BRO1125: Use lambda syntax

(s, e) => { } instead of delegate (object s, EventArgs e) { }. Replaces StyleCop SA1130.

Example

Before

using System;
using System.Collections.Generic;

public class Button
{
    public event EventHandler? Clicked;

    public void Wire(List<string> log)
    {
        Clicked += delegate { log.Add("clicked"); };
        log.RemoveAll(delegate (string entry) { return entry.Length == 0; });
    }
}

After

using System;
using System.Collections.Generic;

public class Button
{
    public event EventHandler? Clicked;

    public void Wire(List<string> log)
    {
        Clicked += (sender, e) => { log.Add("clicked"); };
        log.RemoveAll(entry => { return entry.Length == 0; });
    }
}

Why

Lambdas are the modern form of anonymous methods; mixing both makes code look older than it is.

How the fix works

Like StyleCop's fix: the parameter types are dropped, async stays, and a cast's operand gets parentheses ((Action)(() => { })). A delegate { } without a parameter list gets the delegate's parameter names, made unique against names in scope and in the body (sender1). The body isn't touched. The lambda is bound in place first: it must convert to the same delegate type and, as an argument, call the same overload.

Not reported

• Calls where the lambda would pick another overload or be ambiguous: Run(delegate { return 1; }) with Run(Func<int>) and Run(Expression<Func<int>>) would call the expression overload.
• Anonymous methods without a target type (var f = delegate (int x) { ... }: a lambda without parameter types has none), parameters with ref/out/params, attributes or defaults, a missing parameter list for a delegate with ref/out parameters, and comments between delegate and the body.

Compared with StyleCop

Same positions, except the cases above (StyleCop checks overloads only for arguments, so its fix for a var breaks the build) and calls like list.ForEach(delegate (int item) { ... }), which StyleCop misses and StyleBro converts. StyleCop's fix also leaves two spaces after = and pulls a body on its own line up behind =>.