# pyfunction.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-macros-backend-0.13.2/src/pyfunction.rs`.
Keywords: rust, rustlang, rust-lang

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    // Copyright (c) 2017-present PyO3 Project and Contributors

    use crate::module::add_fn_to_module;
    use proc_macro2::TokenStream;
    use syn::ext::IdentExt;
    use syn::parse::ParseBuffer;
    use syn::punctuated::Punctuated;
    use syn::spanned::Spanned;
    use syn::{NestedMeta, Path};

    #[derive(Debug, Clone, PartialEq)]
    pub enum Argument {
        VarArgsSeparator,
        VarArgs(syn::Path),
        KeywordArgs(syn::Path),
        Arg(syn::Path, Option<String>),
        Kwarg(syn::Path, Option<String>),
    }

    /// The attributes of the pyfunction macro
    #[derive(Default)]
    pub struct PyFunctionAttr {
        pub arguments: Vec<Argument>,
        has_kw: bool,
        has_varargs: bool,
        has_kwargs: bool,
        pub pass_module: bool,
    }

    impl syn::parse::Parse for PyFunctionAttr {
        fn parse(input: &ParseBuffer) -> syn::Result<Self> {
            let attr = Punctuated::<NestedMeta, syn::Token![,]>::parse_terminated(input)?;
            Self::from_meta(&attr)
        }
    }

    impl PyFunctionAttr {
        pub fn from_meta<'a>(iter: impl IntoIterator<Item = &'a NestedMeta>) -> syn::Result<Self> {
            let mut slf = PyFunctionAttr::default();

            for item in iter {
                slf.add_item(item)?
            }
            Ok(slf)
        }

        pub fn add_item(&mut self, item: &NestedMeta) -> syn::Result<()> {
            match item {
                NestedMeta::Meta(syn::Meta::Path(ident)) if ident.is_ident("pass_module") => {
                    self.pass_module = true;
                }
                NestedMeta::Meta(syn::Meta::Path(ident)) => self.add_work(item, ident)?,
                NestedMeta::Meta(syn::Meta::NameValue(nv)) => {
                    self.add_name_value(item, nv)?;
                }
                NestedMeta::Lit(lit) => {
                    self.add_literal(item, lit)?;
                }
                NestedMeta::Meta(syn::Meta::List(list)) => bail_spanned!(
                    list.span() => "list is not supported as argument"
                ),
            }
            Ok(())
        }

        fn add_literal(&mut self, item: &NestedMeta, lit: &syn::Lit) -> syn::Result<()> {
            match lit {
                syn::Lit::Str(lits) if lits.value() == "*" => {
                    // "*"
                    self.vararg_is_ok(item)?;
                    self.has_varargs = true;
                    self.arguments.push(Argument::VarArgsSeparator);
                    Ok(())
                }
                _ => bail_spanned!(item.span() => "expected \"*\""),
            }
        }

        fn add_work(&mut self, item: &NestedMeta, path: &Path) -> syn::Result<()> {
            ensure_spanned!(
                !(self.has_kw || self.has_kwargs),
                item.span() => "positional argument or varargs(*) not allowed after keyword arguments"
            );
            if self.has_varargs {
                self.arguments.push(Argument::Kwarg(path.clone(), None));
            } else {
                self.arguments.push(Argument::Arg(path.clone(), None));
            }
            Ok(())
        }

        fn vararg_is_ok(&self, item: &NestedMeta) -> syn::Result<()> {
            ensure_spanned!(
                !(self.has_kwargs || self.has_varargs),
                item.span() => "* is not allowed after varargs(*) or kwargs(**)"
            );
            Ok(())
        }

        fn kw_arg_is_ok(&self, item: &NestedMeta) -> syn::Result<()> {
            ensure_spanned!(
                !self.has_kwargs,
                item.span() => "keyword argument or kwargs(**) is not allowed after kwargs(**)"
            );
            Ok(())
        }

        fn add_nv_common(
            &mut self,
            item: &NestedMeta,
            name: &syn::Path,
            value: String,
        ) -> syn::Result<()> {
            self.kw_arg_is_ok(item)?;
            if self.has_varargs {
                // kw only
                self.arguments
                    .push(Argument::Kwarg(name.clone(), Some(value)));
            } else {
                self.has_kw = true;
                self.arguments
                    .push(Argument::Arg(name.clone(), Some(value)));
            }
            Ok(())
        }

        fn add_name_value(&mut self, item: &NestedMeta, nv: &syn::MetaNameValue) -> syn::Result<()> {
            match &nv.lit {
                syn::Lit::Str(litstr) => {
                    if litstr.value() == "*" {
                        // args="*"
                        self.vararg_is_ok(item)?;
                        self.has_varargs = true;
                        self.arguments.push(Argument::VarArgs(nv.path.clone()));
                    } else if litstr.value() == "**" {
                        // kwargs="**"
                        self.kw_arg_is_ok(item)?;
                        self.has_kwargs = true;
                        self.arguments.push(Argument::KeywordArgs(nv.path.clone()));
                    } else {
                        self.add_nv_common(item, &nv.path, litstr.value())?;
                    }
                }
                syn::Lit::Int(litint) => {
                    self.add_nv_common(item, &nv.path, format!("{}", litint))?;
                }
                syn::Lit::Bool(litb) => {
                    self.add_nv_common(item, &nv.path, format!("{}", litb.value))?;
                }
                _ => bail_spanned!(nv.lit.span() => "expected a string literal"),
            };
            Ok(())
        }
    }

    pub fn parse_name_attribute(attrs: &mut Vec<syn::Attribute>) -> syn::Result<Option<syn::Ident>> {
        let mut name_attrs = Vec::new();

        // Using retain will extract all name attributes from the attribute list
        attrs.retain(|attr| match attr.parse_meta() {
            Ok(syn::Meta::NameValue(nv)) if nv.path.is_ident("name") => {
                name_attrs.push((nv.lit, attr.span()));
                false
            }
            _ => true,
        });

        match name_attrs.as_slice() {
            [] => Ok(None),
            [(syn::Lit::Str(s), span)] => {
                let mut ident: syn::Ident = s.parse()?;
                // This span is the whole attribute span, which is nicer for reporting errors.
                ident.set_span(*span);
                Ok(Some(ident))
            }
            [(_, span)] => bail_spanned!(*span => "expected string literal for #[name] argument"),
            slice => bail_spanned!(
                slice[1].1 => "#[name] can not be specified multiple times"
            ),
        }
    }

    pub fn build_py_function(ast: &mut syn::ItemFn, args: PyFunctionAttr) -> syn::Result<TokenStream> {
        let python_name =
            parse_name_attribute(&mut ast.attrs)?.unwrap_or_else(|| ast.sig.ident.unraw());
        add_fn_to_module(ast, python_name, args)
    }

    #[cfg(test)]
    mod test {
        use super::{Argument, PyFunctionAttr};
        use proc_macro2::TokenStream;
        use quote::quote;
        use syn::parse_quote;

        fn items(input: TokenStream) -> syn::Result<Vec<Argument>> {
            let py_fn_attr: PyFunctionAttr = syn::parse2(input)?;
            Ok(py_fn_attr.arguments)
        }

        #[test]
        fn test_errs() {
            assert!(items(quote! {test="1", test2}).is_err());
            assert!(items(quote! {test, "*", args="*"}).is_err());
            assert!(items(quote! {test, kwargs="**", args="*"}).is_err());
            assert!(items(quote! {test, kwargs="**", args}).is_err());
        }

        #[test]
        fn test_simple_args() {
            let args = items(quote! {test1, test2, test3="None"}).unwrap();
            assert!(
                args == vec![
                    Argument::Arg(parse_quote! {test1}, None),
                    Argument::Arg(parse_quote! {test2}, None),
                    Argument::Arg(parse_quote! {test3}, Some("None".to_owned())),
                ]
            );
        }

        #[test]
        fn test_varargs() {
            let args = items(quote! {test1, test2="None", "*", test3="None"}).unwrap();
            assert!(
                args == vec![
                    Argument::Arg(parse_quote! {test1}, None),
                    Argument::Arg(parse_quote! {test2}, Some("None".to_owned())),
                    Argument::VarArgsSeparator,
                    Argument::Kwarg(parse_quote! {test3}, Some("None".to_owned())),
                ]
            );

            let args = items(quote! {"*", test1, test2}).unwrap();
            assert!(
                args == vec![
                    Argument::VarArgsSeparator,
                    Argument::Kwarg(parse_quote! {test1}, None),
                    Argument::Kwarg(parse_quote! {test2}, None),
                ]
            );

            let args = items(quote! {"*", test1, test2="None"}).unwrap();
            assert!(
                args == vec![
                    Argument::VarArgsSeparator,
                    Argument::Kwarg(parse_quote! {test1}, None),
                    Argument::Kwarg(parse_quote! {test2}, Some("None".to_owned())),
                ]
            );

            let args = items(quote! {"*", test1="None", test2}).unwrap();
            assert!(
                args == vec![
                    Argument::VarArgsSeparator,
                    Argument::Kwarg(parse_quote! {test1}, Some("None".to_owned())),
                    Argument::Kwarg(parse_quote! {test2}, None),
                ]
            );
        }

        #[test]
        fn test_all() {
            let args =
                items(quote! {test1, test2="None", args="*", test3="None", kwargs="**"}).unwrap();
            assert!(
                args == vec![
                    Argument::Arg(parse_quote! {test1}, None),
                    Argument::Arg(parse_quote! {test2}, Some("None".to_owned())),
                    Argument::VarArgs(parse_quote! {args}),
                    Argument::Kwarg(parse_quote! {test3}, Some("None".to_owned())),
                    Argument::KeywordArgs(parse_quote! {kwargs}),
                ]
            );
        }
    }