Fix Geometry service feature reloading the geometry at begin of run
Geometry service checks at each start of a run which geometry configuration the input data was generated with.
If that geometry is different from the currently configured one, it loads the one matching the input data.
This feature is buggy, broken and dangerous.
It is buggy, because it relies just on the name of the geometry to detect whether a new one is needed. Because it assumes the new geometry file is
<GeometryName>.gdml, which is not an advertised requirement. Because it does assume that all the configuration of Geometry service except the detector name and source files are the same. Because it is not able to detect if a new channel mapping algorithm is required by the new geometry.
It is broken, because the requirement of flushing any cached geometry information at run boundaries is not advertised to downstream code.
It is dangerous, because the reload, if completed, may yield erroneous physics results.
This feature has been vocally deprecated. Given the reason above why the feature is broken, I consider it broken beyond repair.
My recommended fix is to leave the code check in
geo::Geometry::preBeginRun(), with the understanding that if the test passes it does not guarantee the consistency of geometry (but if it fails it detects a certainly inconsistent one). As response to a failure of this check, the service should just throw a meaningful exception.
In alternative, this feature should be turned off by default and enabled only when explicitly requested by the user, and in that case it should emit information on the console about the feature being enabled, and about each time the geometry is reloaded (right now it does the latter only indirectly).