Error Handling

Plugify handles errors differently in two places: while it loads and drives extensions, and while plugins call each other.

Errors the core handles

The core checks everything it does to an extension: reading the manifest, resolving dependencies, loading, exporting, starting, updating and stopping. A language module reports a failure by returning an error from the matching ILanguageModule method; an exception thrown from these methods is caught and treated the same way. The extension then gets the state Failed (or Corrupted, Unresolved, Disabled) with the reason, the extensions that depend on it are Skipped, and the rest keep working. After loading the core logs a report with the reason for every extension that did not start.

Calls between plugins

When a plugin calls a method of another plugin, the call goes straight to the native function of that method. The core is not in between, which is what keeps these calls fast, but it also means the core does not check them. What happens on an error depends on the language of the method that was called:

• Native code (C++, Go, Rust): a crash in the method is a crash of the process. A C++ exception must not leave an exported function.
• Languages with a runtime (C#, Python, JavaScript, Lua): the language module catches the error of the plugin code, logs it and returns a default value (zero, an empty string, and so on) to the caller. The caller does not learn that the call failed.

Recommendations for exported methods

{
  "name": "TryParse",
  "funcName": "TryParse",
  "paramTypes": [
    { "name": "text", "type": "string" },
    { "name": "value", "type": "int32", "ref": true }
  ],
  "retType": { "type": "bool" }
}

extern "C" bool TryParse(const plg::string& text, int32_t& value) {
    auto [ptr, ec] = std::from_chars(text.data(), text.data() + text.size(), value);
    return ec == std::errc{};
}