Get rid of the list when parsing HCL maps for vars

When we parse a map from HCL, it's decoded into a list of maps because
HCL allows declaring a key multiple times to implicitly add it to a
list.  Since there's no terraform variable configuration that supports
this structure, we can always flatten a []map[string]interface{} value
to a map[string]interface{} and remove any type rrors trying to apply
that value.

command/flag_kv.go

@@ -111,6 +111,10 @@ func loadKVFile(rawPath string) (map[string]interface{}, error) {
 				"Decoding errors are usually caused by an invalid format.",
 			err)
 	}
+	err = flattenMultiMaps(result)
+	if err != nil {
+		return nil, err
+	}
 
 	return result, nil
 }
@@ -185,10 +189,34 @@ func parseVarFlagAsHCL(input string) (string, interface{}, error) {
 		return "", nil, fmt.Errorf("Cannot parse value for variable %s (%q) as valid HCL. Only one value may be specified.", probablyName, input)
 	}
 
-	for k, v := range decoded {
-		return k, v, nil
+	err = flattenMultiMaps(decoded)
+	if err != nil {
+		return probablyName, "", err
 	}
 
-	// Should be unreachable
-	return "", nil, fmt.Errorf("No value for variable: %s", input)
+	var k string
+	var v interface{}
+	for k, v = range decoded {
+		break
+	}
+	return k, v, nil
+}
+
+// Variables don't support any type that can be configured via multiple
+// declarations of the same HCL map, so any instances of
+// []map[string]interface{} are either a single map that can be flattened, or
+// are invalid config.
+func flattenMultiMaps(m map[string]interface{}) error {
+	for k, v := range m {
+		switch v := v.(type) {
+		case []map[string]interface{}:
+			switch {
+			case len(v) > 1:
+				return fmt.Errorf("multiple map declarations not supported for variables")
+			case len(v) == 1:
+				m[k] = v[0]
+			}
+		}
+	}
+	return nil
 }

command/flag_kv_test.go

@@ -2,10 +2,11 @@ package command
 
 import (
 	"flag"
-	"github.com/davecgh/go-spew/spew"
 	"io/ioutil"
 	"reflect"
 	"testing"
+
+	"github.com/davecgh/go-spew/spew"
 )
 
 func TestFlagStringKV_impl(t *testing.T) {
@@ -118,11 +119,9 @@ func TestFlagTypedKV(t *testing.T) {
 		{
 			`key={"hello" = "world", "foo" = "bar"}`,
 			map[string]interface{}{
-				"key": []map[string]interface{}{
-					map[string]interface{}{
-						"hello": "world",
-						"foo":   "bar",
-					},
+				"key": map[string]interface{}{
+					"hello": "world",
+					"foo":   "bar",
 				},
 			},
 			false,
@@ -169,6 +168,10 @@ func TestFlagKVFile(t *testing.T) {
 	inputLibucl := `
 foo = "bar"
 `
+	inputMap := `
+foo = {
+	k = "v"
+}`
 
 	inputJson := `{
 		"foo": "bar"}`
@@ -195,6 +198,16 @@ foo = "bar"
 			map[string]interface{}{"map.key": "foo"},
 			false,
 		},
+
+		{
+			inputMap,
+			map[string]interface{}{
+				"foo": map[string]interface{}{
+					"k": "v",
+				},
+			},
+			false,
+		},
 	}
 
 	path := testTempFile(t)