CLI tab completion interrupted by first-run banner

[rainersigwald]

Describe the bug

It appears to be possible for the first-run banners to appear mid-tab-completion.

To Reproduce

I believe I had apt update dotnet-sdk-10.0 since the last time I had run a dotnet command on this (WSL) machine. I typed dotnet msbuild par⇥ and got

❯ dotnet msbuild par
Welcome to .NET 10.0!
---------------------
SDK Version: 10.0.103

----------------
Installed an ASP.NET Core HTTPS development certificate.
To trust the certificate, run 'dotnet dev-certs https --trust'
Learn about HTTPS: https://aka.ms/dotnet-https

----------------
Write your first app: https://aka.ms/dotnet-hello-world
Find out what's new: https://aka.ms/dotnet-whats-new
Explore documentation: https://aka.ms/dotnet-docs
Report issues and find source on GitHub: https://github.com/dotnet/core
Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli
--------------------------------------------------------------------------------------
allelbuild.proj

Further technical details

details of dotnet --info

❯ dotnet --info .NET SDK: Version: 10.0.103 Commit: c2435c3e0f Workload version: 10.0.100-manifests.a62d7899 MSBuild version: 18.0.11+c2435c3e0

Runtime Environment:
OS Name: ubuntu
OS Version: 24.04
OS Platform: Linux
RID: ubuntu.24.04-x64
Base Path: /usr/lib/dotnet/sdk/10.0.103/

.NET workloads installed:
There are no installed workloads to display.
Configured to use workload sets when installing new manifests.
No workload sets are installed. Run "dotnet workload restore" to install a workload set.

Host:
Version: 10.0.3
Architecture: x64
Commit: c2435c3e0f

.NET SDKs installed:
9.0.113 [/usr/lib/dotnet/sdk]
10.0.103 [/usr/lib/dotnet/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 9.0.12 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 10.0.3 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 9.0.12 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 10.0.3 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
None

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download

- Ubuntu 24.04.1 in WSL - Tab completions were set up using the older `local completions=("$(dotnet complete "$words")")` mechanism

[baronfel]

Similar to the LLM oriented issues here, the immediate problem is stdout pollution, but the underlying cause is that the CLI doesn't recognize when it is and is not safe to do background checks/work other than the command the user issued. In general, in completions and LLM contexts we should not do background work, and it should be relatively easy to declare/set this.

A few specific actions we should take here:

• all first-run output should emit to stderr
• background operations like workload updates should also emit to stderr
• first-run should be cleanly, entirely disable-able
• we should update tab-completion documentation and generated scripts to disable first-run experiences (via env vars or whatever the correct mechanism is)
• we should audit the actions we take on first-run and see which are actually required and which could be devolved/pushed down to specific impactful commands
  • for example, the global too directory sentinel could be pushed down to the dotnet tool install -g command.
  • for operations that may no longer happen on first run, but may need to explicitly be triggered, we could make hidden/diagnostic commands for them:
  • dotnet nuget migrate
  • dotnet config init dev-cert or similar, etc