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|
use proc_macro::TokenStream;
use quote::quote;
use syn::parse::{Parse, ParseStream};
use syn::{Expr, Ident, Token, braced};
// ── Parsing ─────────────────────────────────────────────────────────────────
/// Top-level item inside `tmpl! { }` or after the template ident in `tmpl!(tmpl, ...)`
enum TopItem {
/// `key = value` — simple parameter
Param { key: Ident, value: Expr },
/// `name { arm, arm, ... }` — implementation block
ImplBlock { name: Ident, arms: Vec<Arm> },
}
/// An arm inside an implementation block
enum Arm {
/// `key = value` — single-param arm
Single { key: Ident, value: Expr },
/// `{ key = value, key = value, ... }` — multi-param arm
Multi(Vec<(Ident, Expr)>),
}
// ── Parse implementations ──────────────────────────────────────────────────
impl Parse for TopItem {
fn parse(input: ParseStream) -> syn::Result<Self> {
let ident: Ident = input.parse()?;
let ahead = input.lookahead1();
if ahead.peek(Token![=]) {
let _eq: Token![=] = input.parse()?;
let value: Expr = input.parse()?;
Ok(TopItem::Param { key: ident, value })
} else if ahead.peek(syn::token::Brace) {
let content;
braced!(content in input);
let arms: Vec<Arm> = content
.parse_terminated(Arm::parse, Token![,])?
.into_iter()
.collect();
Ok(TopItem::ImplBlock { name: ident, arms })
} else {
Err(ahead.error())
}
}
}
impl Parse for Arm {
fn parse(input: ParseStream) -> syn::Result<Self> {
if input.peek(syn::token::Brace) {
let content;
braced!(content in input);
let params: Vec<(Ident, Expr)> = content
.parse_terminated(Self::parse_single, Token![,])?
.into_iter()
.collect();
Ok(Arm::Multi(params))
} else {
let (key, value) = Self::parse_single(input)?;
Ok(Arm::Single { key, value })
}
}
}
impl Arm {
fn parse_single(input: ParseStream) -> syn::Result<(Ident, Expr)> {
let key: Ident = input.parse()?;
let _eq: Token![=] = input.parse()?;
let value: Expr = input.parse()?;
Ok((key, value))
}
}
// ── Macro entry point ──────────────────────────────────────────────────────
fn split_input(input: ParseStream) -> syn::Result<(Ident, Vec<TopItem>)> {
// Try to parse: `ident , items` (explicit template variable)
// If the first token is an ident followed by `,`, it's explicit.
// Otherwise, default to `tmpl` and parse as items.
let first: Ident = input.parse()?;
if input.peek(Token![,]) {
let _comma: Token![,] = input.parse()?;
let items: Vec<TopItem> = input
.parse_terminated(TopItem::parse, Token![,])?
.into_iter()
.collect();
Ok((first, items))
} else {
// The first ident is actually the start of the first item.
// We need to re-parse. Use `syn::Result` to signal this.
// Tricky: we've already consumed `first`. Since syn::parse uses
// ParseStream which is a cursor, we actually can't rewind easily.
//
// Solution: use a custom approach — treat the first ident as
// the start of an item, and parse the rest as items.
let items = {
// Re-build: first ident + rest
let mut items: Vec<TopItem> = Vec::new();
// Parse the first item starting with `first`
let ahead = input.lookahead1();
if ahead.peek(Token![=]) {
let _eq: Token![=] = input.parse()?;
let value: Expr = input.parse()?;
items.push(TopItem::Param { key: first, value });
} else if ahead.peek(syn::token::Brace) {
let content;
braced!(content in input);
let arms: Vec<Arm> = content
.parse_terminated(Arm::parse, Token![,])?
.into_iter()
.collect();
items.push(TopItem::ImplBlock { name: first, arms });
} else {
return Err(ahead.error());
}
// Parse remaining items
while !input.is_empty() {
let _comma: Token![,] = input.parse()?;
if input.is_empty() {
break; // trailing comma
}
items.push(input.parse()?);
}
items
};
Ok((Ident::new("tmpl", proc_macro2::Span::call_site()), items))
}
}
#[proc_macro]
pub fn tmpl(input: TokenStream) -> TokenStream {
match syn::parse::Parser::parse(split_input, input) {
Ok((template_var, items)) => {
let stmts = generate(&template_var, &items);
let expanded = quote! { { #(#stmts)* } };
expanded.into()
}
Err(e) => e.to_compile_error().into(),
}
}
// ── Code generation ────────────────────────────────────────────────────────
fn generate(template_var: &Ident, items: &[TopItem]) -> Vec<proc_macro2::TokenStream> {
let mut stmts: Vec<proc_macro2::TokenStream> = Vec::new();
for item in items {
match item {
TopItem::Param { key, value } => {
let key_str = key.to_string();
stmts.push(quote! {
#template_var.insert_param(
#key_str.to_string(),
::std::string::ToString::to_string(&#value),
);
});
}
TopItem::ImplBlock { name, arms } => {
let name_str = name.to_string();
// Generate push statements for each arm
let push_stmts: Vec<proc_macro2::TokenStream> =
arms.iter().map(|arm| gen_arm_push(name, arm)).collect();
stmts.push(quote! {
let #name = #template_var.add_impl(#name_str.to_string());
#(#push_stmts)*
});
}
}
}
stmts
}
fn gen_arm_push(name: &Ident, arm: &Arm) -> proc_macro2::TokenStream {
match arm {
Arm::Single { key, value } => {
let key_str = key.to_string();
quote! {
#name.push(::std::collections::HashMap::from([
(#key_str.to_string(), ::std::string::ToString::to_string(&#value)),
]));
}
}
Arm::Multi(params) => {
let entries: Vec<_> = params
.iter()
.map(|(key, value)| {
let k = key.to_string();
quote! {
(#k.to_string(), ::std::string::ToString::to_string(&#value))
}
})
.collect();
quote! {
#name.push(::std::collections::HashMap::from([
#(#entries),*
]));
}
}
}
}
|
