serde-rs
Support #[serde(default)] as a variant attribute for when the tag is not present
Yes, I know, that the relevant issue was closed, but because people ask for it again and again, and because the implementation is only in few lines, I made it.
Now you can place #[serde(default)] attribute on variant of internally tagged enum and if the tag is missing in map representation, then it would be assumed as default. Attribute does not change the seq representation of enum, because this create ambiguity when the first field of the content would be interpreted as a tag.
It seems that the #[serde(default)] attribute may also be supported for adjacently tagged enums, but that requires a bit more work and very likely to will conflict with #2935, so I left that for another PR.
Fixes #1410, fixes #1799, fixes #2231, closes #2476
