`sde compare` fails to detect output errors

[ToddFincannonEI]

The attached test model illustrates a case where the sde compare command fails to detect errors in C model output. It only occurs when a spec file gives output variables and subscripts are reordered.

1. Run validation-subs.mdl in Vensim and export to dat.
2. Run sde generate --genc --spec spec.json validation-subs
3. Run sde compile validation-subs
4. Run sde exec validation-subs
5. Run sde log --dat output/validation-subs.txt
6. Manually edit the output/validation-subs.txt file so that a[B1,A1] has a value of 0 at time 0.
7. Run sde compare validation-subs.dat output/validation-subs.dat. No errors are detected.

validation-subs.zip

[ToddFincannonEI]

The problem is that when a spec file gives output variables, they are converted from Vensim format to C format.

With a spec file, the emitIOCode function that creates headerVars gets output variables in C format. It then uses headerTitle in getHeader to convert them to Vensim format. The C format variables may have had their subscripts reordered into normal order. When converting to Vensim format, the subscripts remain in normal order. This does not match the Vensim dat file, where the subscripts are in the original model order. The sde compare function silently misses the variable. If the variable value is wrong in SDEverywhere, it goes undetected.

For instance, the test model contains the variable a[DimB, DimA] and the spec file contains output variable a[B1,A1]. The generated C file has a[a1,b1] in the output header.

We actually want the headerVars to be in Vensim format. This is the format used in the spec file, and is preserved as spec.outputVarNames. We don't actually need the C to Vensim format conversion. Simply use spec.outputVarNames, which makes the headerTitle function unnecessary.

If a spec file is not used, all variables are emitted to output. The headerVars are taken from the model in Vensim format, so none of this applies.

After applying the code-gen.js fix and running the above test sequence, the generated C file has a[B1,A1] in the output header. The subscript order matches Vensim, so sde compare detects the error.