Merge pull request #20546 from hashicorp/jbardin/backend-init-panic

don't panic of the users aborts backend input

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)

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,

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())