Discuss about how to deprecate elements/conditions/features

[RiccardoRossi]

Description

we need to define an agile path to deprecating and eventually removing stuff.

@matekelemen can you post here your proposal?

[matekelemen]

I'm afraid there's no single mechanism we could use for everything we may want to deprecate. We have at least three categories:

1. C++ Classes registered in Registry/KratosComponents (elements, conditions, processes, etc.)
2. Other C++ classes and functions (e.g.: utilities, mappers, etc.)
3. Python-only classes (solvers, processes, orchestrators etc)

3 should be fairly simple. I wouldn't be surprised if python had a standard solution for it.

2 is the most difficult. If it's a utility, we can have a compile-time deprecation warning for it, but I can't stress enough that deprecation warnings are not enough: there has to be a deadline for removal. fyi

1 can be done relatively cleanly. How about storing an extra flag in KratosComponents with each entry that indicates whether they're deprecated (we can use Flags for this purpose if we want to store some extra tags later on)? Then we could issue a warning whenever someone asks for a deprecated entry.

class KratosComponents
...
-   using ComponentsContainerType = std::map<std::string, const TComponentType*>;
+   using ComponentsContainerType = std::map<std::string, std::pair<Flags,const TComponentType*>>;
...
    static ComponentsContainerType msComponents;
+   static std::pair<LockObject,std::unordered_set<std::string>> msUsedDeprecatedEntries;
...
static const TComponentType& Get(const std::string& rName)
    {
        auto it_comp =  msComponents.find(rName);
        KRATOS_DEBUG_ERROR_IF(it_comp == msComponents.end()) << GetMessageUnregisteredComponent(rName) << std::endl;
+       const auto& [r_flags, rp_entry] = it_comp->second;
+       if (r_flags.Is(DEPRECATED)) {
+           std::scoped_lock<LockObject> lock(msUsedDeprecatedEntries.first);
+           const bool first_use = msUsedDeprecatedEntries.second.emplace(it_comp->first).second;
+           KRATOS_WARN_IF(first_use) << it_comp->first << " is deprecated\n";
+       }
-       return *(it_comp->second);
+       return *(it_comp->second.second);
    }

[loumalouomega]

We used to have a macro to mark deprecated classes or functions. We can extend the macro so compilation fails if certain date is surpassed, forcing us to clean up the code.

[matekelemen]

C++ has a [[deprecated]] attribute. The question is how to insert a date, and how to do date comparison at compile time.

I also used to think that this would be a good idea, but now I'd be quite hesitant to do it. The main reason is reproducibility. What if I get a model using a specific version of Kratos, and I want to run it? I wouldn't be able to compile Kratos then.

If we ever want to venture into proper airspace applications, we'd have to be able to reproduce results from analyses done decades ago ...