append dependencies during refresh

Refresh should load any new dependencies found because of configuration
or state changes, but retain any dependencies already in the state.
Orphaned resources would not be in config, but we do not want to lose
the destroy ordering for the later apply.

terraform/context_refresh_test.go

@@ -1992,6 +1992,17 @@ func TestRefresh_updateDependencies(t *testing.T) {
 		&states.ResourceInstanceObjectSrc{
 			Status:    states.ObjectReady,
 			AttrsJSON: []byte(`{"id":"bar","foo":"foo"}`),
+			Dependencies: []addrs.AbsResource{
+				// Existing dependencies should not be removed during refresh
+				{
+					Module: addrs.RootModuleInstance,
+					Resource: addrs.Resource{
+						Mode: addrs.ManagedResourceMode,
+						Type: "aws_instance",
+						Name: "baz",
+					},
+				},
+			},
 		},
 		addrs.ProviderConfig{
 			Type: "aws",
@@ -2034,6 +2045,7 @@ aws_instance.bar:
   foo = foo
 
   Dependencies:
+    aws_instance.baz
     aws_instance.foo
 aws_instance.foo:
   ID = foo

terraform/eval_refresh.go

@@ -89,6 +89,7 @@ func (n *EvalRefresh) Eval(ctx EvalContext) (interface{}, error) {
 	newState := state.DeepCopy()
 	newState.Value = resp.NewState
 	newState.Private = resp.Private
+	newState.Dependencies = state.Dependencies
 
 	// Call post-refresh hook
 	err = ctx.Hook(func(h Hook) (HookAction, error) {

terraform/eval_state.go

@@ -3,6 +3,7 @@ package terraform
 import (
 	"fmt"
 	"log"
+	"sort"
 
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs"
@@ -203,7 +204,7 @@ type EvalWriteState struct {
 
 	// Dependencies are the inter-resource dependencies to be stored in the
 	// state.
-	Dependencies []addrs.AbsResource
+	Dependencies *[]addrs.AbsResource
 }
 
 func (n *EvalWriteState) Eval(ctx EvalContext) (interface{}, error) {
@@ -228,7 +229,10 @@ func (n *EvalWriteState) Eval(ctx EvalContext) (interface{}, error) {
 	}
 
 	// store the new deps in the state
-	obj.Dependencies = n.Dependencies
+	if n.Dependencies != nil {
+		log.Printf("[TRACE] EvalWriteState: recording %d dependencies for %s", len(*n.Dependencies), absAddr)
+		obj.Dependencies = *n.Dependencies
+	}
 
 	if n.ProviderSchema == nil || *n.ProviderSchema == nil {
 		// Should never happen, unless our state object is nil
@@ -480,3 +484,44 @@ func (n *EvalForgetResourceState) Eval(ctx EvalContext) (interface{}, error) {
 
 	return nil, nil
 }
+
+// EvalRefreshDependencies is an EvalNode implementation that appends any newly
+// found dependencies to those saved in the state. The existing dependencies
+// are retained, as they may be missing from the config, and will be required
+// for the updates and destroys during the next apply.
+type EvalRefreshDependencies struct {
+	// Prior State
+	State **states.ResourceInstanceObject
+	// Dependencies to write to the new state
+	Dependencies *[]addrs.AbsResource
+}
+
+func (n *EvalRefreshDependencies) Eval(ctx EvalContext) (interface{}, error) {
+	state := *n.State
+	if state == nil {
+		// no existing state to append
+		return nil, nil
+	}
+
+	depMap := make(map[string]addrs.AbsResource)
+	for _, d := range *n.Dependencies {
+		depMap[d.String()] = d
+	}
+
+	for _, d := range state.Dependencies {
+		depMap[d.String()] = d
+	}
+
+	deps := make([]addrs.AbsResource, 0, len(depMap))
+	for _, d := range depMap {
+		deps = append(deps, d)
+	}
+
+	sort.Slice(deps, func(i, j int) bool {
+		return deps[i].String() < deps[j].String()
+	})
+
+	*n.Dependencies = deps
+
+	return nil, nil
+}

terraform/node_resource_apply_instance.go

@@ -367,7 +367,7 @@ func (n *NodeApplyableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 				ProviderAddr:   n.ResolvedProvider,
 				ProviderSchema: &providerSchema,
 				State:          &state,
-				Dependencies:   n.Dependencies,
+				Dependencies:   &n.Dependencies,
 			},
 			&EvalApplyProvisioners{
 				Addr:           addr.Resource,
@@ -389,7 +389,7 @@ func (n *NodeApplyableResourceInstance) evalTreeManagedResource(addr addrs.AbsRe
 				ProviderAddr:   n.ResolvedProvider,
 				ProviderSchema: &providerSchema,
 				State:          &state,
-				Dependencies:   n.Dependencies,
+				Dependencies:   &n.Dependencies,
 			},
 			&EvalIf{
 				If: func(ctx EvalContext) (bool, error) {

terraform/node_resource_refresh.go

@@ -214,6 +214,11 @@ func (n *NodeRefreshableManagedResourceInstance) evalTreeManagedResource() EvalN
 				Output: &state,
 			},
 
+			&EvalRefreshDependencies{
+				State:        &state,
+				Dependencies: &n.Dependencies,
+			},
+
 			&EvalRefresh{
 				Addr:           addr.Resource,
 				ProviderAddr:   n.ResolvedProvider,
@@ -228,6 +233,7 @@ func (n *NodeRefreshableManagedResourceInstance) evalTreeManagedResource() EvalN
 				ProviderAddr:   n.ResolvedProvider,
 				ProviderSchema: &providerSchema,
 				State:          &state,
+				Dependencies:   &n.Dependencies,
 			},
 		},
 	}
@@ -287,6 +293,7 @@ func (n *NodeRefreshableManagedResourceInstance) evalTreeManagedResourceNoState(
 				ProviderAddr:   n.ResolvedProvider,
 				ProviderSchema: &providerSchema,
 				State:          &state,
+				Dependencies:   &n.Dependencies,
 			},
 
 			// We must also save the planned change, so that expressions in