feat(firestore): support array functions

[Linchin]

Supports the following:

• array_first
• array_last
• array_first_n
• array_last_n
• array_maximum
• array_maximum_n
• array_minimum
• array_minimum_n
• array_slice
• array_index_of
• array_index_of_all
• array_transform (need to check for ref impl when it's ready - docstring, and sep methods or not)
• array_filter (need to check for ref impl when it's ready - docstring, and sep methods or not)

[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 enhances the Firestore client library by integrating new array manipulation functions directly into pipeline expressions. This provides developers with more powerful and convenient ways to query and transform data within array fields, improving data processing capabilities without requiring client-side array handling.

Highlights

• New Array Functions: Introduced array_first, array_last, array_first_n, and array_last_n to the Firestore pipeline expressions, allowing users to extract specific elements or sub-arrays from array fields.

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[gemini-code-assist]

Code Review

This pull request adds support for array_first, array_last, array_first_n, and array_last_n functions in Firestore pipelines. The implementation and system tests look good. However, I found issues in the unit tests for array_first_n and array_last_n where the parameter order is asserted incorrectly, leading to internally inconsistent tests. I've provided suggestions to fix these tests.

[Linchin]

/gemini review

[gemini-code-assist]

Code Review

This pull request adds support for a number of new array functions in Firestore pipelines. The implementation looks mostly good, but there are a few areas for improvement.

There are some inconsistencies in the naming of the generated functions (e.g., maximum vs array_maximum) which should be standardized. The e2e tests for these functions are also missing assert_proto blocks to verify the generated output.

Additionally, there are some minor issues with docstrings and redundant code that can be cleaned up. The signature for array_transform is also a bit confusing and could be made clearer.

Overall, a solid addition with a few refinements needed.

[gemini-code-assist]

The method signature for array_transform is (self, element_alias: str, body: "Expression", index_alias: str | None = None). However, the implementation and the expected backend protocol place the body argument last in the argument list sent to the backend. This discrepancy can be confusing and lead to incorrect usage.

To improve clarity and prevent misuse, consider making index_alias a keyword-only argument. This enforces that it's passed by name and makes the signature less ambiguous.

    def array_transform(
        self, element_alias: str, body: "Expression", *, index_alias: str | None = None
    ) -> "Expression":

[daniel-sanche]

This is probably a good suggestion

[Linchin]

This method is removed for the purpose of this PR because we are still waiting for reference implementation.

[gemini-code-assist]

The body parameter is already typed as Expression. Calling _cast_to_expr_or_convert_to_constant on it is redundant, as unit tests suggest this function is a no-op for Expression instances. You can append body directly to the args list for clarity.

This also applies to array_filter on line 1733.

        args.append(body)

[Linchin]

irrelevant since this part is removed

[gemini-code-assist]

The docstring for array_filter is inconsistent with the other new functions in this PR.

• It's missing an Example: section.
• The Returns: description is not as user-friendly as the others.

Please update it for consistency. For example:

        """
        Takes an array and returns a new array containing only the elements for which
        the given boolean expression evaluates to True.

        Example:
            >>> # Filter for numbers greater than 5
            >>> Field.of("numbers").array_filter("num", Field.of("num").greater_than(5))

        Args:
           element_alias: Element variable name.
           body: Boolean expression applied to each element.

        Returns:
            A new `Expression` representing the filtered array.
        """

[Linchin]

irrelevant since this part is removed

[daniel-sanche]

this should be array_maximum. You can use infix_name_override for this

[Linchin]

Thanks, I have fixed array_maximum, array_maximum_n, array_minimum, array_minimum_n.

[daniel-sanche]

It looks like Gemini caught a typo and some other small suggestions. Other than that, LGTM