terraform: Diff.Equal and tests

terraform/diff.go

@@ -81,6 +81,25 @@ func (d *Diff) Empty() bool {
 	return true
 }
 
+// Equal compares two diffs for exact equality.
+//
+// This is different from the Same comparison that is supported which
+// checks for operation equality taking into account computed values. Equal
+// instead checks for exact equality.
+func (d *Diff) Equal(d2 *Diff) bool {
+	// If one is nil, they must both be nil
+	if d == nil || d2 == nil {
+		return d == d2
+	}
+
+	// Sort the modules
+	sort.Sort(moduleDiffSort(d.Modules))
+	sort.Sort(moduleDiffSort(d2.Modules))
+
+	// Use DeepEqual
+	return reflect.DeepEqual(d, d2)
+}
+
 // DeepCopy performs a deep copy of all parts of the Diff, making the
 // resulting Diff safe to use without modifying this one.
 func (d *Diff) DeepCopy() *Diff {
@@ -659,3 +678,21 @@ func (d *InstanceDiff) Same(d2 *InstanceDiff) (bool, string) {
 
 	return true, ""
 }
+
+// moduleDiffSort implements sort.Interface to sort module diffs by path.
+type moduleDiffSort []*ModuleDiff
+
+func (s moduleDiffSort) Len() int      { return len(s) }
+func (s moduleDiffSort) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s moduleDiffSort) Less(i, j int) bool {
+	a := s[i]
+	b := s[j]
+
+	// If the lengths are different, then the shorter one always wins
+	if len(a.Path) != len(b.Path) {
+		return len(a.Path) < len(b.Path)
+	}
+
+	// Otherwise, compare lexically
+	return strings.Join(a.Path, ".") < strings.Join(b.Path, ".")
+}

terraform/diff_test.go

@@ -40,6 +40,50 @@ func TestDiffEmpty_taintedIsNotEmpty(t *testing.T) {
 	}
 }
 
+func TestDiffEqual(t *testing.T) {
+	cases := map[string]struct {
+		D1, D2 *Diff
+		Equal  bool
+	}{
+		"nil": {
+			nil,
+			new(Diff),
+			false,
+		},
+
+		"empty": {
+			new(Diff),
+			new(Diff),
+			true,
+		},
+
+		"different module order": {
+			&Diff{
+				Modules: []*ModuleDiff{
+					&ModuleDiff{Path: []string{"root", "foo"}},
+					&ModuleDiff{Path: []string{"root", "bar"}},
+				},
+			},
+			&Diff{
+				Modules: []*ModuleDiff{
+					&ModuleDiff{Path: []string{"root", "bar"}},
+					&ModuleDiff{Path: []string{"root", "foo"}},
+				},
+			},
+			true,
+		},
+	}
+
+	for name, tc := range cases {
+		t.Run(name, func(t *testing.T) {
+			actual := tc.D1.Equal(tc.D2)
+			if actual != tc.Equal {
+				t.Fatalf("expected: %v\n\n%#v\n\n%#v", tc.Equal, tc.D1, tc.D2)
+			}
+		})
+	}
+}
+
 func TestModuleDiff_ChangeType(t *testing.T) {
 	cases := []struct {
 		Diff   *ModuleDiff