feat: introduce sizing methods to calculate needed bytes

Each struct and enum in a schema can now calculate its total encoded
byte size. As each collection must be iterated it can be a costly
operation but it might be faster (or sometimes even required) to
allocate a buffer upfront instead of dynamically growing it.

crates/stef-build/src/definition.rs

@@ -5,7 +5,7 @@ use stef_parser::{
     Module, NamedField, Schema, Struct, Type, TypeAlias, UnnamedField, Variant,
 };
 
-use super::{decode, encode};
+use super::{decode, encode, size};
 use crate::{BytesType, Opts};
 
 #[must_use]
@@ -14,7 +14,7 @@ pub fn compile_schema(opts: &Opts, Schema { definitions, .. }: &Schema<'_>) -> T
 
     quote! {
         #[allow(unused_imports)]
-        use ::stef::buf::{Decode, Encode};
+        use ::stef::buf::{Decode, Encode, Size};
 
         #(#definitions)*
     }
@@ -27,22 +27,26 @@ fn compile_definition(opts: &Opts, definition: &Definition<'_>) -> TokenStream {
             let def = compile_struct(opts, s);
             let encode = encode::compile_struct(opts, s);
             let decode = decode::compile_struct(opts, s);
+            let size = size::compile_struct(opts, s);
 
             quote! {
                 #def
                 #encode
                 #decode
+                #size
             }
         }
         Definition::Enum(e) => {
             let def = compile_enum(opts, e);
             let encode = encode::compile_enum(opts, e);
             let decode = decode::compile_enum(opts, e);
+            let size = size::compile_enum(opts, e);
 
             quote! {
                 #def
                 #encode
                 #decode
+                #size
             }
         }
         Definition::TypeAlias(a) => compile_alias(opts, a),
@@ -67,7 +71,7 @@ fn compile_module(
         #comment
         pub mod #name {
             #[allow(unused_imports)]
-            use ::stef::buf::{Decode, Encode};
+            use ::stef::buf::{Decode, Encode, Size};
 
             #(#definitions)*
         }

crates/stef-build/src/lib.rs

@@ -11,6 +11,7 @@ pub use self::definition::compile_schema;
 mod decode;
 mod definition;
 mod encode;
+mod size;
 
 pub type Result<T, E = Error> = std::result::Result<T, E>;