command/meta: always ask for unset variable input

command/apply_test.go

@@ -407,6 +407,47 @@ func TestApply_input(t *testing.T) {
 	}
 }
 
+// When only a partial set of the variables are set, Terraform
+// should still ask for the unset ones by default (with -input=true)
+func TestApply_inputPartial(t *testing.T) {
+	// Disable test mode so input would be asked
+	test = false
+	defer func() { test = true }()
+
+	// Set some default reader/writers for the inputs
+	defaultInputReader = bytes.NewBufferString("one\ntwo\n")
+	defaultInputWriter = new(bytes.Buffer)
+
+	statePath := testTempFile(t)
+
+	p := testProvider()
+	ui := new(cli.MockUi)
+	c := &ApplyCommand{
+		Meta: Meta{
+			ContextOpts: testCtxConfig(p),
+			Ui:          ui,
+		},
+	}
+
+	args := []string{
+		"-state", statePath,
+		"-var", "foo=foovalue",
+		testFixturePath("apply-input-partial"),
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	expected := strings.TrimSpace(`
+<no state>
+Outputs:
+
+bar = one
+foo = foovalue
+	`)
+	testStateOutput(t, statePath, expected)
+}
+
 func TestApply_noArgs(t *testing.T) {
 	cwd, err := os.Getwd()
 	if err != nil {

command/meta.go

@@ -221,10 +221,8 @@ func (m *Meta) InputMode() terraform.InputMode {
 
 	var mode terraform.InputMode
 	mode |= terraform.InputModeProvider
-	if len(m.variables) == 0 {
-		mode |= terraform.InputModeVar
-		mode |= terraform.InputModeVarUnset
-	}
+	mode |= terraform.InputModeVar
+	mode |= terraform.InputModeVarUnset
 
 	return mode
 }

command/meta_test.go

@@ -175,7 +175,11 @@ func TestMetaInputMode_vars(t *testing.T) {
 		t.Fatalf("err: %s", err)
 	}
 
-	if m.InputMode()&terraform.InputModeVar != 0 {
+	if m.InputMode()&terraform.InputModeVar == 0 {
+		t.Fatalf("bad: %#v", m.InputMode())
+	}
+
+	if m.InputMode()&terraform.InputModeVarUnset == 0 {
 		t.Fatalf("bad: %#v", m.InputMode())
 	}
 }

command/test-fixtures/apply-input-partial/main.tf

@@ -0,0 +1,5 @@
+variable "foo" {}
+variable "bar" {}
+
+output "foo" { value = "${var.foo}" }
+output "bar" { value = "${var.bar}" }

terraform/context.go

@@ -22,7 +22,8 @@ const (
 	// InputModeVar asks for all variables
 	InputModeVar InputMode = 1 << iota
 
-	// InputModeVarUnset asks for variables which are not set yet
+	// InputModeVarUnset asks for variables which are not set yet.
+	// InputModeVar must be set for this to have an effect.
 	InputModeVarUnset
 
 	// InputModeProvider asks for provider variables