Source

File: wp-admin/includes/class-wp-automatic-updater.php

public function is_vcs_checkout( $context ) {
		$context_dirs = array( untrailingslashit( $context ) );
		if ( ABSPATH !== $context ) {
			$context_dirs[] = untrailingslashit( ABSPATH );
		}

		$vcs_dirs   = array( '.svn', '.git', '.hg', '.bzr' );
		$check_dirs = array();

		foreach ( $context_dirs as $context_dir ) {
			// Walk up from $context_dir to the root.
			do {
				$check_dirs[] = $context_dir;

				// Once we've hit '/' or 'C:\', we need to stop. dirname will keep returning the input here.
				if ( dirname( $context_dir ) === $context_dir ) {
					break;
				}

				// Continue one level at a time.
			} while ( $context_dir = dirname( $context_dir ) );
		}

		$check_dirs = array_unique( $check_dirs );

		// Search all directories we've found for evidence of version control.
		foreach ( $vcs_dirs as $vcs_dir ) {
			foreach ( $check_dirs as $check_dir ) {
				$checkout = @is_dir( rtrim( $check_dir, '\\/' ) . "/$vcs_dir" );
				if ( $checkout ) {
					break 2;
				}
			}
		}

		/**
		 * Filters whether the automatic updater should consider a filesystem
		 * location to be potentially managed by a version control system.
		 *
		 * @since 3.7.0
		 *
		 * @param bool $checkout  Whether a VCS checkout was discovered at $context
		 *                        or ABSPATH, or anywhere higher.
		 * @param string $context The filesystem context (a path) against which
		 *                        filesystem status should be checked.
		 */
		return apply_filters( 'automatic_updates_is_vcs_checkout', $checkout, $context );
	}