This happens when wasmtime trap occurs during execution, for example when an unreachable statement is executed.

At least two of the libextism using sdks expect success when a zero is returned: cpp-sdk and perl-sdk

The python-sdk uses the presence of an error string also to determine if there's an error.

I can update the sdks to check for an error string instead, but I think it would be preferable to avoid the need to call extism_plugin_error every time you call a plugin function. The existing documentation for extism_plugin_call states Returns 0 when the call is successful.