implement #[derive(Params)] macro

coupler-derive/Cargo.toml

@@ -8,6 +8,6 @@ edition = "2021"
 proc-macro = true
 
 [dependencies]
-syn = "1.0"
+syn = { version = "2.0", features = ["full"] }
 quote = "1.0"
 proc-macro2 = "1.0"

coupler-derive/src/lib.rs

@@ -1,6 +1,228 @@
 use proc_macro::TokenStream;
+use quote::{quote, ToTokens};
+use syn::{parse_macro_input, Data, DeriveInput, Error, Expr, Fields, Ident, LitInt, LitStr, Type};
 
-#[proc_macro_derive(Params)]
-pub fn derive_params(_input: TokenStream) -> TokenStream {
-    TokenStream::new()
+struct ParamInfo {
+    ident: Ident,
+    ty: Type,
+    id: LitInt,
+    name: Option<LitStr>,
+    range: Option<Expr>,
+}
+
+fn parse_struct(input: &DeriveInput) -> Result<Vec<ParamInfo>, Error> {
+    let body = match &input.data {
+        Data::Struct(body) => body,
+        _ => {
+            return Err(Error::new_spanned(
+                &input,
+                "#[derive(Params)] can only be used on structs",
+            ));
+        }
+    };
+
+    let fields = match &body.fields {
+        Fields::Named(fields) => fields,
+        _ => {
+            return Err(Error::new_spanned(
+                &input,
+                "#[derive(Params)] can only be used on structs with named fields",
+            ));
+        }
+    };
+
+    let mut params = Vec::new();
+
+    for field in &fields.named {
+        let mut param_info = None;
+
+        for attr in &field.attrs {
+            if !attr.path().is_ident("param") {
+                continue;
+            }
+
+            if param_info.is_some() {
+                return Err(Error::new_spanned(&attr, "duplicate `param` attribute"));
+            }
+
+            let mut id = None;
+            let mut name = None;
+            let mut range = None;
+
+            attr.parse_nested_meta(|meta| {
+                let ident = meta.path.get_ident().ok_or_else(|| {
+                    Error::new_spanned(&meta.path, "expected this path to be an identifier")
+                })?;
+                if ident == "id" {
+                    if id.is_some() {
+                        return Err(Error::new_spanned(
+                            &meta.path,
+                            "duplicate param attribute `id`",
+                        ));
+                    }
+
+                    id = Some(meta.value()?.parse::<LitInt>()?);
+                } else if ident == "name" {
+                    if name.is_some() {
+                        return Err(Error::new_spanned(
+                            &meta.path,
+                            "duplicate param attribute `name`",
+                        ));
+                    }
+
+                    name = Some(meta.value()?.parse::<LitStr>()?);
+                } else if ident == "range" {
+                    if range.is_some() {
+                        return Err(Error::new_spanned(
+                            &meta.path,
+                            "duplicate param attribute `range`",
+                        ));
+                    }
+
+                    range = Some(meta.value()?.parse::<Expr>()?);
+                } else {
+                    return Err(Error::new_spanned(
+                        &meta.path,
+                        format!("unknown param attribute `{}`", ident),
+                    ));
+                }
+
+                Ok(())
+            })?;
+
+            let id = if let Some(id) = id {
+                id
+            } else {
+                return Err(Error::new_spanned(&attr, "missing `id` attribute"));
+            };
+
+            param_info = Some(ParamInfo {
+                ident: field.ident.clone().unwrap(),
+                ty: field.ty.clone(),
+                id,
+                name,
+                range,
+            });
+        }
+
+        if let Some(param_info) = param_info {
+            params.push(param_info);
+        }
+    }
+
+    Ok(params)
+}
+
+#[proc_macro_derive(Params, attributes(param))]
+pub fn derive_params(input: TokenStream) -> TokenStream {
+    let input: DeriveInput = parse_macro_input!(input as DeriveInput);
+
+    let params = match parse_struct(&input) {
+        Ok(params) => params,
+        Err(err) => {
+            return err.into_compile_error().into();
+        }
+    };
+
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+    let ident = &input.ident;
+
+    let ranges: Vec<_> = params
+        .iter()
+        .map(|param| {
+            if let Some(range) = &param.range {
+                range.to_token_stream()
+            } else {
+                let ty = &param.ty;
+                quote! { <#ty as ::coupler::param::DefaultRange>::default_range() }
+            }
+        })
+        .collect();
+
+    let params_expanded = params.iter().zip(&ranges).map(|(param, range)| {
+        let ident = &param.ident;
+        let ty = &param.ty;
+        let id = &param.id;
+
+        let name = if let Some(name) = &param.name {
+            name.clone()
+        } else {
+            LitStr::new(&param.ident.to_string(), param.ident.span())
+        };
+
+        quote! {
+            ::coupler::param::ParamInfo {
+                id: #id,
+                name: ::std::string::ToString::to_string(#name),
+                default: ::coupler::param::Range::<#ty>::encode(&(#range), __default.#ident),
+                steps: ::coupler::param::Range::<#ty>::steps(&(#range)),
+                parse: ::std::boxed::Box::new(|__str| {
+                    match <#ty as ::std::str::FromStr>::from_str(__str) {
+                        ::std::result::Result::Ok(__value) => {
+                            Some(::coupler::param::Range::<#ty>::encode(&(#range), __value))
+                        }
+                        ::std::result::Result::Err(_) => None,
+                    }
+                }),
+                display: ::std::boxed::Box::new(|__value, __formatter| {
+                    ::std::fmt::Display::fmt(
+                        &::coupler::param::Range::<#ty>::decode(&(#range), __value),
+                        __formatter
+                    )
+                }),
+            }
+        }
+    });
+
+    let set_cases = params.iter().zip(&ranges).map(|(param, range)| {
+        let ident = &param.ident;
+        let ty = &param.ty;
+        let id = &param.id;
+
+        quote! {
+            #id => {
+                self.#ident = ::coupler::param::Range::<#ty>::decode(&(#range), __value);
+            }
+        }
+    });
+
+    let get_cases = params.iter().zip(&ranges).map(|(param, range)| {
+        let ident = &param.ident;
+        let ty = &param.ty;
+        let id = &param.id;
+
+        quote! {
+            #id => {
+                ::coupler::param::Range::<#ty>::encode(&(#range), self.#ident)
+            }
+        }
+    });
+
+    let expanded = quote! {
+        impl #impl_generics ::coupler::param::Params for #ident #ty_generics #where_clause {
+            fn params() -> ::std::vec::Vec<::coupler::param::ParamInfo> {
+                let __default: #ident #ty_generics = ::std::default::Default::default();
+
+                ::std::vec![
+                    #(#params_expanded,)*
+                ]
+            }
+
+            fn set_param(&mut self, __id: ::coupler::ParamId, __value: ::coupler::ParamValue) {
+                match __id {
+                    #(#set_cases)*
+                    _ => {}
+                }
+            }
+
+            fn get_param(&self, __id: ::coupler::ParamId) -> ::coupler::ParamValue {
+                match __id {
+                    #(#get_cases)*
+                    _ => 0.0,
+                }
+            }
+        }
+    };
+
+    expanded.into()
 }

examples/gain/Cargo.toml

@@ -9,4 +9,4 @@ publish = false
 formats = ["clap", "vst3"]
 
 [dependencies]
-coupler = { workspace = true }
+coupler = { workspace = true, features = ["derive"] }

examples/gain/src/lib.rs

@@ -4,10 +4,20 @@ use coupler::format::clap::*;
 use coupler::format::vst3::*;
 use coupler::{buffers::*, bus::*, events::*, param::*, parent::*, *};
 
-const GAIN: ParamId = 0;
+#[derive(Params, Clone)]
+struct GainParams {
+    #[param(id = 0, name = "Gain", range = 0.0..1.0)]
+    gain: f32,
+}
+
+impl Default for GainParams {
+    fn default() -> GainParams {
+        GainParams { gain: 1.0 }
+    }
+}
 
 pub struct Gain {
-    gain: f64,
+    params: GainParams,
 }
 
 impl Plugin for Gain {
@@ -33,52 +43,41 @@ impl Plugin for Gain {
                     formats: vec![Format::Mono],
                 },
             ],
-            params: vec![ParamInfo {
-                id: GAIN,
-                name: "Gain".to_string(),
-                default: 1.0,
-                steps: None,
-                parse: Box::new(|s| s.parse().ok()),
-                display: Box::new(|v, f| write!(f, "{:.2}", v)),
-            }],
+            params: GainParams::params(),
         }
     }
 
     fn new(_host: Host) -> Self {
-        Gain { gain: 1.0 }
+        Gain {
+            params: GainParams::default(),
+        }
     }
 
     fn set_param(&mut self, id: ParamId, value: ParamValue) {
-        match id {
-            GAIN => self.gain = value,
-            _ => {}
-        }
+        self.params.set_param(id, value);
     }
 
     fn get_param(&self, id: ParamId) -> ParamValue {
-        match id {
-            GAIN => self.gain,
-            _ => 0.0,
-        }
+        self.params.get_param(id)
     }
 
     fn save(&self, output: &mut impl Write) -> io::Result<()> {
-        output.write(&self.gain.to_le_bytes())?;
+        output.write(&self.params.gain.to_le_bytes())?;
 
         Ok(())
     }
 
     fn load(&mut self, input: &mut impl Read) -> io::Result<()> {
-        let mut buf = [0; std::mem::size_of::<f64>()];
+        let mut buf = [0; std::mem::size_of::<f32>()];
         input.read_exact(&mut buf)?;
-        self.gain = f64::from_le_bytes(buf);
+        self.params.gain = f32::from_le_bytes(buf);
 
         Ok(())
     }
 
     fn processor(&self, _config: Config) -> Self::Processor {
         GainProcessor {
-            gain: self.gain as f32,
+            params: self.params.clone(),
         }
     }
 
@@ -104,15 +103,12 @@ impl ClapPlugin for Gain {
 }
 
 pub struct GainProcessor {
-    gain: f32,
+    params: GainParams,
 }
 
 impl Processor for GainProcessor {
     fn set_param(&mut self, id: ParamId, value: ParamValue) {
-        match id {
-            GAIN => self.gain = value as f32,
-            _ => {}
-        }
+        self.params.set_param(id, value);
     }
 
     fn reset(&mut self) {}
@@ -121,7 +117,7 @@ impl Processor for GainProcessor {
         for event in events {
             match event.data {
                 Data::ParamChange { id, value } => {
-                    self.set_param(id, value);
+                    self.params.set_param(id, value);
                 }
                 _ => {}
             }
@@ -133,7 +129,7 @@ impl Processor for GainProcessor {
 
         for i in 0..main.channel_count() {
             for sample in &mut main[i] {
-                *sample *= self.gain;
+                *sample *= self.params.gain;
             }
         }
     }