unbalanced if-eqns are not detected

[anonymous]

Following model is accepted even it is not really balanced. Also the result is really odd.

model ifeqns
  Real x(start=-1);
  Real y1,y2;
equation 
der(x) = sin(time);

if x > 0 then
  y1 = x;
  y2 = 2*y1*x;
elseif x > 0.75 then
  y2 = 2.0;
else
  y2 = 2*x;
  y1 = 3*x;
end if;

end ifeqns;

[lochel]

Well, this model is not really accepted. It just passes the frontend, however the issue is detected later on and even the error message is quite helpful:

[<interactive>:8:1-16:7:writable] Error: If-equation with conditions that are not parameter expressions must have the same number of equations in each branch, equation count is {2,1,2} for each respective branch:
1 : y2 = 2.0 * y1 * x
2 : y1 = x
1 : y2 = 2.0
1 : y1 = 3.0 * x
2 : y2 = 2.0 * x

There are two issues to fix:

• Don’t continue compilation when an error message is triggered.
• Catch this already in the frontend.

[lochel]

The compilation continuous because of badly nested matchcontinue statements …

[sjoelund.se]

​PR1957 moves this check to the BackendDAECreate part of the compiler, but I am unsure if there might be some models with parameter conditions that are evaluated in the backend at a later stage that would stop working with this change (in that case, there would need to be a check just before code generation).

[sjoelund.se]

@lochel - it seems my fears are true. Should we move the check for unbalanced if-equations to the simcode or should we evaluate the conditions during/before BackendDAECreate?