add option to prevent derive(Default) for certain rust types

[stevelr]

I want to create an implementation of Default for my generated widl type that is not the standard rust Default implementation, but since src/generated.rs contains
#[derive(Debug, PartialEq, Deserialize, Serialize, Default, Clone)]
if I define my own impl Default for MyStruct in src/lib.rs, I get a compiler error that Default is already implemented.

My first thought was to suggest adding a cli flag to wapc generate such as --no-derive-default, to prevent Default from being generated, so I could create my own implementation in src/lib.rs.

But then I realized that if you have multiple struct types in the widl file, you might not want to implement Default for all of them, so a better implementation might be to add some lines to codegen.yml that give the name of the type and code-generation flags for that type, so if it's not overridden in codegen.yml, the Default would still be added to the generated derives list.

[autodidaddict]

Do you think something like this is applicable to other languages or just Rust? I think widl supports the ability to add annotations that may be used by language-specific generators...not sure if that's in main yet though @pkedy

[pkedy]

This would be a config setting for the Visitor class. I'm going to transfer this issue for tracking to wapc/widl-codegen-js (the new repo).

[stevelr]

This issue is no longer relevant for widl, and the feature is built into the smithy rust codegen.