Composer Dependency Linker and private packages

Summary

Repositories which have composer.json defined render an automatic link to "https://packagist.org/packages/#{name}" and don't take into account that the package might be private and not found on public registry packagist.org.

This is related to gitlab-ce#17476

Steps to reproduce

Create a repo with file composer.json:

{
  "name": "company/package-xyz",
  "description": "Private XYZ package",
  "homepage": "https://example.com/company/package-xyz",
  "type": "library",
  "license": "proprietary",
  "support": {
    "email": "packages@example.com",
    "issues": "https://gitlab.com/company/package-xyz/issues",
    "source": "https://gitlab.com/company/package-xyz/tree/master",
    "docs": "https://gitlab.com/company/package-xyz/tree/master/doc"
  },
  "repositories": [
    {
      "type": "composer",
      "url": "https://composer.example.com/"
    }
  ],
  "require": {
    "php": ">=7.1"
  }
}

Example Project

https://gitlab.com/plehatron/composer-dependecy-linker/blob/master/composer.json

What is the current bug behavior?

Links to https://packagist.org/packages/company/package-xyz

What is the expected correct behavior?

Should link to https://example.com/company/package-xyz

Output of checks

This bug happens on GitLab.com.

Possible fixes

One possible fix might be that the Composer Linker is aware of the homepage property https://getcomposer.org/doc/04-schema.md#homepage and render that link instead of the one pointing to packagist.org.

/label gitlab-ce~2278648