bon_macros/builder/

item_impl.rs

use super::builder_gen::input_fn::{FnInputCtx, FnInputCtxParams, ImplCtx};
use super::builder_gen::TopLevelConfig;
use crate::normalization::{GenericsNamespace, SyntaxVariant};
use crate::parsing::BonCratePath;
use crate::util::prelude::*;
use darling::FromMeta;
use std::rc::Rc;
use syn::visit::Visit;
use syn::visit_mut::VisitMut;

#[derive(FromMeta)]
pub(crate) struct ImplInputParams {
    /// Overrides the path to the `bon` crate. This is useful when the macro is
    /// wrapped in another macro that also reexports `bon`.
    #[darling(rename = "crate", default)]
    bon: BonCratePath,
}

// ImplInputParams will evolve in the future where we'll probably want to move from it
#[allow(clippy::needless_pass_by_value)]
pub(crate) fn generate(
    impl_params: ImplInputParams,
    mut orig_impl_block: syn::ItemImpl,
) -> Result<TokenStream> {
    let mut namespace = GenericsNamespace::default();
    namespace.visit_item_impl(&orig_impl_block);

    if let Some((_, trait_path, _)) = &orig_impl_block.trait_ {
        bail!(trait_path, "Impls of traits are not supported yet");
    }

    let (builder_fns, other_items): (Vec<_>, Vec<_>) =
        orig_impl_block.items.into_iter().partition(|item| {
            let fn_item = match item {
                syn::ImplItem::Fn(fn_item) => fn_item,
                _ => return false,
            };

            fn_item
                .attrs
                .iter()
                .any(|attr| attr.path().is_ident("builder"))
        });

    if builder_fns.is_empty() {
        return Err(no_builder_attrs_error(&other_items));
    }

    orig_impl_block.items = builder_fns;

    // We do this back-and-forth with normalizing various syntax and saving original
    // to provide cleaner code generation that is easier to consume for IDEs and for
    // rust-analyzer specifically.
    //
    // For codegen logic we would like to have everything normalized. For example, we
    // want to assume `Self` is replaced with the original type and all lifetimes are
    // named, and `impl Traits` are desugared into type parameters.
    //
    // However, in output code we want to preserve existing `Self` references to make
    // sure rust-analyzer highlights them properly. If we just strip `Self` from output
    // code, then rust-analyzer won't be able to associate what `Self` token maps to in
    // the input. It would highlight `Self` as an "unresolved symbol"
    let mut norm_impl_block = orig_impl_block.clone();

    crate::normalization::NormalizeLifetimes::new(&namespace)
        .visit_item_impl_mut(&mut norm_impl_block);

    crate::normalization::NormalizeImplTraits::new(&namespace)
        .visit_item_impl_mut(&mut norm_impl_block);

    // Retain a variant of the impl block without the normalized `Self` mentions.
    // This way we preserve the original code that the user wrote with `Self` mentions
    // as much as possible, therefore IDE's are able to provide correct syntax highlighting
    // for `Self` mentions, because they aren't removed from the generated code output
    let mut norm_selfful_impl_block = norm_impl_block.clone();

    crate::normalization::NormalizeSelfTy {
        self_ty: &norm_impl_block.self_ty.clone(),
    }
    .visit_item_impl_mut(&mut norm_impl_block);

    let impl_ctx = Rc::new(ImplCtx {
        self_ty: norm_impl_block.self_ty,
        generics: norm_impl_block.generics,
        allow_attrs: norm_impl_block
            .attrs
            .iter()
            .filter_map(syn::Attribute::to_allow)
            .collect(),
    });

    let outputs = orig_impl_block
        .items
        .into_iter()
        .zip(norm_impl_block.items)
        .map(|(orig_item, norm_item)| {
            let norm_fn = match norm_item {
                syn::ImplItem::Fn(norm_fn) => norm_fn,
                _ => unreachable!(),
            };
            let orig_fn = match orig_item {
                syn::ImplItem::Fn(orig_fn) => orig_fn,
                _ => unreachable!(),
            };

            let norm_fn = conv_impl_item_fn_into_fn_item(norm_fn)?;
            let orig_fn = conv_impl_item_fn_into_fn_item(orig_fn)?;

            let mut config = TopLevelConfig::parse_for_fn(&orig_fn, None)?;

            if let BonCratePath::Explicit(path) = config.bon {
                bail!(
                    &path,
                    "`crate` parameter should be specified via `#[bon(crate = path::to::bon)]` \
                    when impl block syntax is used; no need to specify it in the method's \
                    `#[builder]` attribute"
                );
            }

            config.bon.clone_from(&impl_params.bon);

            let fn_item = SyntaxVariant {
                orig: orig_fn,
                norm: norm_fn,
            };

            let ctx = FnInputCtx::new(FnInputCtxParams {
                namespace: &namespace,
                fn_item,
                impl_ctx: Some(impl_ctx.clone()),
                config,
            })?;

            let adapted_fn = ctx.adapted_fn()?;
            let warnings = ctx.warnings();

            let mut output = ctx.into_builder_gen_ctx()?.output()?;
            output.other_items.extend(warnings);

            Result::<_>::Ok((adapted_fn, output))
        })
        .collect::<Result<Vec<_>>>()?;

    let new_impl_items = outputs.iter().flat_map(|(adapted_fn, output)| {
        let start_fn = &output.start_fn;
        [syn::parse_quote!(#adapted_fn), syn::parse_quote!(#start_fn)]
    });

    norm_selfful_impl_block.items = other_items;
    norm_selfful_impl_block.items.extend(new_impl_items);

    let other_items = outputs.iter().map(|(_, output)| &output.other_items);

    Ok(quote! {
        // Keep the original impl block at the top. It seems like rust-analyzer
        // does better job of highlighting syntax when it is here. Assuming
        // this is because rust-analyzer prefers the first occurrence of the
        // span when highlighting.
        //
        // See this issue for details: https://github.com/rust-lang/rust-analyzer/issues/18438
        #norm_selfful_impl_block

        #(#other_items)*
    })
}

fn conv_impl_item_fn_into_fn_item(func: syn::ImplItemFn) -> Result<syn::ItemFn> {
    let syn::ImplItemFn {
        attrs,
        vis,
        defaultness,
        sig,
        block,
    } = func;

    if let Some(defaultness) = &defaultness {
        bail!(defaultness, "Default functions are not supported yet");
    }

    Ok(syn::ItemFn {
        attrs,
        vis,
        sig,
        block: Box::new(block),
    })
}

fn no_builder_attrs_error(other_items: &[syn::ImplItem]) -> Error {
    let builder_like_err = other_items.iter().find_map(|item| {
        let item = match item {
            syn::ImplItem::Fn(fn_item) => fn_item,
            _ => return None,
        };

        let builder_like = item
            .attrs
            .iter()
            .find(|attr| attr.path().ends_with_segment("builder"))?;

        let builder_like_str = darling::util::path_to_string(builder_like.path());
        let builder_like_prefix = builder_like_str
            .strip_suffix("builder")
            .unwrap_or(&builder_like_str);

        Some(err!(
            &builder_like.path(),
            "#[bon] macro found no #[builder] attributes in the impl block, but \
            it looks like this attribute was meant for #[bon]; note that #[bon] \
            expects a bare #[builder] attribute without the `{builder_like_prefix}` \
            prefix; #[builder] acts as a simple config attribute for the active \
            #[bon] attribute in impl blocks; more info on inert vs active attributes: \
            https://doc.rust-lang.org/reference/attributes.html#active-and-inert-attributes"
        ))
    });

    if let Some(err) = builder_like_err {
        return err;
    }

    err!(
        &Span::call_site(),
        "there are no #[builder] functions in the impl block, so there is no \
        need for a #[bon] attribute here"
    )
}