Magento2: Cannot uninstall 3th party module. Magento reads location of composer.json wrong

[PascalBrouwers]

Preconditions

1. Magento 2.1.x
2. PHP 7.0.14
3. MySQL 5.7.16

Steps to reproduce

1. Have a custom module with the following structure.
2. composer.json
3. registration.php
4. src
5. in registration.php have the dir as: __DIR__.'/src'
6. in composer.json have psr-4 as: "Vendor\\Module\\": "src/"
7. have some installSchema, installData file in src\Setup
8. have a Uninstall file in src\Setup
9. run: bin/magento module:uninstall Vendor_Module --remove-data

Expected result

1. It should properly find the composer.json file and uninstall the module

Actual result

1. Exits with error: Vendor_Module is not an installed composer package

But if you add a composer.json file to src/ then it will uninstall the module, but this is not where the composer.json file should be for 3rd modules.

Related issues:
https://github.com/magento/magento2/issues/7064
https://github.com/magento/magento2/issues/3290

[PascalBrouwers]

You can look in Magento\Framework\Module\Dir->getComposerJsonFiles() for the problem

[speedupmate]

the conflict comes from a method inside

Magento\Framework\Module\Dir\Reader.php

where

private function getFiles($filename, $subDir = '')

where

$file = $moduleSubDir . '/' . $filename;

is looking composer.json from path defined in composer.json itself as psr-4 (and not using the composer.json that was used to install the module )

[magento-engcom-team]

@PascalBrouwers, thank you for your report.
We've created internal ticket(s) MAGETWO-81455 to track progress on the issue.