Analyzers

MCP form elicitation is easy to get slightly wrong: a nested object on From<T>(), two properties that camelCase to the same name, a lambda that isn’t x => x.Email. Runtime skips or throws. The analyzers in McpEssentials.Core turn those mistakes into IDE squiggles and dotnet build diagnostics. They fire on FormElicitation.From<T>() and on expression starters (Exclude, String, Email, …). String-named Create() fields are whatever you add, so they are not analyzed.

Ships in Core

dotnet add package McpEssentials.Core is enough. No extra package for everyday use.

Six IDs

MCPESS001–006. Warnings, errors, and one info. All in the Usage category.

Same chain

.Exclude(x => x.Home) on the From call that seeded Home suppresses MCPESS001 for that property.

Install

With Core
Analyzers only

Core already packs CloudNimble.McpEssentials.Analyzers.dll under analyzers/dotnet/cs. Adding Core to a project enables the diagnostics.

dotnet add package McpEssentials.Core

Use McpEssentials.Analyzers when you want the analyzer assembly without taking Core as a runtime dependency, or to pin analyzer versions separately.

dotnet add package McpEssentials.Analyzers

Rebuild after adding Core. Roslyn loads analyzers from the package; a running IDE may need a restart before squiggles appear.

What they watch

From a type

FormElicitation.From<T>("…") and new FormElicitationBuilder<T>("…"). Public instance properties are checked against the same mapping rules as runtime.

Expression starters

Exclude, String, Email, Uri, Date, DateTime, Integer, Number, Boolean, Choice, and MultiChoice when the first argument is a lambda.

The fluent chain

Exclude calls on the same expression as From are collected so skipped properties you already excluded do not warn.

FormElicitation.Create("…").String("filter") is metadata-driven. There is no CLR property to inspect, so the analyzers stay quiet. That is the path for OData $metadata and other runtime catalogs.

Diagnostics

MCPESS001 — unmappable property

Warning. From<T>() skips public properties the MCP form schema cannot represent: nested objects, dictionaries, TimeSpan, byte[], string[], indexers, write-only and static members.

public class SignupForm
{
    public string Name { get; set; }
    public Address Home { get; set; } // skipped at runtime
}

FormElicitation.From<SignupForm>("Sign up");
// MCPESS001: Property 'Home' on 'SignupForm' is skipped by FormElicitation.From.

FormElicitation.From<SignupForm>("Sign up")
    .Exclude(x => x.Home);

An empty type (no public properties) is a confirm dialog and does not warn.

MCPESS002 — colliding wire names

Error. Two properties camelCase to the same JSON name. Runtime throws InvalidOperationException at From. The analyzer fails the build instead.

public class CollisionForm
{
    public string EmailAddress { get; set; }
    public string emailAddress { get; set; } // both become emailAddress
}

FormElicitation.From<CollisionForm>("m");
// MCPESS002: Properties 'EmailAddress' and 'emailAddress' on 'CollisionForm'
// both map to form field 'emailAddress'.

FormElicitation.From<CollisionForm>("m")
    .Exclude(x => x.emailAddress);

MCPESS003 — nested or invalid lambda

Error. Expression starters and Exclude require a simple property access on the form type, the same rule as FormElicitationProperty.From. Nested members, method calls, and fields fail.

FormElicitation.From<Order>("m")
    .Exclude(x => x.Address.City);   // nested

FormElicitation.From<Order>("m")
    .String(x => x.Name.Trim());     // method

FormElicitation.From<Order>("m")
    .Exclude(x => x.Address)
    .String(x => x.Name);

MCPESS004 — Exclude of something that was never a field

Info. Exclude of an unmappable property is a successful no-op at runtime. The analyzer tells you so you do not think you removed a field that was never seeded.

public class Form
{
    public string Name { get; set; }
    public Address Home { get; set; }
}

FormElicitation.From<Form>("m").Exclude(x => x.Home);
// MCPESS004: Exclude of 'Home' does nothing because the property is not a supported form field
// MCPESS001 is suppressed for Home on this From call.

MCPESS005 — From on a built-in

Warning. From<T>() expects a class or struct of public properties. string, primitives, enums, and arrays are not form DTOs.

FormElicitation.From<string>("m");
FormElicitation.From<int>("m");
FormElicitation.From<ColorChoice>("m");

FormElicitation.From<SignupForm>("m");
FormElicitation.Create("m").String("notes");

MCPESS006 — field added after Build

Warning. Build, ToXml, ToJson, ToDefinition, and ToInputRequest seal the form. A later starter or Exclude on that local would throw at runtime.

var form = FormElicitation.Create("m").String("trackingNumber");
form.Build();
form.Integer("quantity"); // MCPESS006

var form = FormElicitation.Create("m")
    .String("trackingNumber")
    .Integer("quantity");
form.Build();

Severity at a glance

Id	Severity	Default	Typical fix
MCPESS001	Warning	On	`.Exclude(x => x.Prop)` or change the property type
MCPESS002	Error	On	Rename or Exclude one of the colliding properties
MCPESS003	Error	On	Use `x => x.Email`, not nested access
MCPESS004	Info	On	Drop the `Exclude`, or leave it as documentation
MCPESS005	Warning	On	Pass a form DTO, or use `Create()`
MCPESS006	Warning	On	Add every field before `Build` / `ToXml` / `ToJson`

Suppress a diagnostic

Use this when the skip is deliberate and you do not want .Exclude on the chain.

Inline
EditorConfig
Project

#pragma warning disable MCPESS001
var form = FormElicitation.From<LegacyDto>("Continue");
#pragma warning restore MCPESS001

[*.cs]
dotnet_diagnostic.MCPESS001.severity = suggestion
dotnet_diagnostic.MCPESS004.severity = none

<PropertyGroup>
  <NoWarn>$(NoWarn);MCPESS004</NoWarn>
</PropertyGroup>

Do not suppress MCPESS002 or MCPESS003. Those match runtime exceptions. A warning you understand (MCPESS001 on a DTO you do not own) is the usual candidate.

What maps

The analyzer uses the same rules as FormElicitation.From<T>(). If Core would seed a field, MCPESS001 stays quiet.

Seeded

string, Guid, char, Uri, DateOnly, DateTime, DateTimeOffset, bool, integer types, float / double / decimal, enums, [Flags] enums, and sequences of enums (TEnum[], List<TEnum>, IEnumerable<TEnum>).

Skipped

Nested objects, Dictionary<,>, object, TimeSpan, byte[], string[], int[], indexers, write-only properties, static properties.

Form elicitation

Fluent schemas, ElicitAsync, and parking a form on a task.

FormElicitation API

Create, From<T>, and Bind<T>.

Authenticated tasks

Isolation, identity factory, and the samples.

Stores

Durable providers that persist the parked form.

Getting Started

API Reference

Ships in Core

Six IDs

Same chain

Install

What they watch

Diagnostics

Severity at a glance

Suppress a diagnostic

What maps

Form elicitation

FormElicitation API

Authenticated tasks

Stores

Ships in Core

Six IDs

Same chain

​Install

​What they watch

​Diagnostics

​Severity at a glance

​Suppress a diagnostic

​What maps

​Related

Form elicitation

FormElicitation API

Authenticated tasks

Stores

Install

What they watch

Diagnostics

Severity at a glance

Suppress a diagnostic

What maps

Related