wolfram-export-macros 0.6.0-alpha.6

//! Codegen for the three `#[export]` modes: native, `wstp`, and `wxf`.
//!
//! The emitted code names items under one of two host crates:
//! - `::wolfram_export::*`    — preferred (new canonical home, with feature flags)
//! - `::wolfram_library_link::*` — back-compat for older user crates
//!
//! [`resolve_host_crate`] inspects the *user's* `Cargo.toml` at expansion time
//! (via [`proc_macro_crate`]) and picks whichever crate they actually depend
//! on. This is how a single proc-macro crate can serve both the new and legacy
//! call sites without forcing users to choose at macro-name level.

use proc_macro::TokenStream;
use proc_macro2::{Delimiter, TokenStream as TokenStream2, TokenTree};

use proc_macro_crate::{crate_name, FoundCrate};
use quote::{format_ident, quote};
use syn::{spanned::Spanned, Error, Ident, Item, Meta, NestedMeta};

/// A parsed, not-yet-quoted `args = (...)`/`ret = ...` signature from
/// `#[export(margs, args = ..., ret = ...)]`. `args` has already been split
/// into one raw token-fragment per parameter (from inside the parens); `ret`
/// is the single raw fragment as-is. Each fragment is spliced verbatim into a
/// `wolfram_expr::expr!(..)` call at codegen time — see [`export_margs_function`].
pub(crate) struct MargsSignature {
    pub args: Vec<TokenStream2>,
    pub ret: TokenStream2,
}

/// Split a flat token stream on top-level commas. Bracketed/braced/parenthesized
/// groups (`[...]`, `(...)`, `{...}`) are already atomic `TokenTree::Group`s at
/// this level, so commas nested inside them are never mistaken for separators.
/// A trailing comma produces no extra empty segment.
fn split_top_level_commas(tokens: TokenStream2) -> Vec<TokenStream2> {
    let mut segments: Vec<TokenStream2> = vec![TokenStream2::new()];
    for tt in tokens {
        match &tt {
            TokenTree::Punct(p) if p.as_char() == ',' => {
                segments.push(TokenStream2::new())
            },
            _ => segments.last_mut().unwrap().extend(std::iter::once(tt)),
        }
    }
    if segments.last().is_some_and(TokenStream2::is_empty) {
        segments.pop();
    }
    segments
}

/// Pull the `args = ...`/`ret = ...` keyword arguments (if any) out of
/// `#[export(...)]`'s raw attribute token stream, returning the remaining
/// tokens (everything else, still comma-separated, ready for the existing
/// `syn::AttributeArgs`-based parser) plus each one's raw value tokens.
///
/// These two keys can't go through `syn::AttributeArgs`/`Meta` at all — that
/// grammar only accepts `key = <literal>`, and `args`/`ret` need arbitrary
/// `expr!`-style token trees (`::List[::Real, ::Real]`, `(::Real, ::Real)`,
/// …) as their value, which isn't a `syn::Lit`. So this runs as a raw
/// token-level pre-pass before any `syn` parsing happens.
pub(crate) fn extract_args_ret_tokens(
    attrs: TokenStream2,
) -> Result<(TokenStream2, Option<TokenStream2>, Option<TokenStream2>), Error> {
    let mut passthrough: Vec<TokenStream2> = Vec::new();
    let mut args_tokens: Option<TokenStream2> = None;
    let mut ret_tokens: Option<TokenStream2> = None;

    for segment in split_top_level_commas(attrs) {
        let mut iter = segment.clone().into_iter();
        let key_and_eq = match (iter.next(), iter.next()) {
            (Some(TokenTree::Ident(key)), Some(TokenTree::Punct(eq)))
                if eq.as_char() == '=' =>
            {
                Some(key)
            },
            _ => None,
        };
        let Some(key) = key_and_eq else {
            passthrough.push(segment);
            continue;
        };
        let key_name = key.to_string();
        if key_name != "args" && key_name != "ret" {
            passthrough.push(segment);
            continue;
        }

        let slot = if key_name == "args" {
            &mut args_tokens
        } else {
            &mut ret_tokens
        };
        if slot.is_some() {
            return Err(Error::new(
                key.span(),
                format!("duplicate `{key_name}` export attribute argument"),
            ));
        }
        let value: TokenStream2 = iter.collect();
        if value.is_empty() {
            return Err(Error::new(
                key.span(),
                format!("expected an expression after `{key_name} =`"),
            ));
        }
        *slot = Some(value);
    }

    let mut remaining = TokenStream2::new();
    for (i, segment) in passthrough.into_iter().enumerate() {
        if i > 0 {
            remaining.extend(std::iter::once(TokenTree::Punct(proc_macro2::Punct::new(
                ',',
                proc_macro2::Spacing::Alone,
            ))));
        }
        remaining.extend(segment);
    }

    Ok((remaining, args_tokens, ret_tokens))
}

/// Validate and shape the raw `args`/`ret` tokens extracted by
/// [`extract_args_ret_tokens`] into a [`MargsSignature`], enforcing that:
/// - they're only used with `Mode::Margs` (every other mode has its own
///   signature source: `FromArg`/`IntoArg` types, or a fixed wire shape);
/// - when given, both `args` and `ret` are given together;
/// - `args`'s value is a parenthesized, comma-separated list — `(t1, t2, ..)`
///   — one raw fragment per parameter (an empty `()` is a valid 0-arg spec).
pub(crate) fn parse_margs_signature(
    mode: Mode,
    args_tokens: Option<TokenStream2>,
    ret_tokens: Option<TokenStream2>,
) -> Result<Option<MargsSignature>, Error> {
    if mode != Mode::Margs {
        if let Some(bad) = args_tokens.or(ret_tokens) {
            return Err(Error::new_spanned(
                bad,
                "`args`/`ret` are only valid with `#[export(margs)]` — every \
                other mode gets its signature from Rust types (`FromArg`/`IntoArg`) \
                or has a fixed wire shape",
            ));
        }
        return Ok(None);
    }

    let (args_tokens, ret_tokens) = match (args_tokens, ret_tokens) {
        (Some(a), Some(r)) => (a, r),
        (None, None) => return Ok(None),
        (a, r) => {
            return Err(Error::new_spanned(
                a.or(r).unwrap(),
                "`#[export(margs, ...)]` requires both `args` and `ret` together, or neither",
            ));
        },
    };

    let mut iter = args_tokens.clone().into_iter();
    let group = match (iter.next(), iter.next()) {
        (Some(TokenTree::Group(g)), None) if g.delimiter() == Delimiter::Parenthesis => g,
        _ => {
            return Err(Error::new_spanned(
                args_tokens,
                "expected `args = (<type>, <type>, ..)` — a parenthesized, \
                comma-separated list of `expr!`-style argument type specs, one \
                per parameter",
            ));
        },
    };
    let args = split_top_level_commas(group.stream());

    Ok(Some(MargsSignature {
        args,
        ret: ret_tokens,
    }))
}

/// Which export shape (native MArgument / raw MArgument / WSTP Link / typed
/// WXF) the macro is generating.
#[derive(Copy, Clone, PartialEq, Eq)]
pub(crate) enum Mode {
    Native,
    Margs,
    Wstp,
    Wxf,
}

/// Path prefix the macro emits — points at the host crate that re-exports
/// the runtime helpers (`call_native_wolfram_library_function`, `ExportEntry`,
/// `inventory`, …). Determined dynamically at expansion time by inspecting
/// the user's `Cargo.toml` so both new users (on `wolfram-export`) and legacy
/// users (on `wolfram-library-link`) see correctly-resolving paths.
pub(crate) struct Prefix {
    pub crate_path: proc_macro2::TokenStream,
}

impl Prefix {
    /// Dynamic host-crate resolution. Prefers `wolfram-export` (the new
    /// canonical crate) and falls back to `wolfram-library-link` for back-
    /// compat. Returns a token stream usable as an absolute path prefix
    /// (`::wolfram_export`, `::wolfram_library_link`, or `crate` if the
    /// macro is called from inside one of those crates itself).
    pub fn resolve() -> Self {
        if let Some(tokens) = found_as("wolfram-export") {
            return Self { crate_path: tokens };
        }
        if let Some(tokens) = found_as("wolfram-library-link") {
            return Self { crate_path: tokens };
        }
        // Neither in the user's deps. Emit a path that will produce a clear
        // unresolved-import compile error at the use-site.
        Self {
            crate_path: quote! { ::__wolfram_export_or_wolfram_library_link_must_be_a_dependency },
        }
    }
}

/// Look up one crate name in the caller's `Cargo.toml`. Returns the path-prefix
/// token stream (`::<rename>`) if found, `None` otherwise.
///
/// We always emit an absolute external path, even when `proc-macro-crate`
/// returns `Itself` (meaning the caller's package owns this crate). Examples,
/// doctests, and integration tests within the same package all compile as
/// separate crates that import the library externally, so `crate::` would
/// resolve to the wrong root. The `#[export]` macro is only ever invoked from
/// those external-import contexts, never from within the library's own source.
fn found_as(name: &str) -> Option<TokenStream2> {
    let renamed = match crate_name(name).ok()? {
        FoundCrate::Itself => name.replace('-', "_"),
        FoundCrate::Name(n) => n,
    };
    let ident = format_ident!("{}", renamed);
    Some(quote! { ::#ident })
}

/// Identifier of the const-assert function the macro emits to surface a clear
/// compile error when the user picked the wrong feature on their host crate.
/// E.g. `Mode::Wxf` → `__assert_wxf_enabled`.
fn assert_fn_ident(mode: Mode) -> Ident {
    match mode {
        Mode::Native => format_ident!("__assert_native_enabled"),
        Mode::Margs => format_ident!("__assert_margs_enabled"),
        Mode::Wstp => format_ident!("__assert_wstp_enabled"),
        Mode::Wxf => format_ident!("__assert_wxf_enabled"),
    }
}

/// Detect the export mode from the keyword args: `margs`, `wstp`, `wxf`, or
/// native (default).
pub(crate) fn detect_mode_from_args(attrs: &syn::AttributeArgs) -> Mode {
    for attr in attrs {
        if let NestedMeta::Meta(Meta::Path(path)) = attr {
            if path.is_ident("margs") {
                return Mode::Margs;
            }
            if path.is_ident("wstp") {
                return Mode::Wstp;
            }
            if path.is_ident("wxf") {
                return Mode::Wxf;
            }
        }
    }
    Mode::Native
}

/// Drop the mode keyword (`margs`, `wstp`, `wxf`) from the arg list — only
/// meaningful to the dispatch shim; the regular arg parser would reject them.
pub(crate) fn strip_wstp_arg(attrs: syn::AttributeArgs) -> syn::AttributeArgs {
    attrs
        .into_iter()
        .filter(|attr| match attr {
            NestedMeta::Meta(Meta::Path(path)) => {
                !path.is_ident("margs") && !path.is_ident("wstp") && !path.is_ident("wxf")
            },
            _ => true,
        })
        .collect()
}

pub(crate) fn export(
    mode: Mode,
    attrs: syn::AttributeArgs,
    item: TokenStream,
    margs_signature: Option<MargsSignature>,
) -> Result<TokenStream2, Error> {
    let prefix = &Prefix::resolve();
    let ExportArgs {
        exported_name,
        hidden,
    } = parse_export_attribute_args(attrs)?;

    let item: Item = syn::parse(item)?;
    let func = match item {
        Item::Fn(func) => func,
        _ => {
            return Err(Error::new(
                proc_macro2::Span::call_site(),
                "this attribute can only be applied to `fn(..) {..}` items",
            ));
        },
    };

    if let Some(async_) = func.sig.asyncness {
        return Err(Error::new(
            async_.span(),
            "exported function cannot be `async`",
        ));
    }
    if let Some(lt) = func.sig.generics.lt_token {
        return Err(Error::new(lt.span(), "exported function cannot be generic"));
    }

    let name = func.sig.ident.clone();
    let exported_name: Ident = match exported_name {
        Some(name) => name,
        None => func.sig.ident.clone(),
    };
    let params = func.sig.inputs.clone();

    let wrapper = match mode {
        Mode::Native => {
            export_native_function(&name, &exported_name, params.len(), hidden, prefix)
        },
        Mode::Margs => {
            export_margs_function(&name, &exported_name, hidden, prefix, margs_signature)
        },
        Mode::Wstp => export_wstp_function(&name, &exported_name, params, hidden, prefix),
        Mode::Wxf => export_wxf_function(&name, &exported_name, params, hidden, prefix),
    };

    Ok(quote! {
        // Include the user's function in the output unchanged.
        #func

        #wrapper
    })
}

//--------------------------------------
// Native (MArgument) wrapper
//--------------------------------------

fn export_native_function(
    name: &Ident,
    exported_name: &Ident,
    parameter_count: usize,
    hidden: bool,
    prefix: &Prefix,
) -> TokenStream2 {
    let params = vec![quote! { _ }; parameter_count];
    let p = &prefix.crate_path;

    let assert_fn = assert_fn_ident(Mode::Native);
    let mut tokens = quote! {
        const _: () = #p::#assert_fn();

        mod #name {
            #[no_mangle]
            pub unsafe extern "C" fn #exported_name(
                lib: #p::sys::WolframLibraryData,
                argc: #p::sys::mint,
                args: *mut #p::sys::MArgument,
                res: #p::sys::MArgument,
            ) -> std::os::raw::c_int {
                let func: fn(#(#params),*) -> _ = super::#name;
                #p::macro_utils::call_native_wolfram_library_function(
                    lib,
                    args,
                    argc,
                    res,
                    func
                )
            }
        }
    };

    if !hidden && cfg!(feature = "automate-function-loading-boilerplate") {
        tokens.extend(quote! {
            #p::inventory::submit! {
                #p::macro_utils::LibraryLinkFunction::Native {
                    name: stringify!(#exported_name),
                    signature: || {
                        let func: fn(#(#params),*) -> _ = #name;
                        let func: &dyn #p::NativeFunction<'_> = &func;
                        func.signature()
                    }
                }
            }
        });
    }

    tokens
}

//--------------------------------------
// Margs (raw MArgument) wrapper
//--------------------------------------

/// Like [`export_native_function`], but the wrapped function always has the
/// fixed signature `fn(&[MArgument], MArgument)` — the user takes full manual
/// control over argument/return marshaling instead of going through
/// `FromArg`/`IntoArg`. Same C ABI as native mode, so it reuses
/// `call_native_wolfram_library_function`; only the signature handed to the
/// user's function differs.
fn export_margs_function(
    name: &Ident,
    exported_name: &Ident,
    hidden: bool,
    prefix: &Prefix,
    signature: Option<MargsSignature>,
) -> TokenStream2 {
    let p = &prefix.crate_path;

    // Emitted only when unannotated, and only inside this function's own
    // `mod #name { .. }` below — NOT at the shared outer scope, which is
    // common to every `#[export(margs)]` function in the file and would
    // collide on this constant's name across more than one of them.
    let missing_signature_warning = if signature.is_none() {
        quote! {
            #[deprecated(note = "\
                `#[export(margs)]` without `args`/`ret` defaults its LibraryFunctionLoad \
                signature to `LinkObject`/`LinkObject` (the same fixed placeholder \
                `#[export(wstp)]` uses) — add `args = (..)` and `ret = ..` to this \
                attribute to declare the real signature")]
            const __MARGS_SIGNATURE_MISSING: () = ();
            const _: () = __MARGS_SIGNATURE_MISSING;
        }
    } else {
        TokenStream2::new()
    };

    let assert_fn = assert_fn_ident(Mode::Margs);
    let mut tokens = quote! {
        const _: () = #p::#assert_fn();

        mod #name {
            #missing_signature_warning

            #[no_mangle]
            pub unsafe extern "C" fn #exported_name(
                lib: #p::sys::WolframLibraryData,
                argc: #p::sys::mint,
                args: *mut #p::sys::MArgument,
                res: #p::sys::MArgument,
            ) -> std::os::raw::c_int {
                // Underscores, not an explicit `&[MArgument]` annotation: a
                // written-out reference type elaborates to a higher-ranked
                // (`for<'r> fn(&'r [MArgument], _)`) fn pointer, which the
                // `NativeFunction<'a>` impl (generic over a *free* lifetime)
                // doesn't unify with. Inferring from `super::#name` instead
                // picks the same non-HRTB instantiation the plain native-mode
                // codegen below relies on.
                let func: fn(_, _) -> _ = super::#name;
                #p::macro_utils::call_native_wolfram_library_function(
                    lib,
                    args,
                    argc,
                    res,
                    func
                )
            }
        }
    };

    // `signature()` always returns a real `(Vec<Expr>, Expr)` — either built
    // from the user's `args = (..)`/`ret = ..` tokens (spliced verbatim into
    // `expr!` calls), or, when omitted, a default of the same fixed
    // `LinkObject`/`LinkObject` placeholder `#[export(wstp)]` uses (with a
    // compile-time nudge to add a real one, since a raw MArgument function
    // certainly doesn't actually take a WSTP `LinkObject`).
    //
    // `expr!` is referenced directly at its defining crate (`wolfram_expr`),
    // not through the `#p` host-crate indirection used elsewhere in this
    // file — a user annotating `args`/`ret` needs `wolfram-expr` as a direct
    // dependency regardless (it's the only place `Expr`/`expr!` come from).
    let signature_fn = match &signature {
        Some(MargsSignature { args, ret }) => quote! {
            || (
                ::std::vec![ #( ::wolfram_expr::expr!(#args) ),* ],
                ::wolfram_expr::expr!(#ret),
            )
        },
        None => quote! {
            || (
                ::std::vec![ ::wolfram_expr::expr!(::LinkObject) ],
                ::wolfram_expr::expr!(::LinkObject),
            )
        },
    };

    if !hidden && cfg!(feature = "automate-function-loading-boilerplate") {
        tokens.extend(quote! {
            #p::inventory::submit! {
                #p::macro_utils::LibraryLinkFunction::Margs {
                    name: stringify!(#exported_name),
                    signature: #signature_fn,
                }
            }
        });
    }

    tokens
}

//--------------------------------------
// WSTP (Link) wrapper
//--------------------------------------

fn export_wstp_function(
    name: &Ident,
    exported_name: &Ident,
    parameter_tys: syn::punctuated::Punctuated<syn::FnArg, syn::token::Comma>,
    hidden: bool,
    prefix: &Prefix,
) -> TokenStream2 {
    let p = &prefix.crate_path;
    let assert_fn = assert_fn_ident(Mode::Wstp);
    let mut tokens = quote! {
        const _: () = #p::#assert_fn();

        mod #name {
            use super::*;

            #[no_mangle]
            pub unsafe extern "C" fn #exported_name(
                lib: #p::sys::WolframLibraryData,
                raw_link: #p::wstp::sys::WSLINK,
            ) -> std::os::raw::c_int {
                let func: fn(#parameter_tys) -> _ = super::#name;
                #p::macro_utils::call_wstp_wolfram_library_function(
                    lib,
                    raw_link,
                    func
                )
            }
        }
    };

    if !hidden && cfg!(feature = "automate-function-loading-boilerplate") {
        tokens.extend(quote! {
            #p::inventory::submit! {
                #p::macro_utils::LibraryLinkFunction::Wstp {
                    name: stringify!(#exported_name)
                }
            }
        });
    }

    tokens
}

//--------------------------------------
// WXF (typed-arg ByteArray) wrapper
//--------------------------------------

fn export_wxf_function(
    name: &Ident,
    exported_name: &Ident,
    params: syn::punctuated::Punctuated<syn::FnArg, syn::token::Comma>,
    hidden: bool,
    prefix: &Prefix,
) -> TokenStream2 {
    let p = &prefix.crate_path;
    let n = params.len();
    let n_u64 = n as u64;

    // The user's parameter types, in declaration order. `self` (Receiver) is
    // not expected for free functions but we filter it out defensively.
    let param_types: Vec<&syn::Type> = params
        .iter()
        .filter_map(|arg| match arg {
            syn::FnArg::Typed(pt) => Some(&*pt.ty),
            _ => None,
        })
        .collect();

    let arg_idents: Vec<_> = (0..n).map(|i| quote::format_ident!("__arg{}", i)).collect();

    // Tuple-pattern with a trailing comma for the 1-arity case (Rust syntax).
    let tuple_pat = match arg_idents.len() {
        0 => quote! { () },
        1 => {
            let id = &arg_idents[0];
            quote! { (#id,) }
        },
        _ => quote! { (#(#arg_idents),*) },
    };
    // Tuple-expression of `<Ti as FromWXF>::from_wxf(__c)?` calls.
    let from_cursor_calls: Vec<_> = param_types
        .iter()
        .map(|t| {
            quote! { <#t as #p::macro_utils::FromWXF>::from_wxf(__c)? }
        })
        .collect();
    let tuple_read = match from_cursor_calls.len() {
        0 => quote! { () },
        1 => {
            let c = &from_cursor_calls[0];
            quote! { (#c,) }
        },
        _ => quote! { (#(#from_cursor_calls),*) },
    };

    let assert_fn = assert_fn_ident(Mode::Wxf);
    let mut tokens = quote! {
        const _: () = #p::#assert_fn();

        mod #name {
            use super::*;

            // Single ByteArray arg containing a WXF-serialized `List[args…]`.
            // The kernel retains ownership of the buffer (Constant mode), so
            // we take a reference. Panics (including deserialization failures
            // not caught explicitly) are converted to WXF-encoded Failure[]
            // expressions by `call_and_encode_panic`.
            fn __wxf_bridge(__input: &#p::macro_utils::NumericArray<u8>) -> #p::macro_utils::NumericArray<u8> {
                #p::macro_utils::call_and_encode_panic(|| {
                    // Read args, call the user fn, and serialize the result —
                    // ALL inside the closure, where the borrows into the input
                    // buffer are live. The closure returns an owned
                    // `NumericArray<u8>` (serialized in place, no intermediate
                    // Vec), which does not borrow the buffer, so zero-copy
                    // `&str` / `&[u8]` arguments are sound.
                    let __decoded = #p::macro_utils::decode_args(__input, #n_u64, |__c| {
                        let #tuple_pat = #tuple_read;
                        let __result = super::#name(#(#arg_idents),*);
                        #p::macro_utils::encode_result(&__result)
                    });
                    match __decoded {
                        ::core::result::Result::Ok(__bytes) => __bytes,
                        // Arg decoding failed: build a `Failure["ArgumentError", …]`
                        // from the `wolfram_serialize::Error` (it isn't a Failure itself).
                        ::core::result::Result::Err(__err) => {
                            #p::macro_utils::encode_arg_error(__err)
                        }
                    }
                })
            }

            #[no_mangle]
            pub unsafe extern "C" fn #exported_name(
                lib: #p::sys::WolframLibraryData,
                argc: #p::sys::mint,
                args: *mut #p::sys::MArgument,
                res: #p::sys::MArgument,
            ) -> std::os::raw::c_int {
                let func: fn(_) -> _ = __wxf_bridge;
                #p::macro_utils::call_wxf_wolfram_library_function(
                    lib,
                    args,
                    argc,
                    res,
                    func,
                )
            }
        }
    };

    if !hidden && cfg!(feature = "automate-function-loading-boilerplate") {
        tokens.extend(quote! {
            #p::inventory::submit! {
                #p::macro_utils::LibraryLinkFunction::Wxf {
                    name: stringify!(#exported_name),
                    signature: || #p::macro_utils::wxf_signature(),
                }
            }
        });
    }

    tokens
}

//======================================
// Parse `#[export(<attrs>)]` arguments
//======================================

/// Attribute arguments recognized by all three `#[export*]` macros (the `wstp`
/// mode keyword is no longer accepted — pick `#[export]` from the right
/// runtime crate instead).
struct ExportArgs {
    exported_name: Option<Ident>,
    hidden: bool,
}

fn parse_export_attribute_args(attrs: syn::AttributeArgs) -> Result<ExportArgs, Error> {
    let mut hidden = false;
    let mut exported_name: Option<Ident> = None;

    for attr in attrs {
        match attr {
            NestedMeta::Meta(ref meta) => match meta {
                Meta::Path(path) if path.is_ident("hidden") => {
                    if hidden {
                        return Err(Error::new(
                            attr.span(),
                            "duplicate export `hidden` attribute argument",
                        ));
                    }
                    hidden = true;
                },
                Meta::List(_) | Meta::Path(_) => {
                    return Err(Error::new(
                        attr.span(),
                        "unrecognized export attribute argument",
                    ));
                },
                Meta::NameValue(syn::MetaNameValue { path, lit, .. }) => {
                    if path.is_ident("name") {
                        if exported_name.is_some() {
                            return Err(Error::new(
                                attr.span(),
                                "duplicate definition for `name`",
                            ));
                        }
                        let lit_str = match lit {
                            syn::Lit::Str(str) => str,
                            _ => {
                                return Err(Error::new(
                                    lit.span(),
                                    "expected `name = \"...\"`",
                                ))
                            },
                        };
                        exported_name = Some(
                            lit_str
                                .parse::<Ident>()
                                .map_err(|err| Error::new(lit_str.span(), err))?,
                        );
                    } else {
                        return Err(Error::new(
                            path.span(),
                            "unrecognized export attribute named argument",
                        ));
                    }
                },
            },
            NestedMeta::Lit(_) => {
                return Err(Error::new(
                    attr.span(),
                    "unrecognized export attribute literal argument",
                ));
            },
        }
    }

    Ok(ExportArgs {
        exported_name,
        hidden,
    })
}