[WIP] chore(bigframes): add specific build script for doctest to restrict execution

[chalmerlowe]

Warning

This is a work in progress. Do not review until invited.

Creates a build script: packages/bigframes/scripts/run_doctest.sh. This script checks if bigframes has any changes (or if it's a continuous build) before runnin' the cleanup doctest sessions. This will prevent it from running when other packages are modified and failing the build.

Updates the Kokoro config: .kokoro/presubmit/presubmit-doctest-bigframes.cfg to set TRAMPOLINE_BUILD_FILE to point to the new script.

[gemini-code-assist]

Code Review

This pull request introduces a new presubmit configuration and a bash script, run_doctest.sh, to automate doctests for the bigframes package. The script detects changes using git diff and executes nox sessions accordingly. The review feedback identifies several critical improvements for the bash script: correcting the nox command syntax to handle multiple sessions properly, adding necessary quoting to handle file paths with spaces, and implementing checks for Kokoro environment variables to prevent syntax errors in non-pull request builds.

[gemini-code-assist]

The NOX_SESSION variable contains multiple session names separated by a space. When passed to nox -s inside double quotes, Nox treats the entire string as a single session name (e.g., "cleanup doctest"), which will fail if no such session exists. Additionally, NOX_SESSION is not a standard environment variable recognized by Nox; sessions should be specified via command-line arguments.

Suggested change

	export NOX_SESSION="cleanup doctest"
	cd "${package_path}"
	python3 -m nox -s "${NOX_SESSION}"
	cd "${package_path}"
	python3 -m nox -s cleanup -s doctest

[gemini-code-assist]

The argument to realpath should be quoted to correctly handle directory paths that may contain spaces.

Suggested change

	export PROJECT_ROOT=$(realpath $(dirname "${BASH_SOURCE[0]}")/../../..)
	export PROJECT_ROOT=$(realpath "$(dirname "${BASH_SOURCE[0]}")/../../..")

[gemini-code-assist]

The output of realpath . should be quoted to ensure the command works correctly if the current directory path contains spaces.

Suggested change

	git config --global --add safe.directory $(realpath .)
	git config --global --add safe.directory "$(realpath .)"

[gemini-code-assist]

The git diff command relies on environment variables that are typically only available in pull request builds. In other contexts (like continuous builds), these variables will be empty, leading to a git syntax error. While set +e prevents the script from terminating, it's cleaner to check for the presence of these variables. Additionally, the file path should be quoted.

Suggested change

	echo "checking changes with 'git diff ${KOKORO_GITHUB_PULL_REQUEST_TARGET_BRANCH}...${KOKORO_GITHUB_PULL_REQUEST_COMMIT} -- ${files_to_check}'"
	set +e
	package_modified=$(git diff "${KOKORO_GITHUB_PULL_REQUEST_TARGET_BRANCH}...${KOKORO_GITHUB_PULL_REQUEST_COMMIT}" -- ${files_to_check} | wc -l)
	set -e
	if [[ -n "${KOKORO_GITHUB_PULL_REQUEST_TARGET_BRANCH}" && -n "${KOKORO_GITHUB_PULL_REQUEST_COMMIT}" ]]; then
	echo "checking changes with 'git diff ${KOKORO_GITHUB_PULL_REQUEST_TARGET_BRANCH}...${KOKORO_GITHUB_PULL_REQUEST_COMMIT} -- ${files_to_check}'"
	set +e
	package_modified=$(git diff "${KOKORO_GITHUB_PULL_REQUEST_TARGET_BRANCH}...${KOKORO_GITHUB_PULL_REQUEST_COMMIT}" -- "${files_to_check}" | wc -l)
	set -e
	else
	package_modified=0
	fi

[parthea]

Switching to draft until checks are green

------------------------------------------------------------
Running doctest for: bigframes
------------------------------------------------------------
nox > Error while collecting sessions.
nox > Sessions not found: cleanup doctest

I just noticed that the test is skipped in the output

nox > Running session doctest
nox > Creating virtual environment (virtualenv) using python3.12 in .nox/doctest
nox > Session doctest skipped: Temporary skip to enable a PR merge. Remove skip as part of closing https://github.com/googleapis/google-cloud-python/issues/16489.
cleanup