I installed pear/archive_tar to work with Phing, which I installed with Composer. However, I received this error:
BUILD FAILED
exception 'BuildException' with message 'Error reading project file [wrapped: You must have installed the PEAR Archive_Tar class in order to use TarTask.]' in vendor/phing/phing/classes/phing/parser/ProjectConfigurator.php:197
I added the PEAR repository to Composer and updated, but it still did not work.
The second half of this question branched off here.