Change in argument handling in dotnet run between 9.0.103 and 9.0.200

[mareklinka]

Describe the bug

There seems to be a regression/change of behavior in how dotnet run handles command line arguments.

I have an ASP.NET core application targeting .NET 9. We have migrated from SDK 9.0.103 to 9.0.200 last week and immediately started having issues with our test pipelines. I tracked the issue to the behavior of dotnet run.

Our command line: dotnet run --environment UiTests --urls https://localhost:7139

In 9.0.103, this produced the following output (parts omitted for brevity):

Using launch settings from [path]\launchSettings.json...
Building...
[11:57:51 INF] User profile is available. Using '[user profile]\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
[11:57:52 WRN] The ASP.NET Core developer certificate is not trusted. For information about trusting the ASP.NET Core developer certificate, see https://aka.ms/aspnet/https-trust-dev-cert
[11:57:52 INF] Now listening on: https://localhost:7139
[11:57:52 INF] [app] application 'Started'
[11:57:52 INF] Application started. Press Ctrl+C to shut down.
[11:57:52 INF] Hosting environment: UiTests
[11:57:52 INF] Content root path: [root path]

In 9.0.200, this has changed:

Using launch settings from [path]\launchSettings.json...
Building...
[11:59:36 INF] User profile is available. Using '[user profile]\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
[11:59:37 WRN] The ASP.NET Core developer certificate is not trusted. For information about trusting the ASP.NET Core developer certificate, see https://aka.ms/aspnet/https-trust-dev-cert
[11:59:37 INF] Now listening on: https://localhost:7139
[11:59:37 INF] [app] application 'Started'
[11:59:37 INF] Application started. Press Ctrl+C to shut down.
[11:59:37 INF] Hosting environment: Development
[11:59:37 INF] Content root path: [root path]

Note the difference in Hosting environment. It looks like in 9.0.200, the --environment was not passed to the application being run.

If I change the command line to dotnet run -- --environment UiTests --urls https://localhost:7139, we get the expected output:

Using launch settings from [path]\launchSettings.json...
Building...
[12:02:14 INF] User profile is available. Using '[user profile]\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
[12:02:14 WRN] The ASP.NET Core developer certificate is not trusted. For information about trusting the ASP.NET Core developer certificate, see https://aka.ms/aspnet/https-trust-dev-cert
[12:02:14 INF] Now listening on: https://localhost:7139
[12:02:14 INF] [app] application 'Started'
[12:02:14 INF] Application started. Press Ctrl+C to shut down.
[12:02:14 INF] Hosting environment: UiTests
[12:02:14 INF] Content root path: [root path]

I wasn't able to find any documentation about this change, in fact, this documentation still contains the old format without the -- separator. Is this change expected? If so, I think this is a breaking change that should be documented somewhere. If not, I guess this is a bug report.