Mavlink v2 extension are broken for v0.13 for the mavlink crate

[pv42]

The feature emit-extensions that is supposed to enable mavlink v2 extension does not currently work for versions 0.13.x. This can be seen when comaparing the documentation (which enables all features) of version 0.12.2 and 0.13.1 on docs.rs for COMMAND_ACK_DATA: https://docs.rs/mavlink/0.13.1/mavlink/common/struct.COMMAND_ACK_DATA.html only has the command and result fields while https://docs.rs/mavlink/0.12.2/mavlink/common/struct.COMMAND_ACK_DATA.html also contains the extension fields.

The reason for this is that the feature when enabled on the mavlink crate will not be set on the mavlink-bindgencrate which uses it when generating code. This can be fixed by adding the feature dependency in mavlink/Cargo.toml:

@@ -88,7 +88,7 @@ serde_arrays = { version = "0.1.0", optional = true }
 
 "format-generated-code" = []
 "emit-description" = []
-"emit-extensions" = []
+"emit-extensions" = ["mavlink-bindgen/emit-extensions"]
 "std" = ["mavlink-core/std"]
 "udp" = ["mavlink-core/udp"]
 "tcp" = ["mavlink-core/tcp"]

and adding the feature itself to mavlink-bindgen in mavlink-bindgen/Cargo.toml:

@@ -27,3 +27,4 @@ anstyle-parse = { version = "=0.2.1", optional=true }
 
 [features]
 cli = ["dep:clap", "dep:clap_lex", "dep:clap_builder", "dep:anstyle", "dep:anstyle-query", "dep:anstyle-parse"]
+emit-extensions=[]

There is a further issue when doing that, since the parser will use serde(default = "crate::RustDefault::rust_default")) and RustDefault is a pub (crate) is a trait in mavlink-core but required in the mavlink crate when using emit-extensions. The solution to this is making it fully public and importing it in mavlink/lib.rs. This does not create additional dependencies since mavlink already depends on mavlink-bindgen.

@@ -3,3 +3,6 @@
 include!(concat!(env!("OUT_DIR"), "/mod.rs"));
 
 pub use mavlink_core::*;
+
+#[cfg(feature = "emit-extensions")]
+#[allow(unused_imports)]
+pub (crate) use mavlink_core::utils::RustDefault;