BLT 12.x, Acquia Pipelines, and Composer 2

[mikemadison13]

Describe the bug
BLT requires Composer 2 as of 12.5. See https://docs.acquia.com/resource/using-composer/#blt. However, Acquia Pipelines does not yet support composer 2. As a result, you may see errors like:

 Problem 1
    - Installation request for acquia/blt 12.8.0 -> satisfiable by acquia/blt[12.8.0].
    - acquia/blt 12.8.0 requires composer-plugin-api ^2.0 -> no matching package found.

The solution for this is to temporarily pin your BLT installation to 12.4. https://docs.acquia.com/resource/using-composer/ provides more information on the Acquia Pipelines timeline.

[mikemadison13]

I've done a basic POC over on the GovCon site to update the Pipelines script there to use Composer 2. See Drupal4Gov/Drupal-GovCon-2017#937.

A few caveats:

• i'm manually installing composer 2 during the build and aliasing it (not actually updating the container)
• i had to add a .gitignore rule for composer.phar before blt would complete a deployment.

TLDR add this to your pipelines script section:

- php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
- php -r "if (hash_file('sha384', 'composer-setup.php') === '756890a4488ce9024fc62c56153228907f1545c228516cbf63f885e036d37e9a59d27d63f46af1d4d07ee0f76181c7d3') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
- php composer-setup.php
- php -r "unlink('composer-setup.php');"
- alias composer="php -d memory_limit=-1 /mnt/tmp/local.prod/source/composer.phar"

and throw this at the end of your project's .gitignore

composer.phar