From 2adf5801d9582d607c6ed3742fd48a650e31df57 Mon Sep 17 00:00:00 2001
From: James Bardin <j.bardin@gmail.com>
Date: Fri, 1 Mar 2019 18:45:06 -0500
Subject: [PATCH] don't panic of the users aborts backend input

When the user aborts input, it may end up as an unknown value, which
needs to be converted to null for PrepareConfig.

Allow PrepareConfig to accept null config values in order to fill in
missing defaults.
---
 command/meta_backend.go       |  7 +++++++
 helper/schema/backend.go      |  6 +++++-
 helper/schema/backend_test.go | 21 ++++++++++++++++++++-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/command/meta_backend.go b/command/meta_backend.go
index 47ea97a76..de242932d 100644
--- a/command/meta_backend.go
+++ b/command/meta_backend.go
@@ -1038,6 +1038,13 @@ func (m *Meta) backendInitFromConfig(c *configs.Backend) (backend.Backend, cty.V
 		if err != nil {
 			diags = diags.Append(fmt.Errorf("Error asking for input to configure backend %q: %s", c.Type, err))
 		}
+
+		// We get an unknown here if the if the user aborted input, but we can't
+		// turn that into a config value, so set it to null and let the provider
+		// handle it in PrepareConfig.
+		if !configVal.IsKnown() {
+			configVal = cty.NullVal(configVal.Type())
+		}
 	}
 
 	newVal, validateDiags := b.PrepareConfig(configVal)
diff --git a/helper/schema/backend.go b/helper/schema/backend.go
index 64c3b9f69..c8d8ae28c 100644
--- a/helper/schema/backend.go
+++ b/helper/schema/backend.go
@@ -182,7 +182,11 @@ func (b *Backend) Configure(obj cty.Value) tfdiags.Diagnostics {
 // that should be populated enough to appease the not-yet-updated functionality
 // in this package. This should be removed once everything is updated.
 func (b *Backend) shimConfig(obj cty.Value) *terraform.ResourceConfig {
-	shimMap := hcl2shim.ConfigValueFromHCL2(obj).(map[string]interface{})
+	shimMap, ok := hcl2shim.ConfigValueFromHCL2(obj).(map[string]interface{})
+	if !ok {
+		// If the configVal was nil, we still want a non-nil map here.
+		shimMap = map[string]interface{}{}
+	}
 	return &terraform.ResourceConfig{
 		Config: shimMap,
 		Raw:    shimMap,
diff --git a/helper/schema/backend_test.go b/helper/schema/backend_test.go
index 609ce5967..8b0336fe0 100644
--- a/helper/schema/backend_test.go
+++ b/helper/schema/backend_test.go
@@ -31,6 +31,21 @@ func TestBackendPrepare(t *testing.T) {
 			true,
 		},
 
+		{
+			"Null config",
+			&Backend{
+				Schema: map[string]*Schema{
+					"foo": &Schema{
+						Required: true,
+						Type:     TypeString,
+					},
+				},
+			},
+			nil,
+			map[string]cty.Value{},
+			true,
+		},
+
 		{
 			"Basic required field set",
 			&Backend{
@@ -111,7 +126,11 @@ func TestBackendPrepare(t *testing.T) {
 
 	for i, tc := range cases {
 		t.Run(fmt.Sprintf("%d-%s", i, tc.Name), func(t *testing.T) {
-			configVal, diags := tc.B.PrepareConfig(cty.ObjectVal(tc.Config))
+			cfgVal := cty.NullVal(cty.Object(map[string]cty.Type{}))
+			if tc.Config != nil {
+				cfgVal = cty.ObjectVal(tc.Config)
+			}
+			configVal, diags := tc.B.PrepareConfig(cfgVal)
 			if diags.HasErrors() != tc.Err {
 				for _, d := range diags {
 					t.Error(d.Description())