Upgrade to Composer 2

[le0m]

Composer 2 was released last week, this issue is for discussion about its adoption. See here for Composer 2 upgrade guide and possible breaking changes.

Current proposals (see #72 (comment)):

1. have separate images for Composer 1 and 2
2. install both as composer1 and composer2, and create a composer symlink to the latter

Either way, builds are currently failing because hirak/prestissimo is not compatible with composer 2, nor it is needed with it.

[pazion]

I think seperate builds is a bit overkill.
Option 2 with symlinks sounds good.

[fquffio]

Ok, I've started working on this. Turns out having both composer1 and composer2 is a bit of a mess, as there is no obvious way to have them point to separate $COMPOSER_HOME directories. 😶

This wouldn't be a problem if we didn't ship Composer 1 with hirak/prestissimo plugin already installed out of the box. This causes Composer 2 to try to load that plugin as well, and raise a non-fatal warning.

The "cleanest" solution I came up with was to wrap a custom executable around Composer 1 which sets the COMPOSER_HOME environment variable to a different value (COMPOSER_HOME=$COMPOSER1_HOME), and passes everything else down to the original Phar archive:

# Install Composer.
ENV PATH=$PATH:/root/composer2/vendor/bin:/root/composer1/vendor/bin \
  COMPOSER_ALLOW_SUPERUSER=1 \
  COMPOSER_HOME=/root/composer2 \
  COMPOSER1_HOME=/root/composer1
RUN cd /opt \
  # Download installer and check for its integrity.
  && curl -sSL https://getcomposer.org/installer > composer-setup.php \
  && curl -sSL https://composer.github.io/installer.sha384sum > composer-setup.sha384sum \
  && sha384sum --check composer-setup.sha384sum \
  # Install Composer 2 and expose `composer` as a symlink to it.
  && php composer-setup.php --install-dir=/usr/local/bin --filename=composer2 --2 \
  && ln -s /usr/local/bin/composer2 /usr/local/bin/composer \
  # Install Composer 1, make it point to a different `$COMPOSER_HOME` directory than Composer 2, install `hirak/prestissimo` plugin.
  && php composer-setup.php --install-dir=/usr/local/bin --filename=.composer1 --1 \
  && printf "#!/bin/sh\nCOMPOSER_HOME=\$COMPOSER1_HOME\nexec /usr/local/bin/.composer1 \$@" > /usr/local/bin/composer1 \
  && chmod 755 /usr/local/bin/composer1 \
  && composer1 global require hirak/prestissimo \
  # Remove installer files.
  && rm /opt/composer-setup.php /opt/composer-setup.sha384sum

Not actually something I would be proud of in 10 years from now, but sorta works. What do you think?

[le0m]

LGTM
The only problem I see with this solution is that users of this image could get an error if their application is not compatible with Composer 2. We could add a note in the README about composer1/composer2 differentiation.

[fquffio]

Yep, but that's nice to add in any case, even if we would proceed with separate builds, as they would need to change the base image they build upon, and choose the one with Composer 1 instead.

[le0m]

We could've kept the current tags for Composer 1 images and introduce new tags for Composer 2, but that would probably have required more work and the solution you submitted makes more sense to me. I'll add a note in the README.