add Optics proc macro

Cargo.toml

@@ -3,6 +3,8 @@ name = "bad-optics"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[workspace]
+members = ["bad-optics-derive"]
 
 [dependencies]
+bad-optics-derive = { path = "./bad-optics-derive" }

bad-optics-derive/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "bad-optics-derive"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = {version = "1.0", features = ["extra-traits"]}
+quote = "1.0"
+proc-macro2 = "1.0"

bad-optics-derive/src/lib.rs

@@ -0,0 +1,117 @@
+use std::collections::HashMap;
+
+use proc_macro2::{Span, TokenStream};
+use quote::quote;
+use syn::{parse_macro_input, DataStruct, DeriveInput, Field, Ident, Lit, Meta, Type, Visibility};
+
+// TODO add attributes to rename the lens/module/skip making lenses/idk
+
+#[proc_macro_derive(Optics, attributes(mod_name))]
+pub fn derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    // Parse the input tokens into a syntax tree
+    let input = parse_macro_input!(input as DeriveInput);
+
+    let name = &input.ident;
+    let mod_name = Ident::new(&get_mod_name(&input), Span::call_site());
+
+    let expanded = match input.data {
+        syn::Data::Struct(s) => expand_struct(s, name, &mod_name),
+        syn::Data::Enum(_) => todo!("not yet implemented for prisms"),
+        syn::Data::Union(_) => panic!("this macro does not work on unions"),
+    };
+
+    // Hand the output tokens back to the compiler
+    proc_macro::TokenStream::from(expanded)
+}
+
+fn get_mod_name(input: &DeriveInput) -> String {
+    for i in &input.attrs {
+        if let Ok(Meta::NameValue(meta)) = i.parse_meta() {
+            if let Some(ident) = meta.path.get_ident() {
+                if ident == "mod_name" {
+                    if let Lit::Str(a) = meta.lit {
+                        return a.value();
+                    }
+                }
+            }
+        }
+    }
+
+    input.ident.to_string().to_lowercase()
+}
+
+fn expand_struct(data: DataStruct, name: &Ident, mod_name: &Ident) -> TokenStream {
+    let fields = match &data.fields {
+        syn::Fields::Named(n) => n.named.iter(),
+        syn::Fields::Unnamed(_) => todo!(),
+        syn::Fields::Unit => todo!(),
+    }
+    .filter(|f| matches!(f.vis, Visibility::Public(_)));
+
+    let lens_funcs = fields
+        .clone()
+        .map(|field| {
+            let fname = field.ident.as_ref().unwrap();
+            let ty = &field.ty;
+            quote! {
+                pub fn #fname() ->
+                    bad_optics::lenses::Lens<bad_optics::lenses::lens::FuncLens<#name, #ty>>
+                {
+                    bad_optics::field_lens!(#name, #fname)
+                }
+            }
+        })
+        .collect::<TokenStream>();
+
+    let group_impls = group_by_type(fields)
+        .into_iter()
+        .map(|(ty, fields)| {
+            let lenses = fields
+                .into_iter()
+                .map(|field| {
+                    let fname = field.ident.unwrap();
+                    quote! {
+                        bad_optics::field_lens!(#name, #fname),
+                    }
+                })
+                .collect::<TokenStream>();
+
+            quote! {
+                impl Lenses<#ty> {
+                    pub fn get() ->
+                        Vec<bad_optics::lenses::Lens<bad_optics::lenses::lens::FuncLens<#name, #ty>>>
+                    {
+                        vec![
+                            #lenses
+                        ]
+                    }
+                }
+            }
+        })
+        .collect::<TokenStream>();
+
+    quote! {
+        pub mod #mod_name {
+            use super::*;
+
+            #lens_funcs
+
+            pub struct Lenses<T>(std::marker::PhantomData<T>);
+            #group_impls
+        }
+    }
+}
+
+fn group_by_type<'a>(fields: impl Iterator<Item = &'a Field>) -> Vec<(Type, Vec<Field>)> {
+    let mut map = HashMap::<Type, Vec<Field>>::new();
+
+    for field in fields {
+        if let Some(f) = map.get_mut(&field.ty) {
+            f.push(field.clone());
+        } else {
+            map.insert(field.ty.clone(), vec![field.clone()]);
+        }
+    }
+
+    map.into_iter().collect()
+}

examples/derive.rs

@@ -0,0 +1,46 @@
+use bad_optics::prelude::Optics;
+
+// the Optics derive macro will implement lenses for every public field in the struct
+// it makes a module named whatever the struct is called, but in lower case
+// you can rename the generated module by adding `#[mod_name = "other_name"]` to the struct
+
+#[derive(Optics, Clone, Debug)]
+pub struct MyStruct {
+    pub field1: String,
+    pub field2: String,
+
+    pub field3: u8,
+    _field4: u8,
+}
+
+fn main() {
+    let o = MyStruct {
+        field1: "first field".to_string(),
+        field2: "second field".to_string(),
+        field3: 12,
+        _field4: 1,
+    };
+
+    // we can manually get lenses for each field
+    // note that it's a function that returns a lens
+    let field1 = mystruct::field1();
+    let field2 = mystruct::field2();
+
+    // the lenses work normally as any other lens :)
+    assert_eq!(field1(o.clone()), "first field");
+    assert_eq!(field2(o.clone()), "second field");
+
+    // we can get a vec with all the lenses that match a type
+    let string_lenses = mystruct::Lenses::<String>::get();
+    assert_eq!(string_lenses.len(), 2);
+
+    // since _field4 is private, there's no lens for it
+    let vec_string_lenses = mystruct::Lenses::<u8>::get();
+    assert_eq!(vec_string_lenses.len(), 1);
+
+    let mut o = o;
+    for lens in string_lenses {
+        o = lens(o, |s| s.to_ascii_uppercase());
+    }
+    dbg!(o);
+}

src/lenses/fields.rs

@@ -1,7 +1,7 @@
 #[macro_export]
 macro_rules! field_lens {
     ($type:ident, $field:ident) => {
-        lens(
+        $crate::lenses::lens(
             |v: $type| v.$field,
             |mut u: $type, v| {
                 u.$field = v;

src/lib.rs

@@ -7,6 +7,8 @@ pub mod prisms;
 pub mod traversals;
 
 pub mod prelude {
+    pub use bad_optics_derive::Optics;
+
     pub use crate::combinations::*;
 
     pub use crate::lenses::*;