don't ignore partial containers in diffs

Containers (maps, lists, sets) in an InstanceDiff need to be handled in
their entirety.  Unchanged values cannot be filtered out from diffs, as
providers expect attribute containers to be complete.

If a value in ignore_changes maps to a single key in an attribute
container, and there are other changes present, that ignored value must
be included in the diff as well.

terraform/diff.go

@@ -396,11 +396,6 @@ type ResourceAttrDiff struct {
 	Type        DiffAttrType
 }
 
-// Modified returns the inequality of Old and New for this attr
-func (d *ResourceAttrDiff) Modified() bool {
-	return d.Old != d.New
-}
-
 // Empty returns true if the diff for this attr is neutral
 func (d *ResourceAttrDiff) Empty() bool {
 	return d.Old == d.New && !d.NewComputed && !d.NewRemoved

terraform/eval_diff.go

@@ -256,13 +256,15 @@ func (n *EvalDiff) processIgnoreChanges(diff *InstanceDiff) error {
 		containers := groupContainers(diff)
 		keep := map[string]bool{}
 		for _, v := range containers {
-			if v.keepDiff() {
+			if v.keepDiff(ignorableAttrKeys) {
 				// At least one key has changes, so list all the sibling keys
-				// to keep in the diff if any values have changed
+				// to keep in the diff
 				for k := range v {
-					if v[k].Modified() {
-						keep[k] = true
-					}
+					keep[k] = true
+					// this key may have been added by the user to ignore, but
+					// if it's a subkey in a container, we need to un-ignore it
+					// to keep the complete containter.
+					delete(ignorableAttrKeys, k)
 				}
 			}
 		}
@@ -294,10 +296,17 @@ func (n *EvalDiff) processIgnoreChanges(diff *InstanceDiff) error {
 // a group of key-*ResourceAttrDiff pairs from the same flatmapped container
 type flatAttrDiff map[string]*ResourceAttrDiff
 
-// we need to keep all keys if any of them have a diff
-func (f flatAttrDiff) keepDiff() bool {
-	for _, v := range f {
-		if !v.Empty() && !v.NewComputed {
+// we need to keep all keys if any of them have a diff that's not ignored
+func (f flatAttrDiff) keepDiff(ignoreChanges map[string]bool) bool {
+	for k, v := range f {
+		ignore := false
+		for attr := range ignoreChanges {
+			if strings.HasPrefix(k, attr) {
+				ignore = true
+			}
+		}
+
+		if !v.Empty() && !v.NewComputed && !ignore {
 			return true
 		}
 	}

terraform/eval_diff_test.go

@@ -1,6 +1,7 @@
 package terraform
 
 import (
+	"fmt"
 	"reflect"
 	"testing"
 
@@ -79,7 +80,7 @@ func TestEvalFilterDiff(t *testing.T) {
 	}
 }
 
-func TestProcessIgnoreChangesOnResourceIgnoredWithRequiresNew(t *testing.T) {
+func TestProcessIgnoreChanges(t *testing.T) {
 	var evalDiff *EvalDiff
 	var instanceDiff *InstanceDiff
 
@@ -94,53 +95,84 @@ func TestProcessIgnoreChangesOnResourceIgnoredWithRequiresNew(t *testing.T) {
 			&InstanceDiff{
 				Destroy: true,
 				Attributes: map[string]*ResourceAttrDiff{
+					"resource.%": {
+						Old: "3",
+						New: "3",
+					},
 					"resource.changed": {
 						RequiresNew: true,
 						Type:        DiffAttrInput,
 						Old:         "old",
 						New:         "new",
 					},
-					"resource.unchanged": {
-						Old: "unchanged",
+					"resource.maybe": {
+						Old: "",
 						New: newAttribute,
 					},
+					"resource.same": {
+						Old: "same",
+						New: "same",
+					},
 				},
 			}
 	}
 
-	evalDiff, instanceDiff = testDiffs([]string{"resource.changed"}, "unchanged")
-	err := evalDiff.processIgnoreChanges(instanceDiff)
-	if err != nil {
-		t.Fatalf("err: %s", err)
-	}
-	if len(instanceDiff.Attributes) > 0 {
-		t.Fatalf("Expected all resources to be ignored, found %d", len(instanceDiff.Attributes))
-	}
-
-	evalDiff, instanceDiff = testDiffs([]string{}, "unchanged")
-	err = evalDiff.processIgnoreChanges(instanceDiff)
-	if err != nil {
-		t.Fatalf("err: %s", err)
-	}
-	if len(instanceDiff.Attributes) != 2 {
-		t.Fatalf("Expected 2 resources to be found, found %d", len(instanceDiff.Attributes))
-	}
-
-	evalDiff, instanceDiff = testDiffs([]string{"resource.changed"}, "changed")
-	err = evalDiff.processIgnoreChanges(instanceDiff)
-	if err != nil {
-		t.Fatalf("err: %s", err)
-	}
-	if len(instanceDiff.Attributes) != 1 {
-		t.Fatalf("Expected 1 resource to be found, found %d", len(instanceDiff.Attributes))
-	}
-
-	evalDiff, instanceDiff = testDiffs([]string{}, "changed")
-	err = evalDiff.processIgnoreChanges(instanceDiff)
-	if err != nil {
-		t.Fatalf("err: %s", err)
-	}
-	if len(instanceDiff.Attributes) != 2 {
-		t.Fatalf("Expected 2 resource to be found, found %d", len(instanceDiff.Attributes))
+	for i, tc := range []struct {
+		ignore    []string
+		newAttr   string
+		attrDiffs int
+	}{
+		// attr diffs should be all (4), or nothing
+		{
+			ignore:    []string{"resource.changed"},
+			attrDiffs: 0,
+		},
+		{
+			ignore:    []string{"resource.changed"},
+			newAttr:   "new",
+			attrDiffs: 4,
+		},
+		{
+			attrDiffs: 4,
+		},
+		{
+			ignore:    []string{"resource.maybe"},
+			newAttr:   "new",
+			attrDiffs: 4,
+		},
+		{
+			newAttr:   "new",
+			attrDiffs: 4,
+		},
+		{
+			ignore:    []string{"resource"},
+			newAttr:   "new",
+			attrDiffs: 0,
+		},
+		// extra ignored values shouldn't effect the diff
+		{
+			ignore:    []string{"resource.missing", "resource.maybe"},
+			newAttr:   "new",
+			attrDiffs: 4,
+		},
+		// this isn't useful, but make sure it doesn't break
+		{
+			ignore:    []string{"resource.%"},
+			attrDiffs: 4,
+		},
+	} {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			evalDiff, instanceDiff = testDiffs(tc.ignore, tc.newAttr)
+			err := evalDiff.processIgnoreChanges(instanceDiff)
+			if err != nil {
+				t.Fatalf("err: %s", err)
+			}
+			if len(instanceDiff.Attributes) != tc.attrDiffs {
+				t.Errorf("expected %d diffs, found %d", tc.attrDiffs, len(instanceDiff.Attributes))
+				for k, attr := range instanceDiff.Attributes {
+					fmt.Printf("  %s:%#v\n", k, attr)
+				}
+			}
+		})
 	}
 }