feat(convert): add derive macros for To and FromBytes

Cargo.toml

@@ -1,6 +1,6 @@
 [workspace]
 resolver = "2"
-members = ["extism-maturin", "manifest", "runtime", "libextism", "convert"]
+members = ["extism-maturin", "manifest", "runtime", "libextism", "convert", "convert-macros"]
 exclude = ["kernel"]
 
 [workspace.package]
@@ -14,4 +14,5 @@ version = "0.0.0+replaced-by-ci"
 [workspace.dependencies]
 extism = { path = "./runtime", version = "0.0.0+replaced-by-ci" }
 extism-convert = { path = "./convert", version = "0.0.0+replaced-by-ci" }
+extism-convert-macros = { path = "./convert-macros", version = "0.0.0+replaced-by-ci" }
 extism-manifest = { path = "./manifest", version = "0.0.0+replaced-by-ci" }

convert-macros/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "extism-convert-macros"
+readme = "./README.md"
+edition.workspace = true
+authors.workspace = true
+license.workspace = true
+homepage.workspace = true
+repository.workspace = true
+version.workspace = true
+description = "Macros to remove boilerplate with Extism"
+
+[lib]
+proc-macro = true
+
+[features]
+extism-path = []
+extism-pdk-path = []
+
+[dependencies]
+# manyhow = "0.10.4"
+manyhow.version = "0.11.0"
+proc-macro-crate = "3.1.0"
+proc-macro2 = "1.0.78"
+quote = "1.0.35"
+syn = { version = "2.0.48", features = ["derive"] }

convert-macros/src/lib.rs

@@ -0,0 +1,105 @@
+use std::iter;
+
+use manyhow::{ensure, manyhow, Result};
+use proc_macro_crate::{crate_name, FoundCrate};
+use quote::{format_ident, quote, ToTokens};
+use syn::{parse_quote, Attribute, DeriveInput, Path};
+
+/// Tries to resolve the path to `extism_convert` dynamically, falling back to feature flags when unsuccessful.
+fn convert_path() -> Path {
+    match crate_name("extism") {
+        Ok(FoundCrate::Name(name)) => {
+            let ident = format_ident!("{name}");
+            parse_quote!(::#ident::convert)
+        }
+        Ok(FoundCrate::Itself) => parse_quote!(crate::core),
+        Err(_) => match crate_name("extism-convert").or_else(|_| crate_name("extism_pdk")) {
+            Ok(FoundCrate::Name(name)) => {
+                let ident = format_ident!("{name}");
+                parse_quote!(::#ident)
+            }
+            Ok(FoundCrate::Itself) => parse_quote!(crate),
+            Err(_) => match () {
+                () if cfg!(feature = "extism-path") => parse_quote!(::extism::convert),
+                () if cfg!(feature = "extism-pdk-path") => parse_quote!(::extism_pdk),
+                _ => parse_quote!(::extism_convert),
+            },
+        },
+    }
+}
+
+fn extract_encoding(attrs: &[Attribute]) -> Result<Path> {
+    let encodings: Vec<_> = attrs
+        .iter()
+        .filter(|attr| attr.path().is_ident("encoding"))
+        .collect();
+    ensure!(!encodings.is_empty(), "encoding needs to be specified"; try = "`#[encoding(ToJson)]`");
+    ensure!(encodings.len() < 2, encodings[1], "only one encoding can be specified"; try = "remove `{}`", encodings[1].to_token_stream());
+
+    Ok(encodings[0].parse_args()?)
+}
+
+#[manyhow]
+#[proc_macro_derive(ToBytes, attributes(encoding))]
+pub fn to_bytes(
+    DeriveInput {
+        attrs,
+        ident,
+        generics,
+        ..
+    }: DeriveInput,
+) -> Result {
+    let encoding = extract_encoding(&attrs)?;
+    let convert = convert_path();
+
+    let (_, type_generics, _) = generics.split_for_impl();
+
+    let mut generics = generics.clone();
+    generics.make_where_clause().predicates.push(
+        parse_quote!(for<'__to_bytes_b> #encoding<&'__to_bytes_b Self>: #convert::ToBytes<'__to_bytes_b>)
+    );
+    generics.params = iter::once(parse_quote!('__to_bytes_a))
+        .chain(generics.params)
+        .collect();
+    let (impl_generics, _, where_clause) = generics.split_for_impl();
+
+    Ok(quote! {
+        impl #impl_generics #convert::ToBytes<'__to_bytes_a> for #ident #type_generics #where_clause
+        {
+            type Bytes = ::std::vec::Vec<u8>;
+
+            fn to_bytes(&self) -> Result<Self::Bytes, #convert::Error> {
+                #convert::ToBytes::to_bytes(&#encoding(self)).map(|__bytes| __bytes.as_ref().to_vec())
+            }
+        }
+
+    })
+}
+
+#[manyhow]
+#[proc_macro_derive(FromBytes, attributes(encoding))]
+pub fn from_bytes(
+    DeriveInput {
+        attrs,
+        ident,
+        mut generics,
+        ..
+    }: DeriveInput,
+) -> Result {
+    let encoding = extract_encoding(&attrs)?;
+    let convert = convert_path();
+    generics
+        .make_where_clause()
+        .predicates
+        .push(parse_quote!(#encoding<Self>: #convert::FromBytesOwned));
+    let (impl_generics, type_generics, where_clause) = generics.split_for_impl();
+    Ok(quote! {
+        impl #impl_generics #convert::FromBytesOwned for #ident #type_generics #where_clause
+        {
+            fn from_bytes_owned(__data: &[u8]) -> Result<Self, #convert::Error> {
+                <#encoding<Self> as #convert::FromBytesOwned>::from_bytes_owned(__data).map(|__encoding| __encoding.0)
+            }
+        }
+
+    })
+}

convert/Cargo.toml

@@ -18,6 +18,7 @@ protobuf = { version = "3.2.0", optional = true }
 rmp-serde = { version = "1.1.2", optional = true }
 serde = "1.0.186"
 serde_json = "1.0.105"
+extism-convert-macros.workspace = true
 
 [dev-dependencies]
 serde = { version = "1.0.186", features = ["derive"] }
@@ -26,3 +27,5 @@ serde = { version = "1.0.186", features = ["derive"] }
 default = ["msgpack", "prost", "raw"]
 msgpack = ["rmp-serde"]
 raw = ["bytemuck"]
+extism-path = ["extism-convert-macros/extism-path"]
+extism-pdk-path = ["extism-convert-macros/extism-pdk-path"]

convert/src/from_bytes.rs

@@ -1,5 +1,7 @@
 use crate::*;
 
+pub use extism_convert_macros::FromBytes;
+
 /// `FromBytes` is used to define how a type should be decoded when working with
 /// Extism memory. It is used for plugin output and host function input.
 pub trait FromBytes<'a>: Sized {

convert/src/to_bytes.rs

@@ -1,5 +1,7 @@
 use crate::*;
 
+pub use extism_convert_macros::ToBytes;
+
 /// `ToBytes` is used to define how a type should be encoded when working with
 /// Extism memory. It is used for plugin input and host function output.
 pub trait ToBytes<'a> {

runtime/Cargo.toml

@@ -22,7 +22,7 @@ url = "2"
 glob = "0.3"
 ureq = {version = "2.5", optional=true}
 extism-manifest = { workspace = true }
-extism-convert = { workspace = true }
+extism-convert = { workspace = true, features = ["extism-path"]}
 uuid = { version = "1", features = ["v4"] }
 libc = "0.2"