test non-string env var input variables

Non-string input variables taken from the environment initially need to
be parsed and stored as string, since there is no type associated type
information. Make sure these are correctly handled when validated during
apply.

internal/command/apply_test.go

@@ -964,16 +964,10 @@ func TestApply_planWithVarFileChangingVariableValue(t *testing.T) {
 	}
 }
 
-func TestApply_planVars(t *testing.T) {
-	// This test ensures that it isn't allowed to set non-ephemeral input
-	// variables when applying from a saved plan file, since in that case the
-	// variable values come from the saved plan file.
-	//
-	// This situation was originally checked by the apply command itself,
-	// and that's what this test was originally exercising. This rule
-	// is now enforced by the "local" backend instead, but this test
-	// is still valid since the command instance delegates to the
-	// local backend.
+func TestApply_planUndeclaredVars(t *testing.T) {
+	// This test ensures that it isn't allowed to set undeclared input variables
+	// when applying from a saved plan file, since in that case the variable
+	// values come from the saved plan file.
 
 	planPath := applyFixturePlanFile(t)
 	statePath := testTempFile(t)
@@ -1076,7 +1070,6 @@ foo = "bar"
 
 		"with planfile passing ephemeral variable through environment variable": func(t *testing.T, c *ApplyCommand, statePath, planPath string, done func(*testing.T) *terminal.TestOutput) {
 			t.Setenv("TF_VAR_foo", "bar")
-			defer t.Setenv("TF_VAR_foo", "")
 
 			args := []string{
 				"-state", statePath,
@@ -1168,7 +1161,7 @@ foo = "bar"
 
 		"without planfile passing ephemeral variable through environment variable": func(t *testing.T, c *ApplyCommand, statePath, planPath string, done func(*testing.T) *terminal.TestOutput) {
 			t.Setenv("TF_VAR_foo", "bar")
-			defer t.Setenv("TF_VAR_foo", "")
+			t.Setenv("TF_VAR_unused", `{key:"val"}`)
 
 			args := []string{
 				"-state", statePath,

internal/command/testdata/apply-ephemeral-variable/main.tf

@@ -9,6 +9,11 @@ variable "bar" {
   ephemeral = true
 }
 
+variable "unused" {
+  type = map(string)
+  default = null
+}
+
 resource "test_instance" "foo" {
   ami = "bar"
 }