Installation fails when Generating optimized autoload files

Edit: these warnings are NOT FATAL. See my comment below!

When trying to install Shopware 6.1 community edition on a shared host, installation stops with the warning.

MatrixStatsAggregation.php does not comply with psr-4 autoloading standard

System information:

FreeBSD 12.1-RELEASE-p2 GENERIC
PHP 7.2.30 (cli) (built: Apr 22 2020 15:03:18) ( NTS )
Zend Engine v3.2.0
Composer version 1.10.0 2020-03-10 14:08:05

What I did:

git clone --branch=6.1 https://github.com/shopware/production shopware
cd shopware/
composer install

Installation proceeded successfully until after the guzzlehttp deprecation warning, when it starts to

Generating optimized autoload files

where it stops with this error message:

Deprecation Notice: Class ONGR\ElasticsearchDSL\Aggregation\Matrix\MaxAggregation located in ./vendor/ongr/elasticsearch-dsl/src/Aggregation/Matrix/MatrixStatsAggregation.php does not comply with psr-4 autoloading standard. It will not autoload anymore in Composer v2.0. in phar:///usr/local/bin/composer.phar/src/Composer/Autoload/ClassMapGenerator.php:185
Deprecation Notice: Class HTMLPurifier_Language_en_x_test located in ./vendor/ezyang/htmlpurifier/library/HTMLPurifier/Language/classes/en-x-test.php does not comply with psr-0 autoloading standard. It will not autoload anymore in Composer v2.0. in phar:///usr/local/bin/composer.phar/src/Composer/Autoload/ClassMapGenerator.php:185
Killed

 

This is a false positive. There must have been another reason for the killed process.

The warnings are not fatal at all.

A second try of composer install got past these warnings without a problem.