Tables not migrated if plugins not explicitly enabled in [components] section

[Ryan J Ollos]

The issue I experienced is that none of the plugin tables were being migrated for an installation. I discovered that the plugins had been installed in the plugins directory and were not explicitly enabled in trac.ini, instead were implicitly enabled (TracPlugins#Plugindiscovery).

It looks like plugins must be explicitly enabled for the tables to be migrated: tracmigrateplugin/0.12/tracmigrate/admin.py@14655:113,117-118#L97​.

The tables were migrated after explicitly enabling the plugin components. This is an in-place migration.

Maybe no code change is needed though, rather just a note added to the documentation.

Even if we only document the caveat for the plugin, when adding the feature to Trac (​trac:#12299) maybe we should consider a more robust approach. I have never really liked that plugins are implicitly enabled when added to the plugins directory. Maybe that behavior should be changed for Trac 1.2 and require that all plugins be explicitly enabled? I hesitate to suggest that though, because unless we can automatically populate the components section on upgrade, then we are likely to see a lot of issues reported by users due to the backward-incompatible change.