From aea6b0a7e19414713a47ed12542a26318a7453aa Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Thu, 12 Feb 2015 19:48:57 -0800
Subject: [PATCH] terraform: compare bad diffs for apply

---
 terraform/context_test.go       |  1 -
 terraform/eval_diff.go          | 45 ++++++++++++++++++++++++++++++---
 terraform/transform_resource.go | 26 ++++++++++++++++---
 3 files changed, 63 insertions(+), 9 deletions(-)

diff --git a/terraform/context_test.go b/terraform/context_test.go
index 2203a64f6c..b0b350c526 100644
--- a/terraform/context_test.go
+++ b/terraform/context_test.go
@@ -2817,7 +2817,6 @@ func TestContext2Apply_minimal(t *testing.T) {
 	}
 }
 
-/*
 func TestContext2Apply_badDiff(t *testing.T) {
 	m := testModule(t, "apply-good")
 	p := testProvider("aws")
diff --git a/terraform/eval_diff.go b/terraform/eval_diff.go
index 7e95b3ba4d..3ec842567d 100644
--- a/terraform/eval_diff.go
+++ b/terraform/eval_diff.go
@@ -1,5 +1,38 @@
 package terraform
 
+import (
+	"fmt"
+)
+
+// EvalCompareDiff is an EvalNode implementation that compares two diffs
+// and errors if the diffs are not equal.
+type EvalCompareDiff struct {
+	Info     *InstanceInfo
+	One, Two **InstanceDiff
+}
+
+func (n *EvalCompareDiff) Args() ([]EvalNode, []EvalType) {
+	return nil, nil
+}
+
+// TODO: test
+func (n *EvalCompareDiff) Eval(
+	ctx EvalContext, args []interface{}) (interface{}, error) {
+	one, two := *n.One, *n.Two
+
+	if !one.Same(two) {
+		return nil, fmt.Errorf(
+			"%s: diffs didn't match during apply. This is a bug with "+
+				"Terraform and should be reported.", n.Info.Id)
+	}
+
+	return nil, nil
+}
+
+func (n *EvalCompareDiff) Type() EvalType {
+	return EvalTypeNull
+}
+
 // EvalDiff is an EvalNode implementation that does a refresh for
 // a resource.
 type EvalDiff struct {
@@ -84,11 +117,15 @@ func (n *EvalDiff) Eval(
 
 	// Update our output
 	*n.Output = diff
-	*n.OutputState = state
 
-	// Merge our state so that the state is updated with our plan
-	if !diff.Empty() && n.OutputState != nil {
-		*n.OutputState = state.MergeDiff(diff)
+	// Update the state if we care
+	if n.OutputState != nil {
+		*n.OutputState = state
+
+		// Merge our state so that the state is updated with our plan
+		if !diff.Empty() && n.OutputState != nil {
+			*n.OutputState = state.MergeDiff(diff)
+		}
 	}
 
 	return state, nil
diff --git a/terraform/transform_resource.go b/terraform/transform_resource.go
index e490c51e56..ba06d6a471 100644
--- a/terraform/transform_resource.go
+++ b/terraform/transform_resource.go
@@ -98,7 +98,7 @@ func (n *graphNodeExpandedResource) ProvidedBy() []string {
 
 // GraphNodeEvalable impl.
 func (n *graphNodeExpandedResource) EvalTree() EvalNode {
-	var diff *InstanceDiff
+	var diff, diff2 *InstanceDiff
 	var state *InstanceState
 
 	// Build the resource. If we aren't part of a multi-resource, then
@@ -225,14 +225,32 @@ func (n *graphNodeExpandedResource) EvalTree() EvalNode {
 		Ops: []walkOperation{walkApply},
 		Node: &EvalSequence{
 			Nodes: []EvalNode{
-				&EvalGetProvider{
-					Name:   n.ProvidedBy()[0],
-					Output: &provider,
+				// Redo the diff so we can compare outputs
+				&EvalDiff{
+					Info:     info,
+					Config:   interpolateNode,
+					Provider: &EvalGetProvider{Name: n.ProvidedBy()[0]},
+					State:    &EvalReadState{Name: n.stateId()},
+					Output:   &diff2,
 				},
+
+				// Get the saved diff
 				&EvalReadDiff{
 					Name: n.stateId(),
 					Diff: &diff,
 				},
+
+				// Compare the diffs
+				&EvalCompareDiff{
+					Info: info,
+					One:  &diff,
+					Two:  &diff2,
+				},
+
+				&EvalGetProvider{
+					Name:   n.ProvidedBy()[0],
+					Output: &provider,
+				},
 				&EvalReadState{
 					Name:   n.stateId(),
 					Output: &state,