Spec: LC013 - Disposed Context Query Leak

Goal

Detect when an IQueryable or IAsyncEnumerable is returned from a method while the DbContext that created it is disposed.

The Problem

IQueryable and IAsyncEnumerable use deferred execution. If the DbContext is disposed (e.g., at the end of a using block), any attempt to run the query later will result in an ObjectDisposedException.

Example Violation

public IQueryable<User> GetUsers()
{
    using var db = new AppDbContext();
    var query = db.Users.Where(u => u.Active);

    // Violation: Caller cannot use this query because db is about to be disposed
    return query;
}

The Fix

Materialize the query before returning, or ensure the context lifetime is managed correctly (e.g., by the DI container).

public List<User> GetUsers()
{
    using var db = new AppDbContext();
    // Correct: Data is fetched before context is disposed
    return db.Users.Where(u => u.Active).ToList();
}

Analyzer Logic

• Tracks the returned query back through single-assignment local aliases in the same executable root.
• Handles conditional, coalesce, and switch-expression returns branch by branch.
• Only reports when the origin is a disposed local DbContext.
• Continues through known LINQ/EF query-chain operators, but treats arbitrary project extension methods as boundaries because they may materialize before returning IQueryable.
• Ignores nested local-function and lambda returns to avoid false positives when the outer method materializes the query before exiting.
• No automatic code fix is offered for LC013 in this pass.

ID: LC013

Category: Reliability

Severity: Warning