bazelbuild/bazel

log download failures when allow_fail is set to true

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#26,336 opened on Jun 18, 2025

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P2help wantedteam-ExternalDepstype: feature request

Description

Description of the feature request:

When a repository_ctx.download fails, it throws an exception when allow_fail=False. However, when it's set to True (as rules_python does) the failure message appears to be swallowed completely. This makes it very difficult to debug what might be failing.

Please provide some method to see the error, even if it's just a DEBUG message.

Which category does this issue belong to?

External Dependency

What underlying problem are you trying to solve with this feature?

Debugging problems with the downloader.

Which operating system are you running Bazel on?

linux

What is the output of bazel info release?

release 8.2.1

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

Contributor guide

Tech stack
java
Domain
build system
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaBazel internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
The issue requests logging download failures when allow fail is true. The change likely needs to be made in Bazel's Java code that implements repository ctx.download, specifically the method that handles the download with allow fail flag. Inspect the source file src/main/java/com/google/devtools/build/lib/bazel/repository/Downloader.java or similar. Ensure that a debug log message is printed when allow fail is true and the download fails. The example from rules python shows usage of the allow fail parameter.