	diff := new(Diff)
+
+	mod := diff.AddModule(rootModulePath)
+	mod.Resources["nodeA"] = &InstanceDiff{
+		DestroyTainted: true,
+	}
+
+	if diff.Empty() {
+		t.Fatal("should not be empty, since DestroyTainted was set")
+	}
+}
+
 func TestModuleDiff_ChangeType(t *testing.T) {
 	cases := []struct {
 		Diff   *ModuleDiff