verify_pr_lables.py

#!/usr/bin/env python3

import os
import sys
import re
from github import Github

def get_env_var(env_var_name, echo_value=False):
    """Try to get the value from a environmental variable.

    If the values is 'None', then a ValueError exception will
    be thrown.

    Args:
        env_var_name (string): The name of the environmental variable.
        echo_value (bool): Print the resulting value

    Returns:
        string: the value from the environmental variable.
    """
    value=os.environ.get(env_var_name)

    if value == None:
        raise ValueError(f'The environmental variable {env_var_name} is empty!')

    if echo_value:
        print(f"{env_var_name} = {value}")

    return value

# Check if the number of input arguments is correct
if len(sys.argv) < 3:
    print(sys.argv)
    raise ValueError('Invalid number of arguments!')

# Get the GitHub token
token=sys.argv[1]

# Get the list of valid labels
valid_labels=sys.argv[2]

# Post Review
post_review=sys.argv[3]

#Post custom comment
default_comment=f"This pull request does not contain a valid label. Please add one of the following labels: `{valid_labels}`"
post_comment=sys.argv[4] if sys.argv[4] != 'false' else default_comment


print(f'Valid labels are: {valid_labels}')

# Get needed values from the environmental variables
repo_name=get_env_var('GITHUB_REPOSITORY')
github_ref=get_env_var('GITHUB_REF')
github_sha=get_env_var('GITHUB_SHA')
# Create a repository object, using the GitHub token
repo = Github(token).get_repo(repo_name)

# Try to extract the pull request number from the GitHub reference.
try:
    pr_number=int(re.search('refs/pull/([0-9]+)/merge', github_ref).group(1))
    print(f'Pull request number: {pr_number}')
except AttributeError:
    raise ValueError(f'The Pull request number could not be extracted from the GITHUB_REF = {github_ref}')

# Create a pull request object
pr = repo.get_pull(pr_number)

# Get the pull request labels
pr_labels = pr.get_labels()

# This is a list of valid label found in the pull request
pr_valid_labels = []

# Check which of the label in the pull request, are in the
# list of valid labels
for label in pr_labels:
    if label.name in valid_labels:
        pr_valid_labels.append(label.name)

# Check if there were at least one valid label
# Note: In both cases we exit without an error code and let the check to succeed. This is because GitHub
# workflow will create different checks for different trigger conditions. So, adding a missing label won't
# clear the initial failed check during the PR creation, for example.
# Instead, we will create a pull request review, marked with 'REQUEST_CHANGES' when no valid label was found.
# This will prevent merging the pull request until a valid label is added, which will trigger this check again
# and will create a new pull request review, but in this case marked as 'APPROVE'

if len(pr_valid_labels):
    # If there were valid labels, then create a pull request request review, approving it
    print(f'Success! This pull request contains the following valid labels: {pr_valid_labels}')
    repo.get_commit(sha=github_sha).create_status(
        state="success",
        target_url="https://amazon.com",
        description="This pull request contains the following valid labels",
        context="ci/FooCI"
    )
    if post_review == "true":
        pr.create_review(event = 'APPROVE')
else:
    # If there were not valid labels, then create a pull request review, requesting changes
    print(f'Error! This pull request does not contain any of the valid labels: {valid_labels}')
    repo.get_commit(sha=github_sha).create_status(
        state="failure",
        target_url="https://amazon.com",
        description="This pull request does not contain any of the valid labels",
        context="ci/FooCI"
    )
    if post_review == "true":
        pr.create_review(body = 'This pull request does not contain a valid label. '
                            f'{post_comment}',
                     event = 'REQUEST_CHANGES')