feat(firestore): support let stage

[Linchin]

TODO:

• verify docstring
• add variable_field_reference

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces the let pipeline stage to the Firestore client library, enabling users to define and compute variables within a pipeline. These variables can then be referenced in subsequent stages, significantly enhancing the flexibility and expressiveness of data processing pipelines by allowing intermediate calculations and named values.

Highlights

• New 'let' Pipeline Stage: Introduced a new let pipeline stage that allows users to define and compute variables within a Firestore pipeline, enhancing data manipulation capabilities.
• Core Implementation: Implemented the Let class in pipeline_stages.py to handle the internal logic and protobuf serialization for the new let stage.
• Comprehensive Testing: Added both system-level (YAML) and unit tests to validate the functionality, correct argument handling, and protobuf conversion of the let pipeline stage.

Changelog

• packages/google-cloud-firestore/google/cloud/firestore_v1/base_pipeline.py
  • Added the let method to the _BasePipeline class, allowing users to define variables for subsequent pipeline stages.
• packages/google-cloud-firestore/google/cloud/firestore_v1/pipeline_stages.py
  • Implemented a new Let class, inheriting from Stage, to represent the 'let' pipeline stage internally.
  • Added _pb_args method to the Let class for converting defined variables into the appropriate protobuf format.
• packages/google-cloud-firestore/tests/system/pipeline_e2e/general.yaml
  • Included a new system test case (testLetStage) to verify the functionality and correct proto generation of the let pipeline stage.
• packages/google-cloud-firestore/tests/unit/v1/test_pipeline.py
  • Updated the test_pipeline_methods function to correctly handle keyword arguments for the newly introduced let pipeline stage.
• packages/google-cloud-firestore/tests/unit/v1/test_pipeline_stages.py
  • Added comprehensive unit tests for the Let class, covering its constructor, string representation (__repr__), and protobuf conversion (_to_pb).

Activity

• The author has noted two outstanding TODOs: verifying docstrings and adding variable_field_reference, indicating planned follow-up work for this feature.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request introduces support for the let stage in Firestore pipelines, which is a great feature. The implementation looks solid, with new classes for the stage, methods on the pipeline builder, and thorough unit and system tests. I have a couple of suggestions: one to improve the clarity of the docstring for the new let method, and another to ensure deterministic behavior by sorting variables in the Let stage, following repository best practices.

[gemini-code-assist]

The docstring mentions Variable.of("rating_plus_one"), but the Variable class or a way to reference variables doesn't seem to be part of this pull request, as indicated by the TODO item add variable_field_reference. To avoid confusion and documenting a feature that is not yet available, it would be better to remove this line. The preceding sentences already explain that variables can be used in subsequent stages.

[gemini-code-assist]

To ensure deterministic output for __repr__ and protobuf serialization, it's a good practice to sort the variables. This aligns with the general principle of producing predictable output, which is especially helpful for testing. You can sort the variables by key when they are assigned in the constructor.

Suggested change

	self.variables = variables
	self.variables = dict(sorted(variables.items()))

References

1. To ensure dictionary keys remain sorted without manual effort, programmatically sort the dictionary before returning it (e.g., using dict(sorted(metadata.items()))) instead of relying on manual ordering in the code.