config: Resource.Count should type check

Fixes #11800

Type check the value of count so we don't panic on the conversion.

I wondered "why didn't we do this before?" There is no excuse for NOT
doing it at all but the reasoning was beacuse prior to the list/map work
in 0.7, the value couldn't be anything other than a string since any
primitive can turn into a string.

Regardless, we should've always done this.

config/config.go

@@ -212,7 +212,14 @@ func (r *Module) Id() string {
 
 // Count returns the count of this resource.
 func (r *Resource) Count() (int, error) {
-	v, err := strconv.ParseInt(r.RawCount.Value().(string), 0, 0)
+	raw := r.RawCount.Value()
+	count, ok := r.RawCount.Value().(string)
+	if !ok {
+		return 0, fmt.Errorf(
+			"expected count to be a string or int, got %T", raw)
+	}
+
+	v, err := strconv.ParseInt(count, 0, 0)
 	if err != nil {
 		return 0, err
 	}

config/config_test.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/hashicorp/hil/ast"
 	"github.com/hashicorp/terraform/helper/logging"
 )
 
@@ -98,6 +99,24 @@ func TestConfigCount_string(t *testing.T) {
 	}
 }
 
+// Terraform GH-11800
+func TestConfigCount_list(t *testing.T) {
+	c := testConfig(t, "count-list")
+
+	// The key is to interpolate so it doesn't fail parsing
+	c.Resources[0].RawCount.Interpolate(map[string]ast.Variable{
+		"var.list": ast.Variable{
+			Value: []ast.Variable{},
+			Type:  ast.TypeList,
+		},
+	})
+
+	_, err := c.Resources[0].Count()
+	if err == nil {
+		t.Fatal("should error")
+	}
+}
+
 func TestConfigCount_var(t *testing.T) {
 	c := testConfig(t, "count-var")
 	_, err := c.Resources[0].Count()

config/test-fixtures/count-list/main.tf

@@ -0,0 +1,3 @@
+resource "foo" "bar" {
+    count = "${var.list}"
+}