Showing progress more accurately in burndown chart

Problem to solve

During a sprint, we open many new issues (to break down the work into smaller subtasks), which leads to an almost horizontal line in the burndown chart with the new semantics (see issue #6174 (closed)).

The core problem is that the plotted function looks the same for k items opened and k items closed on one day, independent of k.

Intended users

For all teams that open new issues during a sprint (i.e. for which issue #6174 (closed) is relevant).

Proposal

One solution would be using the old semantics, in which for an issue created in the middle of a milestone, the burndown chart considers it to have been created at the beginning of the milestone (see issue #6174 (closed)).

The optimal solution would be a second function plotted in the chart, which shows the number of closed issues. We would then have one function of open issues (which would in our case be almost horizontal, showing that we open new issues as much as we close issues) and one function for closed issues (which would in our case be almost the identity function f(x)=x, showing our sustainable pace).

Links / references

Issue #6174 (closed)