Add #[derive(ListBuild)]

derives/Cargo.toml

@@ -16,8 +16,9 @@ travis-ci = { repository = "lloydmeta/frunk" }
 proc-macro = true
 
 [dependencies]
-syn = "2"
+syn = { version = "2", features = ["full"] }
 quote = "1"
+proc-macro2 = "1.0.66"
 
 [dependencies.frunk_proc_macro_helpers]
 path = "../proc-macro-helpers"

derives/src/lib.rs

@@ -1,5 +1,6 @@
 #![recursion_limit = "128"]
 #![doc(html_playground_url = "https://play.rust-lang.org/")]
+#![cfg_attr(feature = "nightly", feature(proc_macro_diagnostic))]
 //! Frunk Derives
 //!
 //! This library holds logic for the nice custom derives in Frunk.
@@ -23,6 +24,8 @@ use crate::derive_generic::impl_generic;
 mod derive_labelled_generic;
 use crate::derive_labelled_generic::impl_labelled_generic;
 
+mod list_builder;
+
 use quote::ToTokens;
 
 /// Derives a Generic instance based on HList for
@@ -51,3 +54,41 @@ pub fn labelled_generic(input: TokenStream) -> TokenStream {
     // Return the generated impl
     gen.into_token_stream().into()
 }
+
+/// Constructs a struct using an `HList`.
+///
+/// This trait allows you to create an instance of a struct from an HList. You keep the
+/// remaining items in the `HList` after `DerivedListBuild::hl_new(...)`
+///
+/// # Examples
+///
+/// ```ignore
+/// use frunk::hlist::HList;
+/// use frunk::hlist;
+///
+/// #[derive(Debug, Eq, PartialEq, frunk::hlist::ListBuild)]
+/// struct ListConstructed {
+///     field0: bool,
+///     field1: u8,
+///     #[list_build_ignore]
+///     fn_built: &'static str,
+/// }
+///
+/// // Create a struct manually for comparison
+/// let manually_made = ListConstructed {
+///     field0: true,
+///     field1: 3,
+///     fn_built: "passed_in",
+/// };
+///
+/// // Use `hl_new` to construct a struct and remaining HList
+/// let (built, list): (ListConstructed, HList!(u32)) =
+///     ListConstructed::hl_new(hlist![true, 3u8, 42u32], "passed_in");
+///
+/// assert_eq!(built, manually_made);
+/// assert_eq!(list, hlist![42u32]);
+/// ```
+#[proc_macro_derive(ListBuild, attributes(list_build_ignore, plucker))]
+pub fn list_build(item: TokenStream) -> TokenStream {
+    list_builder::list_build_inner(item)
+}

derives/src/list_builder.rs

@@ -0,0 +1,168 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::quote;
+#[cfg(feature = "nightly")]
+use syn::spanned::Spanned;
+use syn::{
+    parse_macro_input, punctuated::Punctuated, token::Comma, Block, DeriveInput, GenericParam,
+    Generics, Stmt,
+};
+
+mod type_helpers;
+use type_helpers::{Annotation, ArgPair, PredicateVec, WhereLine};
+
+use self::type_helpers::AnnoErr;
+
+pub fn list_build_inner(item: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(item as DeriveInput);
+    // get the fields: the list-built fields, and the manually-built fields
+    let (input, list_built_fields, ignored_fields) = parse_fields(input);
+
+    let block = gen_stmts(&list_built_fields, &ignored_fields);
+
+    // hl_new args include the injected list, and values for the non-list built args
+    let args = ArgPair::make_args(ignored_fields);
+
+    if list_built_fields.len() == 0 {
+        panic!("redundant builder annotations");
+    }
+    let types = list_built_fields
+        .iter()
+        .map(|(ArgPair { tp, .. }, _)| tp.clone())
+        .collect::<Vec<_>>();
+
+    // make all where-clauses
+    let lines: Vec<WhereLine> = WhereLine::gen_lines_top(&types);
+
+    // Take the last clause and absorb that to make the ret-val
+    let ret = WhereLine::absorb(lines.last().expect("last line").clone());
+
+    let output = quote! { -> (Self, #ret) };
+    let where_clause: syn::WhereClause = PredicateVec::from(lines.clone()).into();
+    let gens = make_generic_params(list_built_fields.len());
+    let struct_ident = input.clone().ident;
+    let fun = quote! {
+        fn hl_new<#gens>(#(#args),*) #output
+        #where_clause
+        {
+            #block
+        }
+    };
+
+    // et, voile! en a des code magnifique!
+    quote! {
+        impl #struct_ident {
+            #fun
+        }
+    }
+    .into()
+}
+/// collects the field name/type pairs, splitting them according to fields being built by the list
+/// or as args passed into the constructor
+fn parse_fields(
+    mut input: DeriveInput,
+) -> (DeriveInput, Vec<(ArgPair, Option<syn::Expr>)>, Vec<ArgPair>) {
+    let mut list_built = Vec::new();
+    let mut ignored_fields = Vec::new();
+
+    if let syn::Data::Struct(syn::DataStruct {
+        fields: syn::Fields::Named(named),
+        ..
+    }) = &mut input.data
+    {
+        for field in &named.named {
+            // ignored and pluck-type are mutually exclusive...
+            match Annotation::try_from(&field.attrs[..]) {
+                Ok(Annotation::Plucker { ty, map }) => list_built.push((
+                    (field.ident.clone().expect("field_ident"), ty).into(),
+                    Some(map),
+                )),
+                Ok(Annotation::Ignore) => ignored_fields
+                    .push((field.ident.clone().expect("field_ident"), field.ty.clone()).into()),
+                Err(AnnoErr::NoMatch) => todo!(),
+                Err(AnnoErr::XOR) => {
+                    #[cfg(feature = "nightly")]
+                    field
+                        .span()
+                        .unwrap()
+                        .error("Redundant pluck-type on ignored field")
+                        .emit();
+                    #[cfg(not(feature = "nightly"))]
+                    panic!("don't ignore fields with pluckers");
+                }
+            };
+        }
+    }
+    (input, list_built, ignored_fields)
+}
+
+// `<L0, L1, ..., L(N-1)>` for the `fn hl_new<L1, ...>`
+fn make_generic_params(count: usize) -> Punctuated<GenericParam, Comma> {
+    let gens: String = (0..count + 1)
+        .map(|i| format!("L{}", i))
+        .collect::<Vec<String>>()
+        .join(", ");
+    let gens = format!("<{}>", gens);
+    syn::parse_str::<Generics>(&gens)
+        .expect("parsing the make_generic_params")
+        .params
+}
+
+// generates a line of code for each field that needs a value plucked out of the constructor list.
+// ```ignore
+// let (list_built0, l1) = frunk::hlist::Plucker::pluck(l0);
+// ```
+// ...and for the fileds ignored, just moves from the function argument to the rusulting structs
+// field
+fn gen_stmts(fields: &[(ArgPair, Option<syn::Expr>)], args: &[ArgPair]) -> Block {
+    let mut list_n = 0;
+    let mut stmts: Vec<Stmt> = vec![];
+    // Generate the "let (field, lX) = lY.pluck();" statements
+    for (arg_pair, expr) in fields {
+        let next_list = list_n + 1;
+        let next_list = syn::Ident::new(&format!("l{}", next_list), Span::call_site());
+        let list_n_tok = syn::Ident::new(&format!("l{}", list_n), Span::call_site());
+        let field_name = &arg_pair.ident;
+        let plucking = quote! {
+            let (#field_name, #next_list) = frunk::hlist::Plucker::pluck(#list_n_tok);
+        };
+
+        let stmt: Stmt = syn::parse2(plucking.clone())
+            .unwrap_or_else(|_| panic!("Failed to parse statement: {}", plucking.to_string()));
+
+        stmts.push(stmt);
+        if let Some(expr) = expr {
+            let mapping = quote! {
+                let #field_name = #expr;
+            };
+            stmts.push(syn::parse2(mapping).unwrap());
+        };
+        list_n += 1;
+    }
+
+    // Generate the "Self { fields... }" part of the block
+    let args = args
+        .iter()
+        .map(|ArgPair { ident, .. }| ident.clone())
+        .collect::<Vec<_>>();
+    let all_fields = [
+        &fields
+            .iter()
+            .map(|(field, _)| field.ident.clone())
+            .collect::<Vec<_>>()[..],
+        &args[..],
+    ]
+    .concat();
+    let list_n_ident = syn::Ident::new(&format!("l{}", list_n), proc_macro2::Span::call_site());
+    let self_stmt: Stmt = syn::parse2(quote! {
+        return (Self { #(#all_fields,)* }, #list_n_ident);
+    })
+    .expect("generating the Self...");
+    stmts.push(self_stmt);
+
+    Block {
+        stmts,
+        brace_token: Default::default(),
+    }
+}

derives/src/list_builder/type_helpers.rs

@@ -0,0 +1,8 @@
+mod arg_pair;
+pub(crate) use arg_pair::*;
+mod where_line;
+pub(crate) use where_line::*;
+mod pluck_param;
+pub(crate) use pluck_param::*;
+mod annotations;
+pub(crate) use annotations::*;

derives/src/list_builder/type_helpers/annotations.rs

@@ -0,0 +1,59 @@
+pub(crate) enum Annotation {
+    Plucker { ty: syn::Type, map: syn::Expr },
+    Ignore,
+}
+
+pub(crate) enum AnnoErr {
+    XOR,
+    NoMatch,
+}
+impl core::convert::TryFrom<&[syn::Attribute]> for Annotation {
+    type Error = AnnoErr;
+    fn try_from(attrs: &[syn::Attribute]) -> Result<Self, Self::Error> {
+        let mut annos = attrs.iter().filter_map(|attr| Self::try_from(attr).ok());
+        let Some(fst) = annos.next() else {
+            return Err(AnnoErr::NoMatch);
+        };
+
+        if let Some(_) = annos.next() {
+            return Err(AnnoErr::XOR);
+        }
+        Ok(fst)
+    }
+}
+impl TryFrom<&syn::Attribute> for Annotation {
+    type Error = ();
+
+    fn try_from(attr: &syn::Attribute) -> Result<Self, Self::Error> {
+        match attr.path().get_ident().map(|id| quote! {#id}.to_string()) {
+            Some(ref s) if s == "plucker" => {
+                let arg_parser = |input: syn::parse::ParseStream| {
+                    // Eg, with the arg: u8, map=core::convert::From::from(arg_name)
+
+                    // consume leading type
+                    let ty: syn::Type = input.parse().expect("type here");
+                    // , map=core::convert::From::from(arg_name)
+                    // consume comma
+                    let _ = input.parse::<Option<syn::Token![,]>>().expect("comma here");
+                    // map=core::convert::From::from(arg_name)
+                    // consume `map`
+                    let _ = input.parse::<syn::Ident>().expect("'map' here");
+                    // =core::convert::From::from(arg_name)
+                    // consume `=`
+                    input.parse::<syn::Token![=]>().expect("equalse sign here");
+                    // core::convert::From::from(arg_name)
+                    // parse in the expression
+                    let mapping = input.parse().expect("parsing expression");
+                    Ok((ty, mapping))
+                };
+
+                let (ty, map) = attr
+                    .parse_args_with(arg_parser)
+                    .expect("mapping with arg parser");
+                Ok(Annotation::Plucker { ty, map })
+            }
+            Some(ref s) if s == "list_build_ignore" => Ok(Self::Ignore),
+            _ => Err(()),
+        }
+    }
+}

derives/src/list_builder/type_helpers/arg_pair.rs

@@ -0,0 +1,46 @@
+// struct field or function argument
+pub(crate) struct ArgPair {
+    pub(crate) ident: syn::Ident,
+    pub(crate) tp: syn::Type,
+}
+
+impl ArgPair {
+    /// ```ignore
+    /// #[derive(ListBuild)]
+    /// struct Foo {
+    ///   foo: u8,
+    ///   #[list_build_ignore]
+    ///   bar: u16
+    /// }
+    /// // -> fn(l0: HList!(u8), bar: u16)
+    pub(crate) fn make_args(fields: Vec<ArgPair>) -> impl Iterator<Item = syn::FnArg> {
+        std::iter::once(syn::parse2(quote! {l0: L0}).unwrap())
+            .chain(fields.into_iter().map(syn::FnArg::from))
+    }
+}
+impl From<(syn::Ident, syn::Type)> for ArgPair {
+    fn from(value: (syn::Ident, syn::Type)) -> Self {
+        Self {
+            ident: value.0,
+            tp: value.1,
+        }
+    }
+}
+impl From<ArgPair> for syn::FnArg {
+    fn from(value: ArgPair) -> Self {
+        syn::FnArg::Typed(syn::PatType {
+            attrs: Vec::new(),
+            pat: Box::new(syn::Pat::Ident(syn::PatIdent {
+                attrs: Vec::new(),
+                by_ref: None,
+                mutability: None,
+                ident: value.ident.clone(),
+                subpat: None,
+            })),
+            colon_token: syn::token::Colon {
+                spans: [proc_macro2::Span::call_site()],
+            },
+            ty: Box::new(value.tp.clone()),
+        })
+    }
+}

derives/src/list_builder/type_helpers/pluck_param.rs

@@ -0,0 +1,12 @@
+use proc_macro2::Span;
+
+/// Shim to allow a type-conversions fom a type + LN pair into a paramater bound
+#[derive(Clone)]
+pub(crate) struct PluckParam(pub(crate) syn::TypeParamBound);
+impl From<(syn::Type, u8)> for PluckParam {
+    fn from((ty, n): (syn::Type, u8)) -> Self {
+        // Create an ident for "LN" where N is the u8 value
+        let l_ident = syn::Ident::new(&format!("L{}", n), Span::call_site());
+        return Self(syn::parse2(quote! {frunk::hlist::Plucker<#ty, #l_ident>}).unwrap());
+    }
+}