From 35e087fe5b54b869f5dbbafe8bd0282e16db76c9 Mon Sep 17 00:00:00 2001
From: James Bardin <j.bardin@gmail.com>
Date: Fri, 3 May 2019 16:40:02 -0400
Subject: [PATCH] always re-read datasource if there are dep changes

If a datasource's dependencies have planned changes, then we need to
plan a read for the data source, because the config may change once the
dependencies have been applied.
---
 terraform/node_resource_plan_instance.go | 27 ++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/terraform/node_resource_plan_instance.go b/terraform/node_resource_plan_instance.go
index d69472f82..75e0bcd34 100644
--- a/terraform/node_resource_plan_instance.go
+++ b/terraform/node_resource_plan_instance.go
@@ -81,8 +81,31 @@ func (n *NodePlannableResourceInstance) evalTreeDataResource(addr addrs.AbsResou
 			// here.
 			&EvalIf{
 				If: func(ctx EvalContext) (bool, error) {
-					if state != nil && state.Status != states.ObjectPlanned {
-						return true, EvalEarlyExitError{}
+					depChanges := false
+
+					// Check and see if any of our dependencies have changes.
+					changes := ctx.Changes()
+					for _, d := range n.StateReferences() {
+						ri, ok := d.(addrs.ResourceInstance)
+						if !ok {
+							continue
+						}
+						change := changes.GetResourceInstanceChange(ri.Absolute(ctx.Path()), states.CurrentGen)
+						if change != nil && change.Action != plans.NoOp {
+							depChanges = true
+							break
+						}
+					}
+
+					refreshed := state != nil && state.Status != states.ObjectPlanned
+
+					// If there are no dependency changes, and it's not a forced
+					// read because we there was no Refresh, then we don't need
+					// to re-read. If any dependencies have changes, it means
+					// our config may also have changes and we need to Read the
+					// data source again.
+					if !depChanges && refreshed {
+						return false, EvalEarlyExitError{}
 					}
 					return true, nil
 				},