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//! Rust type -> Nim type mapping.
//!
//! Integer width is preserved exactly. Anything that cannot be represented
//! faithfully in Nim is reported as an error rather than approximated: a
//! silently widened integer would change the meaning of wrapping arithmetic,
//! which is precisely the kind of code people write in Rust.
use syn::{GenericArgument, PathArguments, Type, TypeParamBound};
#[derive(Debug, Clone, PartialEq)]
pub enum Nim {
Prim(String),
Seq(Box<Nim>),
OpenArray(Box<Nim>),
Array(usize, Box<Nim>),
Tuple(Vec<Nim>),
Named(String, Vec<Nim>),
Var(Box<Nim>),
/// `impl Fn(A) -> B` / `fn(A) -> B`. `nimcall` is the default calling
/// convention for a top-level proc, which is what Rust passes here.
Proc(Vec<Nim>, Box<Nim>),
Unit,
}
impl Nim {
pub fn render(&self) -> String {
match self {
Nim::Prim(s) => s.clone(),
Nim::Seq(t) => format!("seq[{}]", t.render()),
Nim::OpenArray(t) => format!("openArray[{}]", t.render()),
Nim::Array(n, t) => format!("array[{}, {}]", n, t.render()),
Nim::Tuple(ts) => {
let inner: Vec<String> = ts.iter().map(|t| t.render()).collect();
format!("({})", inner.join(", "))
}
Nim::Named(n, args) if args.is_empty() => n.clone(),
Nim::Named(n, args) => {
let inner: Vec<String> = args.iter().map(|t| t.render()).collect();
format!("{}[{}]", n, inner.join(", "))
}
Nim::Var(t) => format!("var {}", t.render()),
Nim::Proc(args, ret) => {
let inner: Vec<String> = args.iter().map(|t| t.render()).collect();
match &**ret {
Nim::Unit => format!("proc ({}) {{.nimcall.}}", inner.join(", ")),
r => format!("proc ({}): {} {{.nimcall.}}", inner.join(", "), r.render()),
}
}
Nim::Unit => "void".into(),
}
}
/// Owned form: a borrowed slice parameter is `openArray[T]`, but the same
/// type in an owned position (a field, a return value) must be `seq[T]`.
pub fn owned(self) -> Nim {
match self {
Nim::OpenArray(t) => Nim::Seq(t),
Nim::Var(t) => t.owned(),
other => other,
}
}
pub fn is_integer(&self) -> bool {
matches!(self, Nim::Prim(p) if matches!(p.as_str(),
"int8"|"int16"|"int32"|"int64"|"int"|
"uint8"|"uint16"|"uint32"|"uint64"|"uint"))
}
pub fn is_unsigned(&self) -> bool {
matches!(self, Nim::Prim(p) if p.starts_with("uint"))
}
}
pub fn prim(name: &str) -> Option<Nim> {
let mapped = match name {
"i8" => "int8",
"i16" => "int16",
"i32" => "int32",
"i64" => "int64",
"isize" => "int",
"u8" => "uint8",
"u16" => "uint16",
"u32" => "uint32",
"u64" => "uint64",
"usize" => "uint",
"f32" => "float32",
"f64" => "float64",
"bool" => "bool",
"char" => "Rune",
"str" | "String" => "string",
_ => return None,
};
Some(Nim::Prim(mapped.into()))
}
/// Types we refuse rather than approximate.
pub fn rejected(name: &str) -> Option<&'static str> {
match name {
"i128" | "u128" => Some("128-bit integers have no faithful Nim equivalent"),
_ => None,
}
}
fn ret_ty(r: &syn::ReturnType) -> Result<Nim, String> {
match r {
syn::ReturnType::Default => Ok(Nim::Unit),
syn::ReturnType::Type(_, t) => Ok(map(t)?.owned()),
}
}
pub fn map(t: &Type) -> Result<Nim, String> {
match t {
Type::Path(p) => {
let seg = p
.path
.segments
.last()
.ok_or_else(|| "empty type path".to_string())?;
let name = seg.ident.to_string();
if let Some(why) = rejected(&name) {
return Err(format!("unsupported type `{}`: {}", name, why));
}
let args: Vec<Nim> = match &seg.arguments {
PathArguments::AngleBracketed(a) => a
.args
.iter()
.filter_map(|g| match g {
GenericArgument::Type(t) => Some(map(t)),
_ => None,
})
.collect::<Result<_, _>>()?,
_ => vec![],
};
match (name.as_str(), args.len()) {
("Vec", 1) => Ok(Nim::Seq(Box::new(args[0].clone().owned()))),
("Option", 1) => Ok(Nim::Named("Option".into(), args)),
("Result", 2) => Ok(Nim::Named("Result".into(), args)),
("Box", 1) => Ok(args[0].clone()),
_ => {
if let Some(p) = prim(&name) {
Ok(p)
} else {
Ok(Nim::Named(name, args))
}
}
}
}
// &T is a value in Nim; &mut T becomes a `var` parameter. The caller
// decides whether a `var` is legal in the position it is used.
Type::Reference(r) => {
let inner = map(&r.elem)?;
if r.mutability.is_some() {
Ok(Nim::Var(Box::new(inner)))
} else {
Ok(inner)
}
}
Type::Slice(s) => Ok(Nim::OpenArray(Box::new(map(&s.elem)?))),
Type::Array(a) => {
let len = match &a.len {
syn::Expr::Lit(syn::ExprLit {
lit: syn::Lit::Int(i),
..
}) => i
.base10_parse::<usize>()
.map_err(|e| format!("array length: {}", e))?,
_ => return Err("array length must be a literal".into()),
};
Ok(Nim::Array(len, Box::new(map(&a.elem)?)))
}
Type::Tuple(t) if t.elems.is_empty() => Ok(Nim::Unit),
Type::Tuple(t) => Ok(Nim::Tuple(
t.elems.iter().map(map).collect::<Result<_, _>>()?,
)),
Type::Paren(p) => map(&p.elem),
Type::Group(g) => map(&g.elem),
Type::FnPtr(f) => {
let args: Vec<Nim> = f
.inputs
.iter()
.map(|a| map(&a.ty))
.collect::<Result<_, _>>()?;
Ok(Nim::Proc(args, Box::new(ret_ty(&f.output)?)))
}
Type::ImplTrait(i) => {
// `impl AsRef<[u8]>` and friends: fall back to the bound's own
// shape where we can recognise it, since Nim has no impl-trait.
for b in &i.bounds {
if let TypeParamBound::Trait(tb) = b {
if let Some(seg) = tb.path.segments.last() {
// `impl Fn(A) -> B` is a callable; Nim has a proc type
// for exactly this.
if seg.ident == "Fn" || seg.ident == "FnMut" || seg.ident == "FnOnce" {
if let PathArguments::Parenthesized(a) = &seg.arguments {
let args: Vec<Nim> = a
.inputs
.iter()
.map(|a| map(&a.ty))
.collect::<Result<_, _>>()?;
return Ok(Nim::Proc(args, Box::new(ret_ty(&a.output)?)));
}
}
if seg.ident == "AsRef" || seg.ident == "Into" {
if let PathArguments::AngleBracketed(a) = &seg.arguments {
for g in &a.args {
if let GenericArgument::Type(t) = g {
return map(t);
}
}
}
}
}
}
}
Err("unsupported `impl Trait` type".into())
}
Type::Infer(_) => Err("inferred type in a position that needs a name".into()),
other => Err(format!("unsupported type form: {:?}", discriminant(other))),
}
}
fn discriminant(t: &Type) -> &'static str {
match t {
Type::Ptr(_) => "raw pointer",
Type::TraitObject(_) => "trait object",
Type::Never(_) => "never",
Type::Macro(_) => "macro",
_ => "other",
}
}
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