stride3d/stride · error · InvalidOperationException

[ . ] must be in

Error message

[{nameof(Description)}.{nameof(Description.Scope)}] must be {TemplateScope.Session} in {GetType().Name}

What it means

TemplateGeneratorParameters.ValidateParameters enforces that a generator's Description.Scope is TemplateScope.Session (and that Session is non-null). This InvalidOperationException is thrown when a generator whose type derives from this parameters class is invoked with a Description configured for a different scope.

Solutions

1. Set Description.Scope = TemplateScope.Session on the generator's parameters/template description
2. If a different scope is intended, derive from the appropriate parameters/generator base class instead of the Session-scoped one
3. Check the template's .tpl/YAML description for a mismatched Scope value and fix it
4. Also ensure Session is assigned, since the same ValidateParameters checks it next

Example fix

// before
Description = new TemplateDescription { Name = "MySessionTpl", Scope = TemplateScope.Package }
// after
Description = new TemplateDescription { Name = "MySessionTpl", Scope = TemplateScope.Session }

if (parameters.Description.Scope != TemplateScope.Session) throw new InvalidOperationException("Session-scoped generator requires TemplateScope.Session");
if (parameters.Session == null) throw new InvalidOperationException("Session must be set");

bool IsValidSessionTemplateParams(TemplateGeneratorParameters p) => p.Description?.Scope == TemplateScope.Session && p.Session != null;

try { generator.Run(parameters); } catch (InvalidOperationException ex) when (ex.Message.Contains("Scope")) { log.Error($"Template scope misconfigured: {ex.Message}"); throw; }

When it happens

Trigger: Invoking a template generator whose TemplateGeneratorParameters.Description.Scope was set to something other than TemplateScope.Session (e.g. Package scope) — typically from a custom template definition or a copy of an existing template whose scope was not updated.

Common situations: Writing a custom session-level template by copying a package-level template's Description without changing Scope; editing .tpl template descriptions by hand; upgrading Stride and introducing new scopes that conflict with old descriptions.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• [ ] cannot be null in
• [ . ] must be in
• [ ] cannot be null in
• [ . ] must be in
• [ ] cannot be null in

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/c916ab315192d1a7. Report an issue: GitHub.

Appendix: source

Thrown at sources/assets/Stride.Core.Assets/Templates/TemplateGeneratorParameters.cs:23

using Stride.Core.IO;

namespace Stride.Core.Assets.Templates;

public sealed class SessionTemplateGeneratorParameters : TemplateGeneratorParameters
{
    /// <summary>
    /// Gets or sets the current session.
    /// </summary>
    /// <value>The session.</value>
    public PackageSession Session { get; set; }

    protected override void ValidateParameters()
    {
        base.ValidateParameters();

        if (Description.Scope != TemplateScope.Session)
        {
            throw new InvalidOperationException($"[{nameof(Description)}.{nameof(Description.Scope)}] must be {TemplateScope.Session} in {GetType().Name}");
        }
        if (Session == null)
        {
            throw new InvalidOperationException($"[{nameof(Session)}] cannot be null in {GetType().Name}");
        }
    }
}

public class PackageTemplateGeneratorParameters : TemplateGeneratorParameters
{
    public PackageTemplateGeneratorParameters()
    {
    }

    public PackageTemplateGeneratorParameters(TemplateGeneratorParameters parameters, Package package)
        : base(parameters)
    {
        Package = package;

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