Configuration Manager takes providers priority differently

[DeagleGross]

Description

ASP.NET configuration started to behave differently starting from 10.0.0-preview.6.25276.106 when performing a Configuration.Bind() to the configuration model.

We observed a change on the benchmark-lab where builder.Configuration was doing a binding to the in-app model representing settings, and without any related changes in aspnetcore repo, value started to being picked from appsettings instead of environment variable.

Basically:

// imagine we have appsettings with `ConnectionString: ....`
// and environment variable `ConnectionString: ...`

var builder = WebApplication.CreateBuilder(args);
var appSettings = new AppSettings();
builder.Configuration.Bind(appSettings);

Console.WriteLine(appSettings.ConnectionString); // gives value from appsettings

if you run such a repro on net9, it will take environment variable value.
The weird part is that builder.Configuration contains env variable value, but appsettings is still binded.

Reproduction Steps

repro: https://github.com/DeagleGross/Baraholka/tree/main/BindingRepro

.net10 output:

.NET Runtime Version: .NET 10.0.0-preview.7.25358.104
.NET Runtime Identifier: win-x64
Process Architecture: X64
OS Architecture: X64
builder.Configuration["ConnectionString"]: environment variable value
AppSettings.ConnectionString: appsettings value

.net9 output:

.NET Runtime Version: .NET 9.0.7
.NET Runtime Identifier: win-x64
Process Architecture: X64
OS Architecture: X64
builder.Configuration["ConnectionString"]: environment variable value
AppSettings.ConnectionString: environment variable value

Expected behavior

Configuration should take value from environment variable

Actual behavior

Configuration takes value from appsettings

Regression?

working version: 10.0.0-preview.5.25265.101
version with regression: 10.0.0-preview.6.25276.106

Known Workarounds

No response

Configuration

No response

Other information

Looks like a regression from Support Null configuration (dotnet/runtime#116677) based on the dates.

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[tarekgh]

This is most likely duplicate of #117444. I am going to submit a fix soon.

[tarekgh]

I confirmed this is the same issue of #117444