TRLS018 — Unsafe access to Value in LINQ expression

• Severity: Warning
• Category: Trellis

What it detects

Flags .Value access on a LINQ lambda parameter inside projections, grouping, ordering, and dictionary-building operations unless an earlier Where(...) guard proves the value is safe.

Why it matters

Collection pipelines make it easy to forget that some items may be failures or empty values. One unsafe access can throw for the whole query.

Warning

The analyzer understands guard chains like .Where(x => x.IsSuccess) and .Where(x => x.HasValue). Without that filter, .Value is treated as unsafe.

Bad example

using System.Collections.Generic;
using System.Linq;
using Trellis;

static class Example
{
    public static List<int> Bad(IEnumerable<Result<int>> values) =>
        values.Select(result => result.Value).ToList();
}

Good example

using System.Collections.Generic;
using System.Linq;
using Trellis;

static class Example
{
    public static List<int> Good(IEnumerable<Result<int>> values) =>
        values
            .Where(result => result.IsSuccess)
            .Select(result => result.Value)
            .ToList();
}

Code fix available

No.

Configuration

Use standard Roslyn configuration if you need to suppress this rule in a specific scope.

dotnet_diagnostic.TRLS018.severity = none

#pragma warning disable TRLS018
// Intentional: documented exception or test-only pattern.
#pragma warning restore TRLS018

Tip

Filter first, then project. If you need both success and failure paths, use Match inside the projection instead of .Value.