Description

When binding to a type with a constructor that has a default string parameter, the generator emits code that doesn't compile.

C:\scratch\configStringCtorParam\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Config
uration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs(77,27): error CS0103: The name 's'
 does not exist in the current context [C:\scratch\configStringCtorParam\configStringCtorParam.csproj]

The code generated looks like this:

 public static SD InitializeSD(IConfiguration configuration, BinderOptions? binderOptions)
        {
            if (configuration["S"] is string value1)
            {
                string s = value1;
            }

            return new SD(s);
        }

Bug is likely in the EmitBindImplForMember method but I haven't tracked it down. I suspect there's a disagreement between the case where the member is string parseable but also has a default value. This same repro works when removing the default value.

Reproduction Steps

using Microsoft.Extensions.Configuration;
var c = new ConfigurationBuilder().Build();
var x = c.Get<SD>();
Console.WriteLine(x);

public class SD
{
    public SD(string s = "default value") { S = s; }
    public string S { get;}
    public override string ToString() => S;
}

Expected behavior

Compiles successfully.

Actual behavior

Compilation failure.

Regression?

No

Known Workarounds

Remove default value from ctor param.

Configuration

No response

Other information

No response