Diagnostics

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The source generator enforces correct usage at compile time via four diagnostic codes.

Diagnostic Table

Code	Severity	Condition	Remediation
ZA001	Error	[Specification] applied to a class	Change class to struct
ZA002	Error	Struct does not implement ISpecification<T>	Add : ISpecification<YourType>
ZA003	Error	Struct is not declared partial	Add partial modifier
ZA004	Warning	Struct is not declared readonly	Add readonly modifier

ZA001 — Not a struct

// ❌ Error ZA001
[Specification]
public class ActiveUserSpec : ISpecification<User> { ... }

// ✅ Fix
[Specification]
public readonly partial struct ActiveUserSpec : ISpecification<User> { ... }

ZA002 — Missing ISpecification<T>

// ❌ Error ZA002
[Specification]
public readonly partial struct ActiveUserSpec { ... }

// ✅ Fix
[Specification]
public readonly partial struct ActiveUserSpec : ISpecification<User> { ... }

ZA003 — Not partial

// ❌ Error ZA003
[Specification]
public readonly struct ActiveUserSpec : ISpecification<User> { ... }

// ✅ Fix
[Specification]
public readonly partial struct ActiveUserSpec : ISpecification<User> { ... }

ZA004 — Not readonly (Warning)

// ⚠️ Warning ZA004
[Specification]
public partial struct ActiveUserSpec : ISpecification<User> { ... }

// ✅ Fix
[Specification]
public readonly partial struct ActiveUserSpec : ISpecification<User> { ... }

readonly prevents the compiler from emitting defensive copies when passing the struct by value, which is important for performance.