test: enable mypy typing checks for test/components/builders

[ShousenZHANG]

Related Issues

• part of Run typing checks on our test files #10396

Proposed Changes:

test/components/builders/ is not in the repository mypy target, so its test modules are not checked by hatch run test:types. This is the next disjoint increment for #10396, claimed in this comment. It does not overlap the increments in flight: #12343 has extractors/, #12433 has samplers/, #12435 has fetchers/.

The baseline was 25 errors across 2 of the 3 test modules. Nothing here changes what a test asserts:

• 12 attr-defined on __haystack_input__ / __haystack_output__, which the @component decorator attaches at runtime. Ignored the same way the production code reads them in core/pipeline/base.py.
• 8 index / union-attr (4 lines, two errors each) from builder.template[0].text. ChatPromptBuilder.template is typed list[ChatMessage] | str | None, and it is always a list in those tests, so this is narrowed with assert isinstance(builder.template, list) rather than silenced. That resolves both errors per line.
• 2 no-untyped-def on the inline DocumentProducer.run test components, which now declare -> dict[str, list[Document]].
• 1 list-item on template=[ChatMessage.from_user("Hello"), "there world"], a deliberately mixed-type template inside the test that asserts ChatPromptBuilder rejects it. Narrow # type: ignore[list-item], kept on the template= argument itself so the suppression stays attributed to the offending value.

Per AGENTS.md I kept type: ignore to the cases where it is necessary; the index / union-attr group is narrowed with a real assertion instead.

How did you test it?

Red/green against the repository configuration:

• Before: mypy test/components/builders/ reported 25 errors in 2 files.
• After: Success: no issues found in 4 source files.
• Full target: hatch run test:types -> Success: no issues found in 461 source files (up from 457).
• hatch run test:unit test/components/builders/ -> 141 passed, 1 deselected.
• hatch run fmt-check (whole repo) -> clean, 6785 files.

Notes for the reviewer

The only lines that execute anything new are the three assert isinstance(builder.template, list) narrowings, which document an invariant those tests already rely on. Everything else is an annotation or a trailing comment.

Heads-up on this campaign: every increment edits the same single types = "..." line in pyproject.toml, so whichever one lands first leaves the others conflicting. #12433 and #12435 are showing conflicts right now for that reason. Happy to rebase this one whenever it is convenient for you.

No release note: this is test-only, which AGENTS.md excludes from the release-note requirement.

This PR was fully generated with an AI assistant. I have reviewed the changes and run the relevant tests.

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.
• I have documented my code.
• I have added a release note file - not needed here: AGENTS.md scopes the requirement to user-facing changes, and this is test-only.
• I have run pre-commit hooks and fixed any issue.

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[Copilot]

Pull request overview

• Purpose: add test/components/builders/ to the mypy target (hatch run test:types) and resolve the resulting mypy errors via localized test annotations/narrowing, without changing test behavior.

Changes:

• Extend the mypy types target in pyproject.toml to include test/components/builders/.
• Fix mypy errors in builder tests by adding targeted # type: ignore[attr-defined] for runtime-injected __haystack_input__ / __haystack_output__ and by narrowing ChatPromptBuilder.template to list before indexing.
• Add explicit return types for inline @component test components (run(...) -> dict[str, list[Document]]) and a narrow # type: ignore[list-item] for the deliberate mixed-type negative test.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/components/builders/test_prompt_builder.py	Adds typing suppressions for runtime-injected sockets and return type annotations for an inline test component.
test/components/builders/test_chat_prompt_builder.py	Narrows template before indexing, adds socket suppressions, annotates inline test component return type, and scopes a deliberate mixed-type ignore.
pyproject.toml	Includes test/components/builders/ in the mypy types script target.

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[ShousenZHANG]

Heads-up on the red Unit jobs: the failure is pre-existing on main and unrelated to this PR.

The single failing test is test/components/converters/test_pypdf_to_document.py::TestPyPDFToDocument::test_run_detect_paragraphs_to_be_used_in_split_passage, on all three platforms. Everything else passes (1 failed, 6298 passed, 8 skipped).

It reproduces on main itself, not just here — the Tests workflow started failing on main at 29b4171c and has failed on every run since, including ea63575f, which is what this branch is based on:

2026-08-24T16:11  failure  ea63575f   <- base of this branch
2026-08-24T14:04  failure  29b4171c
2026-08-24T10:04  success  7c8ce0f2
2026-08-24T07:40  success  0528f0cb

The assertion diff is a text-extraction change, not a typing one:

- to the public or limited to use within an organization for maintaining its internal knowledge
+ to the public or limited to use within an organization for maintaining its inter nal knowledge

pypdf is emitting a stray space inside "internal", so this looks like it came in with a dependency bump rather than from application code.

This PR touches only test/components/builders/ and one line of pyproject.toml; it doesn't go near the converters. Locally against this branch: hatch run test:types gives Success: no issues found in 461 source files (457 before), hatch run test:unit test/components/builders/ gives 141 passed, and hatch run fmt-check is clean across the repo.

Happy to rebase once main is green again if that's easier for review.

[ShousenZHANG]

Rebased onto main now that #12463 has landed, so the Unit failure I mentioned above is gone. Root cause was exactly that: PyPDF 6.16.2 changed the extracted text, and the converter test's expected string was updated to match.

Verified locally against the same PyPDF version CI uses (6.16.2):

• test/components/converters/test_pypdf_to_document.py -> 15 passed
• full hatch run test:unit -> 6266 passed
• hatch run test:types -> Success: no issues found in 461 source files (457 before this PR)
• hatch run fmt-check -> clean across the repo

The change itself is unchanged by the rebase: one line in the types target plus the typing fixes in test/components/builders/.

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

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Project	Deployment	Actions	Updated (UTC)
haystack-docs	Ready	Preview	Aug 26, 2026 6:49am

[davidsbatista]

looks good, thanks!