Merge pull request #9618 from hashicorp/b-computed-prim

helper/schema,terraform: handle computed primitives in diffs

helper/schema/schema.go

@@ -995,7 +995,7 @@ func (m schemaMap) diffString(
 	all bool) error {
 	var originalN interface{}
 	var os, ns string
-	o, n, _, _ := d.diffChange(k)
+	o, n, _, computed := d.diffChange(k)
 	if schema.StateFunc != nil && n != nil {
 		originalN = n
 		n = schema.StateFunc(n)
@@ -1019,7 +1019,7 @@ func (m schemaMap) diffString(
 		}
 
 		// Otherwise, only continue if we're computed
-		if !schema.Computed {
+		if !schema.Computed && !computed {
 			return nil
 		}
 	}
@@ -1033,10 +1033,11 @@ func (m schemaMap) diffString(
 	}
 
 	diff.Attributes[k] = schema.finalizeDiff(&terraform.ResourceAttrDiff{
-		Old:        os,
-		New:        ns,
-		NewExtra:   originalN,
-		NewRemoved: removed,
+		Old:         os,
+		New:         ns,
+		NewExtra:    originalN,
+		NewRemoved:  removed,
+		NewComputed: computed,
 	})
 
 	return nil

helper/schema/schema_test.go

@@ -439,8 +439,9 @@ func TestSchemaMap_Diff(t *testing.T) {
 			Diff: &terraform.InstanceDiff{
 				Attributes: map[string]*terraform.ResourceAttrDiff{
 					"availability_zone": &terraform.ResourceAttrDiff{
-						Old: "",
-						New: "${var.foo}",
+						Old:         "",
+						New:         "${var.foo}",
+						NewComputed: true,
 					},
 				},
 			},
@@ -1675,8 +1676,9 @@ func TestSchemaMap_Diff(t *testing.T) {
 						New: "1",
 					},
 					"route.~1.gateway": &terraform.ResourceAttrDiff{
-						Old: "",
-						New: "${var.foo}",
+						Old:         "",
+						New:         "${var.foo}",
+						NewComputed: true,
 					},
 				},
 			},

terraform/diff.go

@@ -611,6 +611,13 @@ func (d *InstanceDiff) Same(d2 *InstanceDiff) (bool, string) {
 				continue
 			}
 
+			// If the last diff was a computed value then the absense of
+			// that value is allowed since it may mean the value ended up
+			// being the same.
+			if diffOld.NewComputed {
+				continue
+			}
+
 			// No exact match, but maybe this is a set containing computed
 			// values. So check if there is an approximate hash in the key
 			// and if so, try to match the key.

terraform/diff_test.go

@@ -567,6 +567,47 @@ func TestInstanceDiffSame(t *testing.T) {
 			"diff RequiresNew; old: true, new: false",
 		},
 
+		// NewComputed on primitive
+		{
+			&InstanceDiff{
+				Attributes: map[string]*ResourceAttrDiff{
+					"foo": &ResourceAttrDiff{
+						Old:         "",
+						New:         "${var.foo}",
+						NewComputed: true,
+					},
+				},
+			},
+			&InstanceDiff{
+				Attributes: map[string]*ResourceAttrDiff{
+					"foo": &ResourceAttrDiff{
+						Old: "0",
+						New: "1",
+					},
+				},
+			},
+			true,
+			"",
+		},
+
+		// NewComputed on primitive, removed
+		{
+			&InstanceDiff{
+				Attributes: map[string]*ResourceAttrDiff{
+					"foo": &ResourceAttrDiff{
+						Old:         "",
+						New:         "${var.foo}",
+						NewComputed: true,
+					},
+				},
+			},
+			&InstanceDiff{
+				Attributes: map[string]*ResourceAttrDiff{},
+			},
+			true,
+			"",
+		},
+
 		{
 			&InstanceDiff{
 				Attributes: map[string]*ResourceAttrDiff{