In Java, uv (at least uv) logs info messages as errors

[tinevez]

Even when successful, info messages are logged as errors:

[INFO ] Loading VTK...
[INFO ] Icy v3.0.0-a.5 started
[INFO ] VTK 9.3.1 loaded
[ERROR] Using CPython 3.10.10 interpreter at: /Users/tinevez/mambaforge/bin/python3
[ERROR] Creating virtual environment at: plugins_tinevez_appose_cellpose_cellpose3_0_1_icy
[ERROR] Activate with: source plugins_tinevez_appose_cellpose_cellpose3_0_1_icy/bin/activate
[ERROR] Using Python 3.10.10 environment at: plugins_tinevez_appose_cellpose_cellpose3_0_1_icy
[ERROR] Resolved 10 packages in 23ms
[ERROR] Installed 10 packages in 38ms
[ERROR] + appose==0.11.0
[ERROR] + imageio==2.37.2
[ERROR] + lazy-loader==0.4
[ERROR] + networkx==3.4.2
[ERROR] + numpy==2.2.6
[ERROR] + packaging==26.0
[ERROR] + pillow==12.1.1
[ERROR] + scikit-image==0.25.2
[ERROR] + scipy==1.15.3
[ERROR] + tifffile==2025.5.10
[INFO ] Starting task
[INFO ] Task started
[INFO ] null
[INFO ] Hello from Python!

[tinevez]

It is a minor issue of course, but it could really improve the Icy integration:

[ctrueden]

This is how command-line tools are typically designed, emitting status updates on stderr, and "user-requested" program output on stdout. For example:

$ uv tree
Resolved 2 packages in 0.85ms
t v0.1.0
└── cowsay v6.1

$ uv tree >/dev/null
Resolved 2 packages in 0.77ms

$ uv tree 2>/dev/null
t v0.1.0
└── cowsay v6.1

Above, we that "Resolved 2 packages in 0.85ms" is sent to stderr, while the actual dependency tree is sent to stdout.

So the question is: how should Appose respond to such behavior?

The current approach is that we simply pass along output from the build tool—you can subscribeOutput to the stdout, and subscribeError to the stderr, and do what you like with the content.

So one simple solution would be to change your Appose code in Icy to do something different with the lines being fed to your subscriber callbacks. If something actually goes wrong with the build, a BuildException will be thrown; otherwise, you could assume that content being fed to the subscribeError subscriber is not actually an error per se, merely the typical status update feed from the build tool as usual.

Tangentially: I don't love that Appose's builder implementations currently feed the output directly from the tools like this—I would rather the subscribeProgress be actually useful and feed real current/maximum values with meaningful messages, rather than the tool-specific arcane gobbledygook currently emitted. I did investigate how to receive more structured output from the tools, but the ability to output more machine-readable content from them is not there yet—although at least for uv, it is planned. Once this feature exists, we could improve Appose to run uv always in this machine-readable mode, consume the JSON as it emerges, and transform it into nicer progress reporting.