feat: Enable components to automatically accept multiple connections if their input type is list

[sjrl]

Related Issues

• fixes https://github.com/deepset-ai/haystack-private/issues/241

Proposed Changes:

Natively support connecting multiple outputs directly to another component without needing the user to define a Joiner component.

For example, a user may want to connect multiple output edges of the FileTypeRouter to all go to the same converter (e.g. ImageConverter). Before you would have to define a ListJoiner as an in-between component. The changes introduced in this PR would allow you to directly connect all outputs from the FileTypeRouter to the ImageConverter.

How did you test it?

• Added complex pipeline run test based off an existing one.

Notes for the reviewer

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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1 Skipped Deployment

Project	Deployment	Review	Updated (UTC)
haystack-docs	Ignored	Preview	Jan 27, 2026 10:26am

[coveralls]

Pull Request Test Coverage Report for Build 21361994530

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 58 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.02%) to 92.431%

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Files with Coverage Reduction	New Missed Lines	%
core/component/types.py	3	92.68%
core/pipeline/pipeline.py	3	93.16%
core/pipeline/base.py	52	86.68%

Totals
Change from base Build 21361849247:	-0.02%
Covered Lines:	14763
Relevant Lines:	15972

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💛 - Coveralls