MM-9977: test config.SetDefaults leaves nothing nil (#8610)

* MM-9977: test config.SetDefaults leaves nothing nil

* clarify test default config test cases

* comment re: allowing nil slice

* extend config SetDefaults to handle partially initialized configs

model/utils.go

@@ -15,9 +15,11 @@ import (
 	"net/http"
 	"net/mail"
 	"net/url"
+	"reflect"
 	"regexp"
 	"strconv"
 	"strings"
+	"testing"
 	"time"
 	"unicode"
 
@@ -469,3 +471,60 @@ func IsValidId(value string) bool {
 
 	return true
 }
+
+// checkNowhereNil checks that the given interface value is not nil, and if a struct, that all of
+// its public fields are also nowhere nil
+func checkNowhereNil(t *testing.T, name string, value interface{}) bool {
+	if value == nil {
+		return false
+	}
+
+	v := reflect.ValueOf(value)
+	switch v.Type().Kind() {
+	case reflect.Ptr:
+		if v.IsNil() {
+			t.Logf("%s was nil", name)
+			return false
+		}
+
+		return checkNowhereNil(t, fmt.Sprintf("(*%s)", name), v.Elem().Interface())
+
+	case reflect.Map:
+		if v.IsNil() {
+			t.Logf("%s was nil", name)
+			return false
+		}
+
+		// Don't check map values
+		return true
+
+	case reflect.Struct:
+		nowhereNil := true
+		for i := 0; i < v.NumField(); i++ {
+			f := v.Field(i)
+			// Ignore unexported fields
+			if v.Type().Field(i).PkgPath != "" {
+				continue
+			}
+
+			nowhereNil = nowhereNil && checkNowhereNil(t, fmt.Sprintf("%s.%s", name, v.Type().Field(i).Name), f.Interface())
+		}
+
+		return nowhereNil
+
+	case reflect.Array:
+		fallthrough
+	case reflect.Chan:
+		fallthrough
+	case reflect.Func:
+		fallthrough
+	case reflect.Interface:
+		fallthrough
+	case reflect.UnsafePointer:
+		t.Logf("unhandled field %s, type: %s", name, v.Type().Kind())
+		return false
+
+	default:
+		return true
+	}
+}