Apparently the latest composer version (cb8587cdade3cdbe00b8d6d2488458a2b6c0a592) has changed the signature of the whatProvides method:
[ErrorException] Declaration of Fxp\Composer\AssetPlugin\Repository\AbstractAssetsRepository::whatProvides() should be compatible with Composer\Repository\ComposerRepository::whatProvides(Composer\DependencyResolver\Pool $pool, $name, $bypassFilters = false)
Apparently the latest composer version (cb8587cdade3cdbe00b8d6d2488458a2b6c0a592) has changed the signature of the whatProvides method:
[ErrorException] Declaration of Fxp\Composer\AssetPlugin\Repository\AbstractAssetsRepository::whatProvides() should be compatible with Composer\Repository\ComposerRepository::whatProvides(Composer\DependencyResolver\Pool $pool, $name, $bypassFilters = false)