Two things may largely eliminate the need for parallel branches.
1. Do infrastructure changes and whole tree wide refactoring etc. in a
compatible manner with a brief but nonzero transition period.
2. Insert a second merge window right after the usual merge window for
changes which cannot be well done with a transition period.
(I probably missed a number of points why these two things are not
always feasible, because I am just a downstream person.)
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Stefan Richter
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http://arcgraph.de/sr/
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