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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>),
/// `*mut T`. Nim's `ptr` is the same thing: an unmanaged address.
Ptr(Box<Nim>),
/// `*const T`. The const matters at the C level even though it does not at
/// the Rust one: Nim emits a real prototype where Rust emits none, and a
/// `char *` declaration against C's `const char *` is a compile error.
ConstPtr(Box<Nim>),
/// `impl Fn(A) -> B` / `fn(A) -> B`. Left at Nim's default calling
/// convention (`closure`), which accepts both a plain top-level proc and
/// a closure that captures -- and Rust's `impl Fn` accepts both too.
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::Ptr(t) => match &**t {
Nim::Prim(p) if p == "void" => "pointer".into(),
inner => format!("ptr {}", inner.render()),
},
Nim::ConstPtr(t) => match &**t {
Nim::Prim(p) if p == "void" => "pointer".into(),
inner => const_ptr_alias(inner),
},
Nim::Proc(args, ret) => {
// Nim's proc types name their parameters even when the name is
// never used.
let inner: Vec<String> = args
.iter()
.enumerate()
.map(|(i, t)| format!("a{}: {}", i, t.render()))
.collect();
match &**ret {
Nim::Unit => format!("proc ({})", inner.join(", ")),
r => format!("proc ({}): {}", inner.join(", "), r.render()),
}
}
Nim::Unit => "void".into(),
}
}
/// Strip a `var`, which is a parameter-passing mode rather than a type.
/// Unlike `owned`, this keeps a view a view.
pub fn unvar(self) -> Nim {
match self {
Nim::Var(t) => t.unvar(),
other => other,
}
}
/// 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"))
}
}
/// C types, as `libc` spells them. Nim has the same set under its own names,
/// and both are defined by the platform's C compiler, so these are equal by
/// construction rather than by assumption.
pub fn c_type(name: &str) -> Option<&'static str> {
Some(match name {
"c_char" => "cchar",
"c_schar" => "cschar",
"c_uchar" => "cuchar",
"c_short" => "cshort",
"c_ushort" => "cushort",
"c_int" => "cint",
"c_uint" => "cuint",
"c_long" => "clong",
"c_ulong" => "culong",
"c_longlong" => "clonglong",
"c_ulonglong" => "culonglong",
"c_float" => "cfloat",
"c_double" => "cdouble",
"size_t" => "csize_t",
"ssize_t" => "int",
"intptr_t" => "int",
"uintptr_t" => "uint",
"c_void" => "void",
_ => return None,
})
}
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",
other => match c_type(other) {
Some(c) => c,
None => 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,
}
}
/// The Nim type name for a const-qualified C pointer to `t`.
pub fn const_ptr_alias(t: &Nim) -> String {
format!("RsConstPtr{}", t.render().replace(' ', ""))
}
/// The C spelling of a Nim type, for a const-qualified pointer declaration.
pub fn c_spelling(t: &Nim) -> Option<&'static str> {
let Nim::Prim(p) = t else { return None };
Some(match p.as_str() {
"cchar" => "char",
"cschar" => "signed char",
"cuchar" => "unsigned char",
"cshort" => "short",
"cushort" => "unsigned short",
"cint" => "int",
"cuint" => "unsigned int",
"clong" => "long",
"culong" => "unsigned long",
"clonglong" => "long long",
"culonglong" => "unsigned long long",
"cfloat" => "float",
"cdouble" => "double",
"uint8" => "unsigned char",
"int8" => "signed char",
"uint16" => "unsigned short",
"int16" => "short",
"uint32" => "unsigned int",
"int32" => "int",
"uint64" => "unsigned long long",
"int64" => "long long",
_ => return 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()),
}
}
/// Types from `core::fmt` that must not be confused with a user type of the
/// same short name. `fmt::Error` and a crate's own `Error` are different
/// types, and collapsing a path to its last segment would merge them.
fn std_qualified(p: &syn::Path) -> Option<Nim> {
let segs: Vec<String> = p.segments.iter().map(|s| s.ident.to_string()).collect();
if segs.len() < 2 {
return None;
}
let (q, name) = (&segs[segs.len() - 2], segs.last()?.as_str());
if q != "fmt" {
return None;
}
Some(Nim::Prim(
match name {
"Error" => "FmtError",
"Formatter" => "Formatter",
// `fmt::Result` is `Result<(), fmt::Error>`. A formatting impl is
// lowered to a proc that returns the formatted string, so the
// result type is erased there; this spelling exists so that a
// signature mentioning it still maps to something.
"Result" => "FmtResult",
_ => return None,
}
.into(),
))
}
pub fn map(t: &Type) -> Result<Nim, String> {
match t {
Type::Path(p) => {
if let Some(n) = std_qualified(&p.path) {
return Ok(n);
}
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()) {
// The `log` facade's types, under shim names.
("Level", 0) => Ok(Nim::Prim("RsLogLevel".into())),
("LevelFilter", 0) => Ok(Nim::Prim("RsLogFilter".into())),
("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) => {
// `&str` is a borrowed view of characters, not an owned string.
// Nim accepts a `string` argument for an `openArray[char]`
// parameter, so a literal still passes straight through.
if let Type::Path(p) = &*r.elem {
if p.path.is_ident("str") {
return Ok(Nim::OpenArray(Box::new(Nim::Prim("char".into()))));
}
}
let inner = map(&r.elem)?;
if r.mutability.is_some() {
Ok(Nim::Var(Box::new(inner)))
} else {
Ok(inner)
}
}
Type::Ptr(p) => {
let inner = Box::new(map(&p.elem)?);
Ok(if matches!(p.mutability, syn::PointerMutability::Mut(_)) {
Nim::Ptr(inner)
} else {
Nim::ConstPtr(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)?)))
}
// `dyn Fn(A) -> B` is a callable, exactly as `impl Fn(A) -> B` is.
// Other trait objects need a vtable, which the lowering builds from
// the trait's declaration; `dyn` is spelled `<Trait>Dyn` there.
Type::TraitObject(t) => {
for b in &t.bounds {
if let TypeParamBound::Trait(tb) = b {
if let Some(seg) = tb.path.segments.last() {
let n = seg.ident.to_string();
if n == "Fn" || n == "FnMut" || n == "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)?)));
}
}
// `dyn T + Send + Sync`: the auto traits carry no
// methods, so the first real bound names the object.
if !matches!(n.as_str(), "Send" | "Sync" | "Unpin" | "Sized") {
return Ok(Nim::Named(format!("{n}Dyn"), vec![]));
}
}
}
}
Err("a trait object with no nameable trait bound".into())
}
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::TraitObject(_) => "trait object",
Type::Never(_) => "never",
Type::Macro(_) => "macro",
_ => "other",
}
}
|