Cannot downgrade to version 1 if using PEAR

[fulldecent]

In the documentation multiple times it is advertised: trying Composer 2 is easy, and you can quickly go back if it doesn't work. (One example is at https://blog.packagist.com/deprecating-composer-1-support/)

I tried it and found that going back is difficult if you are using PEAR.

Upgrading to try is easy:

php composer.phar self-update --2 
Updating to version 2.1.5 (2 channel).
   Downloading (100%)         
Use composer self-update --rollback to return to version 1.10.8

Downgrading failed

php composer.phar self-update --1

                                                          
  [RuntimeException]                                      
  The PEAR repository has been removed from Composer 2.0  
                                                          

It also failed using the above instructions shown when I upgraded:

php composer.phar self-update --rollback

                                                          
  [RuntimeException]                                      
  The PEAR repository has been removed from Composer 2.0  
                                                          

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Intuitively I even expected upgrading might be a problem so I ran cp composer.* ~ before upgrading.

But reverting with mkdir tmp; mv composer.* tmp; cp ~/composer.* . did not work -- somehow the result is I am still running version 2.

End result is: can't upgrade, can't downgrade, some magic is preventing me from using composer at all.

[stof]

well, as your phar is named composer.phar and you use composer.* in your mv and cp commands, you are also moving the phar, not only the config files.

[Seldaek]

As a workaround, you can add --version 1.10.22 to the setup instructions to install a specific version, i.e.:

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 --version 1.10.22
php -r "unlink('composer-setup.php');"

Or simply download a phar file you want for any version on https://getcomposer.org/download/

That said, it's a good point that self-update should not break if the composer.json is not supported. I'll have a look at what is causing that.