fix(tf): find external protobuf for TensorFlow 2.21

[njzjz-bot]

Summary

Adapt the conda-forge TensorFlow 2.21 external-Protobuf fix for upstream use.

• Find the external Protobuf package when TensorFlow does not expose protobuf as a direct runtime dependency.
• Preserve an exact protobuf library discovered from the TensorFlow runtime dependencies.
• Use that library installation prefix to guide the header lookup, then restore any caller-provided Protobuf root.

Validation

• Focused CMake configure: preserved a versioned runtime-discovered protobuf library even when a different protobuf prefix was globally searchable.
• Focused CMake configure: found protobuf normally when the TensorFlow runtime dependency scan produced no protobuf library.
• cmake-format check passed for source/cmake/Findtensorflow.cmake.
• ruff check . passed.
• ruff format . left 1913 files unchanged.

Repository CI does not exercise the external-header branch because its pip TensorFlow packages bundle google/protobuf/type.pb.h. The focused CMake configurations above validate the changed lookup behavior directly.

Coding agent: Codex
Codex version: codex-cli 0.149.0
Model: gpt-5.6-sol
Reasoning effort: xhigh

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: cd6918f7-87ee-4254-b10a-1373e0d51f25

📥 Commits

Reviewing files that changed from the base of the PR and between 2093090 and 72f40f4.

📒 Files selected for processing (1)

• source/cmake/Findtensorflow.cmake

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📝 Walkthrough

Walkthrough

The TensorFlow CMake module now preserves the runtime-discovered Protobuf library, uses its installation prefix for temporary package discovery, restores the original Protobuf_ROOT, and assigns the discovered Protobuf include and library variables.

Changes

TensorFlow discovery

Layer / File(s)	Summary
Require Protobuf package resolution source/cmake/Findtensorflow.cmake	When TensorFlow provides a runtime Protobuf library, the module temporarily sets Protobuf_ROOT from its installation prefix. It requires Protobuf discovery, restores the previous root value, and assigns TensorFlow’s Protobuf variables from Protobuf_INCLUDE_DIRS and Protobuf_LIBRARIES.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 72f40

This localized build-dependency discovery change improves TensorFlow 2.21 protobuf handling without introducing a supported merge-blocking risk; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (1 skipped: 1 unsupported.)
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the TensorFlow 2.21 Protobuf discovery fix, which matches the main change.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.84%. Comparing base (8cfd46e) to head (72f40f4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5986      +/-   ##
==========================================
- Coverage   79.10%   78.84%   -0.26%     
==========================================
  Files        1105     1105              
  Lines      130981   130981              
  Branches     4771     4765       -6     
==========================================
- Hits       103609   103272     -337     
- Misses      25686    26025     +339     
+ Partials     1686     1684       -2     

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[wanghan-iapcm]

Non-blocking. The fix is sound for the environment it came from, and I confirmed the backport is byte-identical to the feedstock patch. Two notes and one fact about coverage.

Worth stating plainly: no CI job executes these lines. The branch is only entered when google/protobuf/type.pb.h is absent from the TensorFlow tree, and CI installs TensorFlow from pip wheels, which bundle that header (checked on a local pip TensorFlow: .../tensorflow/include/google/protobuf/type.pb.h is present, and it is exactly the sentinel find_path looks for at line 224). So the green checks on this PR say nothing about the change, and "Full build is left to upstream CI" does not hold for this path, because this repository's CI does not cover it. That is not a reason to block -- there is no reasonable unit test for a find-module branch like this, and adding a conda-forge-TensorFlow build job is far more than this PR should carry -- but it is worth being explicit that the change ships unexercised.

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[njzjz]

The review summary coverage note is addressed as well: the PR description now explicitly states that repository CI does not execute the external-header branch and removes the previous claim that a full build was left to upstream CI. It documents the focused CMake configurations used to validate both the pinned runtime-library path and the TensorFlow 2.21 fallback path.

The inline threads have been addressed and resolved, and reviews have been re-requested.

Coding agent: Codex
Codex version: codex-cli 0.149.0
Model: gpt-5.6-sol
Reasoning effort: xhigh