terraform: nil out the Diff on a resource when expanding

This fixes a bug where the Destroy diff was being kept around for
nodes that shouldn't be destroyed. We added a test to verify this
doesn't happen.

terraform/context.go

@@ -862,6 +862,8 @@ func (c *walkContext) planWalkFn() depgraph.WalkFunc {
 		}
 
 		if !diff.Empty() {
+			log.Printf("[DEBUG] %s: Diff: %#v", r.Id, diff)
+
 			l.Lock()
 			md := result.Diff.ModuleByPath(c.Path)
 			if md == nil {
@@ -1259,6 +1261,9 @@ func (c *walkContext) genericWalkResource(
 		return err
 	}
 
+	println(fmt.Sprintf("%s NODES: %#v", rn.Resource.Id, ns))
+	println(fmt.Sprintf("%s DIFF: %#v", rn.Resource.Id, rn.Resource.Diff))
+
 	// Go through all the nouns and run them in parallel, collecting
 	// any errors.
 	var l sync.Mutex

terraform/context_test.go

@@ -940,6 +940,132 @@ func TestContextApply_compute(t *testing.T) {
 	}
 }
 
+func TestContextApply_countDecrease(t *testing.T) {
+	m := testModule(t, "apply-count-dec")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	s := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.foo.0": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"foo":  "foo",
+								"type": "aws_instance",
+							},
+						},
+					},
+					"aws_instance.foo.1": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"foo":  "foo",
+								"type": "aws_instance",
+							},
+						},
+					},
+					"aws_instance.foo.2": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"foo":  "foo",
+								"type": "aws_instance",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: s,
+	})
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyCountDecStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s", actual)
+	}
+}
+
+func TestContextApply_countDecreaseToOne(t *testing.T) {
+	m := testModule(t, "apply-count-dec-one")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	s := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.foo.0": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"foo":  "foo",
+								"type": "aws_instance",
+							},
+						},
+					},
+					"aws_instance.foo.1": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+						},
+					},
+					"aws_instance.foo.2": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: s,
+	})
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyCountDecToOneStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s", actual)
+	}
+}
+
 func TestContextApply_module(t *testing.T) {
 	m := testModule(t, "apply-module")
 	p := testProvider("aws")

terraform/graph.go

@@ -1750,6 +1750,7 @@ func (n *GraphNodeResource) copyResource(id string) *Resource {
 	resource.Id = id
 	resource.Info = &info
 	resource.Config = NewResourceConfig(n.Config.RawConfig)
+	resource.Diff = nil
 	return &resource
 }
 

terraform/terraform_test.go

@@ -206,6 +206,24 @@ aws_instance.foo:
   type = aws_instance
 `
 
+const testTerraformApplyCountDecStr = `
+aws_instance.foo.0:
+  ID = bar
+  foo = foo
+  type = aws_instance
+aws_instance.foo.1:
+  ID = bar
+  foo = foo
+  type = aws_instance
+`
+
+const testTerraformApplyCountDecToOneStr = `
+aws_instance.foo.0:
+  ID = bar
+  foo = foo
+  type = aws_instance
+`
+
 const testTerraformApplyMinimalStr = `
 aws_instance.bar:
   ID = foo

terraform/test-fixtures/apply-count-dec-one/main.tf

@@ -0,0 +1,7 @@
+resource "aws_instance" "foo" {
+    foo = "foo"
+}
+
+resource "aws_instance" "bar" {
+    foo = "bar"
+}

terraform/test-fixtures/apply-count-dec/main.tf

@@ -0,0 +1,8 @@
+resource "aws_instance" "foo" {
+    foo = "foo"
+    count = 2
+}
+
+resource "aws_instance" "bar" {
+    foo = "bar"
+}