What is a regression?

[Jason Merrill]

I think that the release process for recent releases has given undue 
priority to bugs marked as regressions.  I agree that it's important for 
things that worked in the previous release to keep working in the new 
release.  But the regression tag is used for much more trivial things.

For instance, Bug 32252 is an ice-on-valid bug in a new C++ feature, 
variadic templates.  But since 4.2 gave a syntax error instead of an 
ICE, this gets marked as a regression.

This seems wrong to me.  We should only use the regression tag for 
things that worked properly in the previous release and fail in the new 
release.  A change from rejects-valid to ice-on-valid is an extremely 
low priority for me, and should not affect the release schedule.  I 
would like to remove the regression tag entirely from such bugs.

Similarly, bugs marked as 4.1/4.2/4.3 regression don't seem like a high 
priority to me.  If a bug wasn't a blocker for 4.2, it shouldn't be a 
blocker for 4.3.  It makes sense to give such a bug a higher priority 
than it would normally (say, one point higher), but it seems to me that 
only regressions relative to the previous release series should actually 
be considered for release timing.

Incidentally, how are priorities assigned to bugs?  I don't see any 
guidelines on the website.

Jason