From 052345abfe2f59b7ce724818cd205e56fd009ea7 Mon Sep 17 00:00:00 2001
From: James Nugent <james@jen20.com>
Date: Sun, 12 Jun 2016 12:33:05 +0200
Subject: [PATCH] core: Fix empty multi-variable type

Previously, interpolation of multi-variables was returning an empty
variable if the resource count was 0. The empty variable was defined as
TypeString, Value "". This means that empty resource counts fail type
checking for interpolation functions which operate on lists.

Instead, return an empty list if the count is 0. A context test tests
this against further regression. Also add a regression test covering the
case of a single count multi-variable.

In order to make the context testing framework deal with this change it
was necessary to special case empty lists in the test diff function.

Fixes #7002
---
 terraform/context_apply_test.go               | 63 +++++++++++++++++++
 terraform/context_test.go                     |  8 ++-
 terraform/interpolate.go                      |  2 +-
 .../apply-resource-count-one-list/main.tf     |  7 +++
 .../apply-resource-count-zero-list/main.tf    |  7 +++
 5 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 terraform/test-fixtures/apply-resource-count-one-list/main.tf
 create mode 100644 terraform/test-fixtures/apply-resource-count-zero-list/main.tf

diff --git a/terraform/context_apply_test.go b/terraform/context_apply_test.go
index d643991590..a287abdd80 100644
--- a/terraform/context_apply_test.go
+++ b/terraform/context_apply_test.go
@@ -48,6 +48,69 @@ func TestContext2Apply(t *testing.T) {
 	}
 }
 
+func TestContext2Apply_resourceCountOneList(t *testing.T) {
+	m := testModule(t, "apply-resource-count-one-list")
+	p := testProvider("null")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"null": testProviderFuncFixed(p),
+		},
+	})
+
+	if _, err := ctx.Plan(); 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(`null_resource.foo:
+  ID = foo
+
+Outputs:
+
+test = [foo]`)
+	if actual != expected {
+		t.Fatalf("expected: \n%s\n\ngot: \n%s\n", expected, actual)
+	}
+}
+func TestContext2Apply_resourceCountZeroList(t *testing.T) {
+	m := testModule(t, "apply-resource-count-zero-list")
+	p := testProvider("null")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"null": testProviderFuncFixed(p),
+		},
+	})
+
+	if _, err := ctx.Plan(); 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(`<no state>
+Outputs:
+
+test = []`)
+	if actual != expected {
+		t.Fatalf("expected: \n%s\n\ngot: \n%s\n", expected, actual)
+	}
+}
+
 func TestContext2Apply_mapVarBetweenModules(t *testing.T) {
 	m := testModule(t, "apply-map-var-through-module")
 	p := testProvider("null")
diff --git a/terraform/context_test.go b/terraform/context_test.go
index 897539f6dc..6d3f1e57f8 100644
--- a/terraform/context_test.go
+++ b/terraform/context_test.go
@@ -2,6 +2,7 @@ package terraform
 
 import (
 	"fmt"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
@@ -166,7 +167,12 @@ func testDiffFn(
 
 		attrDiff := &ResourceAttrDiff{
 			Old: "",
-			New: v.(string),
+		}
+
+		if reflect.DeepEqual(v, []interface{}{}) {
+			attrDiff.New = ""
+		} else {
+			attrDiff.New = v.(string)
 		}
 
 		if k == "require_new" {
diff --git a/terraform/interpolate.go b/terraform/interpolate.go
index bb0d22144d..f03154141c 100644
--- a/terraform/interpolate.go
+++ b/terraform/interpolate.go
@@ -487,7 +487,7 @@ func (i *Interpolater) computeResourceMultiVariable(
 
 	// If we have no module in the state yet or count, return empty
 	if module == nil || len(module.Resources) == 0 || count == 0 {
-		return &ast.Variable{Type: ast.TypeString, Value: ""}, nil
+		return &ast.Variable{Type: ast.TypeList, Value: []ast.Variable{}}, nil
 	}
 
 	var values []string
diff --git a/terraform/test-fixtures/apply-resource-count-one-list/main.tf b/terraform/test-fixtures/apply-resource-count-one-list/main.tf
new file mode 100644
index 0000000000..0aeb75b1af
--- /dev/null
+++ b/terraform/test-fixtures/apply-resource-count-one-list/main.tf
@@ -0,0 +1,7 @@
+resource "null_resource" "foo" {
+  count = 1
+}
+
+output "test" {
+  value = "${sort(null_resource.foo.*.id)}"
+}
diff --git a/terraform/test-fixtures/apply-resource-count-zero-list/main.tf b/terraform/test-fixtures/apply-resource-count-zero-list/main.tf
new file mode 100644
index 0000000000..6d9b4d55d2
--- /dev/null
+++ b/terraform/test-fixtures/apply-resource-count-zero-list/main.tf
@@ -0,0 +1,7 @@
+resource "null_resource" "foo" {
+  count = 0
+}
+
+output "test" {
+  value = "${sort(null_resource.foo.*.id)}"
+}