Merge pull request #2386 from hashicorp/b-template-variable-change-failure

provider/template: don't error when rendering fails in Exists

builtin/providers/template/resource.go

@@ -5,6 +5,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"path/filepath"
 
@@ -75,7 +76,13 @@ func Delete(d *schema.ResourceData, meta interface{}) error {
 func Exists(d *schema.ResourceData, meta interface{}) (bool, error) {
 	rendered, err := render(d)
 	if err != nil {
-		return false, err
+		if _, ok := err.(templateRenderError); ok {
+			log.Printf("[DEBUG] Got error while rendering in Exists: %s", err)
+			log.Printf("[DEBUG] Returning false so the template re-renders using latest variables from config.")
+			return false, nil
+		} else {
+			return false, err
+		}
 	}
 	return hash(rendered) == d.Id(), nil
 }
@@ -87,6 +94,8 @@ func Read(d *schema.ResourceData, meta interface{}) error {
 	return nil
 }
 
+type templateRenderError error
+
 var readfile func(string) ([]byte, error) = ioutil.ReadFile // testing hook
 
 func render(d *schema.ResourceData) (string, error) {
@@ -105,7 +114,9 @@ func render(d *schema.ResourceData) (string, error) {
 
 	rendered, err := execute(string(buf), vars)
 	if err != nil {
-		return "", fmt.Errorf("failed to render %v: %v", filename, err)
+		return "", templateRenderError(
+			fmt.Errorf("failed to render %v: %v", filename, err),
+		)
 	}
 
 	return rendered, nil

builtin/providers/template/resource_test.go

@@ -34,15 +34,7 @@ func TestTemplateRendering(t *testing.T) {
 			Providers: testProviders,
 			Steps: []r.TestStep{
 				r.TestStep{
-					Config: `
-resource "template_file" "t0" {
-	filename = "mock"
-	vars = ` + tt.vars + `
-}
-output "rendered" {
-    value = "${template_file.t0.rendered}"
-}
-`,
+					Config: testTemplateConfig(tt.vars),
 					Check: func(s *terraform.State) error {
 						got := s.RootModule().Outputs["rendered"]
 						if tt.want != got {
@@ -55,3 +47,55 @@ output "rendered" {
 		})
 	}
 }
+
+// https://github.com/hashicorp/terraform/issues/2344
+func TestTemplateVariableChange(t *testing.T) {
+	steps := []struct {
+		vars     string
+		template string
+		want     string
+	}{
+		{`{a="foo"}`, `${a}`, `foo`},
+		{`{b="bar"}`, `${b}`, `bar`},
+	}
+
+	var testSteps []r.TestStep
+	for i, step := range steps {
+		testSteps = append(testSteps, r.TestStep{
+			PreConfig: func(template string) func() {
+				return func() {
+					readfile = func(string) ([]byte, error) {
+						return []byte(template), nil
+					}
+				}
+			}(step.template),
+			Config: testTemplateConfig(step.vars),
+			Check: func(i int, want string) r.TestCheckFunc {
+				return func(s *terraform.State) error {
+					got := s.RootModule().Outputs["rendered"]
+					if want != got {
+						return fmt.Errorf("[%d] got:\n%q\nwant:\n%q\n", i, got, want)
+					}
+					return nil
+				}
+			}(i, step.want),
+		})
+	}
+
+	r.Test(t, r.TestCase{
+		Providers: testProviders,
+		Steps:     testSteps,
+	})
+}
+
+func testTemplateConfig(vars string) string {
+	return `
+resource "template_file" "t0" {
+	filename = "mock"
+	vars = ` + vars + `
+}
+output "rendered" {
+    value = "${template_file.t0.rendered}"
+}
+	`
+}

helper/resource/testing.go

@@ -60,6 +60,10 @@ type TestCase struct {
 // potentially complex update logic. In general, simply create/destroy
 // tests will only need one step.
 type TestStep struct {
+	// PreConfig is called before the Config is applied to perform any per-step
+	// setup that needs to happen
+	PreConfig func()
+
 	// Config a string of the configuration to give to Terraform.
 	Config string
 
@@ -160,6 +164,10 @@ func testStep(
 	opts terraform.ContextOpts,
 	state *terraform.State,
 	step TestStep) (*terraform.State, error) {
+	if step.PreConfig != nil {
+		step.PreConfig()
+	}
+
 	cfgPath, err := ioutil.TempDir("", "tf-test")
 	if err != nil {
 		return state, fmt.Errorf(