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use darling::{FromDeriveInput, FromField, FromVariant};
use proc_macro2::TokenStream;
use quote::{format_ident, quote, quote_spanned};
use syn::{parse_macro_input, spanned::Spanned, Data, DeriveInput};
#[derive(Default, FromMeta)]
struct DisplayFieldOpts {
/// Skip formatting this field or variant
#[darling(default)]
skip: bool,
/// Use this field when formatting extra data
#[darling(default)]
extra: bool,
}
#[derive(Default, FromMeta)]
struct DisplayVariantOpts {
/// Value to use as extra format instead of the variant name
#[darling(default)]
extra: Option<String>,
}
#[derive(FromField)]
#[darling(attributes(lang_util))]
struct NodeDisplayField {
ident: Option<syn::Ident>,
#[darling(default)]
display: DisplayFieldOpts,
}
#[derive(FromVariant)]
#[darling(attributes(lang_util))]
struct NodeDisplayVariant {
ident: syn::Ident,
fields: darling::ast::Fields<NodeDisplayField>,
#[darling(default)]
display: DisplayVariantOpts,
}
fn is_unit_enum(en: &syn::DataEnum) -> bool {
en.variants.iter().all(|variant| {
NodeDisplayVariant::from_variant(variant)
.map(|dv| dv.fields.style == darling::ast::Style::Unit)
.unwrap_or(false)
})
}
#[derive(Default, FromMeta)]
#[darling(default)]
struct NodeDisplay {
leaf: bool,
}
#[derive(FromDeriveInput)]
#[darling(attributes(lang_util))]
pub(crate) struct NodeDisplayOpts {
ident: syn::Ident,
generics: syn::Generics,
#[darling(default)]
display: NodeDisplay,
}
pub(crate) fn node_display(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
// Parse the input tokens into a syntax tree
let input = parse_macro_input!(input as DeriveInput);
// Find out struct-level options
let opts = NodeDisplayOpts::from_derive_input(&input).expect("failed to parse options");
// Add anonymous lifetimes as needed
let lifetimes: Vec<_> = opts.generics.lifetimes().map(|_| quote! { '_ }).collect();
// Generate the name of the target for usage in impl targets
let base_ident = &opts.ident;
let struct_name = if lifetimes.is_empty() {
quote! { #base_ident }
} else {
quote! { #base_ident<#(#lifetimes),*> }
};
// Is this a "Data" node?
let raw_name = base_ident
.to_string()
.strip_suffix("Data")
.map(|id| format_ident!("{}", id));
// The node name for the NodeDisplay impl
let node_name = raw_name.unwrap_or_else(|| base_ident.clone()).to_string();
let display_quoted = {
let display_extra_impl = {
let mut ts = TokenStream::new();
// TODO: Support `extra` on variant struct fields
match &input.data {
Data::Struct(st) => {
for (i, field) in st.fields.iter().enumerate() {
let df = NodeDisplayField::from_field(field)
.expect("failed to parse field attributes");
let ident = if let Some(id) = &df.ident {
quote! { #id }
} else {
let i = syn::Index::from(i);
quote! { #i }
};
if df.display.extra {
ts.extend(quote_spanned! {
field.span() =>
write!(f, " `{}`", self.#ident)?;
});
}
}
}
Data::Enum(en) => {
let mut match_body = TokenStream::new();
// Are the variants all units?
for variant in &en.variants {
let dv = NodeDisplayVariant::from_variant(variant)
.expect("failed to parse variant attributes");
let name = &dv.ident;
// Find out how to display the enum variant
let vs = dv
.display
.extra
.clone()
.unwrap_or_else(|| dv.ident.to_string());
// Fields pattern
let fields = match dv.fields.style {
darling::ast::Style::Unit => None,
darling::ast::Style::Tuple => {
let mut v = Vec::with_capacity(dv.fields.fields.len());
let ident = format_ident!("_");
for _ in 0..dv.fields.fields.len() {
v.push(ident.clone());
}
Some(quote! { (#(#v),*) })
}
darling::ast::Style::Struct => Some(quote! { { .. } }),
};
let quoted = quote_spanned! {
variant.span() =>
Self::#name #fields=> {
write!(f, " `{}`", #vs)?;
}
};
match_body.extend(quoted);
}
ts.extend(quote_spanned! {
input.span() => match self {
#match_body
};
});
}
Data::Union(_) => ts.extend(quote_spanned! {
input.span() =>
compile_error!("Unions are not supported");
}),
};
ts.extend(quote! { Ok(()) });
ts
};
let display_children_impl = if opts.display.leaf {
quote! { Ok(()) }
} else {
let mut ts = TokenStream::new();
ts.extend(quote! { use ::lang_util::node::NodeDisplay; });
match &input.data {
Data::Struct(st) => {
for (i, field) in st.fields.iter().enumerate() {
let df = NodeDisplayField::from_field(field)
.expect("failed to parse field attributes");
let ident = if let Some(id) = &df.ident {
quote! { #id }
} else {
let i = syn::Index::from(i);
quote! { #i }
};
ts.extend(quote_spanned! {
field.span() =>
write!(f, "{}", self.#ident.display().set_level(level))?;
});
}
}
Data::Enum(en) => {
let mut match_body = TokenStream::new();
if !is_unit_enum(en) {
for variant in &en.variants {
let dv = NodeDisplayVariant::from_variant(variant)
.expect("failed to parse variant attributes");
let name = &dv.ident;
if let darling::ast::Style::Unit = dv.fields.style {
let vs = dv.ident.to_string();
let quoted = quote_spanned! {
variant.span() =>
Self::#name => {
write!(f, "{}", ::lang_util::node::NodeDisplayWrapper::new(#vs, level))?;
}
};
match_body.extend(quoted);
} else if let darling::ast::Style::Tuple = dv.fields.style {
let mut variant_body = TokenStream::new();
let mut field_names = Vec::new();
for (i, field) in dv.fields.fields.iter().enumerate() {
// Add tuple identifier
let ff = if field.display.skip {
format_ident!("_")
} else {
format_ident!("tuple{}", i)
};
field_names.push(ff.clone());
// Add code
if !field.display.skip {
variant_body.extend(quote! {
write!(f, "{}", #ff.display().set_level(level))?;
});
}
}
match_body.extend(quote_spanned! {
variant.span() =>
Self::#name(#(#field_names),*) => {
#variant_body
}
});
} else {
let mut variant_body = TokenStream::new();
let mut field_names = Vec::new();
for field in &dv.fields.fields {
// Add tuple identifier
let ff = field.ident.as_ref().unwrap();
field_names.push(ff.clone());
// Add code
if !field.display.skip {
variant_body.extend(quote! {
write!(f, "{}", #ff.display().set_level(level))?;
});
}
}
match_body.extend(quote_spanned! {
variant.span() =>
Self::#name { #(#field_names),* } => {
#variant_body
}
});
}
}
ts.extend(quote_spanned! {
input.span() => match self {
#match_body
};
});
}
}
Data::Union(_) => ts.extend(quote_spanned! {
input.span() =>
compile_error!("Unions are not supported");
}),
};
ts.extend(quote! { Ok(()) });
ts
};
quote! {
#[automatically_derived]
impl ::lang_util::node::NodeContentDisplay for #struct_name {
fn name() -> Option<&'static str> {
Some(#node_name)
}
fn display_extra(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
#display_extra_impl
}
fn display_children(&self, level: usize, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
#display_children_impl
}
}
}
};
proc_macro::TokenStream::from(display_quoted)
}