Deprecation mechanism for sections or keywords

[robertodr]

Some programs allow different names to be used for the same keywod/section. For example, CONVTHR might be just as valid as CONVERGENCE_THRESHOLD (or something similar). Do we want to allow for this, and if yes how would it look? An alias field accepting a list of aliases?

[bast]

My first reaction was very skeptical.

But after some more thinking: this would be a great mechanism to deprecate keywords. Keyword deprecation is something that we should consider - every code and every input needs that.

[robertodr]

How would deprecation look? A boolean field that emits a warning if set? Or a multiline string? The latter would allow to actually document what to do to avoid the warning...

[bast]

A multi-line string. But perhaps we should open a new issue on deprecation? Since this can be implemented independently of whether there are aliases or not. Although it could go together.

Deprecation is something that many codes simply do not do or do not do well at the frustration of the user who is often 1-2 years behind the developers with inherited input examples. It would also make it easier for developers to change things without being held too tight by backwards compatibility.

[bast]

For the deprecation we need a new field or fields (like "warning" or "error", but we did not conclude on this) which would become function calls in the generated parser and display deprecation warnings or errors to the user.

We postpone this until the rest of the code solidifies a bit.