Allow map variables from json

A JSON object will be decoded as a list with a single map value. This
will be properly coerced later, so let it through the initial config
semantic checks.

terraform/semantics.go

@@ -108,30 +108,25 @@ func smcUserVariables(c *config.Config, vs map[string]interface{}) []error {
 			switch proposedValue.(type) {
 			case string:
 				continue
-			default:
-				errs = append(errs, fmt.Errorf("variable %s should be type %s, got %s",
-					name, declaredType.Printable(), hclTypeName(proposedValue)))
 			}
 		case config.VariableTypeMap:
-			switch proposedValue.(type) {
+			switch v := proposedValue.(type) {
 			case map[string]interface{}:
 				continue
-			default:
-				errs = append(errs, fmt.Errorf("variable %s should be type %s, got %s",
-					name, declaredType.Printable(), hclTypeName(proposedValue)))
+			case []map[string]interface{}:
+				// if we have a list of 1 map, it will get coerced later as needed
+				if len(v) == 1 {
+					continue
+				}
 			}
 		case config.VariableTypeList:
 			switch proposedValue.(type) {
 			case []interface{}:
 				continue
-			default:
-				errs = append(errs, fmt.Errorf("variable %s should be type %s, got %s",
-					name, declaredType.Printable(), hclTypeName(proposedValue)))
 			}
-		default:
-			errs = append(errs, fmt.Errorf("variable %s should be type %s, got %s",
-				name, declaredType.Printable(), hclTypeName(proposedValue)))
 		}
+		errs = append(errs, fmt.Errorf("variable %s should be type %s, got %s",
+			name, declaredType.Printable(), hclTypeName(proposedValue)))
 	}
 
 	// TODO(mitchellh): variables that are unknown

terraform/semantics_test.go

@@ -38,3 +38,20 @@ func TestSMCUserVariables(t *testing.T) {
 	}
 
 }
+
+func TestSMCUserVariables_mapFromJSON(t *testing.T) {
+	c := testConfig(t, "uservars-map")
+
+	// ensure that a single map in a list can satisfy a map variable, since it
+	// will be coerced later to a map
+	err := smcUserVariables(c, map[string]interface{}{
+		"test_map": []map[string]interface{}{
+			map[string]interface{}{
+				"foo": "bar",
+			},
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+}

terraform/test-fixtures/uservars-map/main.tf

@@ -0,0 +1,3 @@
+variable "test_map" {
+  type = "map"
+}