bon_macros/builder/builder_gen/member/config/

mod.rs

// This lint occurs in code generated by `darling::FromAttributes`.
// TODO: report/fix this in `darling` upstream.
#![allow(clippy::needless_continue)]

mod blanket;
mod getter;
mod setters;
mod with;

pub(crate) use blanket::*;
pub(crate) use getter::*;
pub(crate) use setters::*;
pub(crate) use with::*;

use super::MemberOrigin;
use crate::builder::builder_gen::TopLevelConfig;
use crate::parsing::SpannedKey;
use crate::util::prelude::*;
use std::fmt;

#[derive(Debug, darling::FromAttributes)]
#[darling(attributes(builder))]
pub(crate) struct MemberConfig {
    /// Assign a default value to the member it it's not specified.
    ///
    /// An optional expression can be provided to set the value for the member,
    /// otherwise its [`Default`] trait impl will be used.
    #[darling(with = parse_optional_expr, map = Some)]
    pub(crate) default: Option<SpannedKey<Option<syn::Expr>>>,

    /// Make the member a private field in the builder struct.
    /// This is useful when the user needs to add custom fields to the builder,
    /// that they would use in the custom methods they add to the builder.
    ///
    /// This is similar to `skip`. The difference is that `field` is evaluated
    /// inside of the starting function, and stored in the builder. Its initialization
    /// expression thus has access to all `start_fn` parameters. It must be declared
    /// strictly after `#[builder(start_fn)]` members (if any) or right at the top of
    /// the members list.
    #[darling(with = parse_optional_expr, map = Some)]
    pub(crate) field: Option<SpannedKey<Option<syn::Expr>>>,

    /// Make the member gettable. [`GetterConfig`] specifies the signature for
    /// the getter.
    ///
    /// This takes the same attributes as the setter fns; `name`, `vis`, and `doc`
    /// and produces a getter method that returns the value of the member.
    /// By default, the value is returned by a shared reference (&T).
    pub(crate) getter: Option<SpannedKey<GetterConfig>>,

    /// Accept the value for the member in the finishing function parameters.
    pub(crate) finish_fn: darling::util::Flag,

    /// Enables an `Into` conversion for the setter method.
    pub(crate) into: darling::util::Flag,

    /// Rename the name exposed in the builder API.
    pub(crate) name: Option<syn::Ident>,

    /// Allows setting the value for the member repeatedly. This reduces the
    /// number of type states and thus increases the compilation performance.
    ///
    /// However, this also means that unintended overwrites won't be caught
    /// at compile time. Measure the compilation time before and after enabling
    /// this option to see if it's worth it.
    pub(crate) overwritable: darling::util::Flag,

    /// Disables the special handling for a member of type `Option<T>`. The
    /// member no longer has the default of `None`. It also becomes a required
    /// member unless a separate `#[builder(default = ...)]` attribute is
    /// also specified.
    pub(crate) required: darling::util::Flag,

    /// Configurations for the setter methods.
    #[darling(with = crate::parsing::parse_non_empty_paren_meta_list)]
    pub(crate) setters: Option<SettersConfig>,

    /// Skip generating a setter method for this member.
    ///
    /// An optional expression can be provided to set the value for the member,
    /// otherwise its  [`Default`] trait impl will be used.
    #[darling(with = parse_optional_expr, map = Some)]
    pub(crate) skip: Option<SpannedKey<Option<syn::Expr>>>,

    /// Accept the value for the member in the starting function parameters.
    pub(crate) start_fn: darling::util::Flag,

    /// Customize the setter signature and body with a custom closure or a well-known
    /// function. The closure/function must return the value of the type of the member,
    /// or optionally a `Result<_>` type where `_` is used to mark the type of
    /// the member. In this case the generated setters will be fallible
    /// (they'll propagate the `Result`).
    pub(crate) with: Option<SpannedKey<WithConfig>>,
}

#[derive(PartialEq, Eq, Clone, Copy)]
enum ParamName {
    Default,
    Field,
    Getter,
    FinishFn,
    Into,
    Name,
    Overwritable,
    Required,
    Setters,
    Skip,
    StartFn,
    With,
}

impl fmt::Display for ParamName {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let str = match self {
            Self::Default => "default",
            Self::Field => "field",
            Self::Getter => "getter",
            Self::FinishFn => "finish_fn",
            Self::Into => "into",
            Self::Name => "name",
            Self::Overwritable => "overwritable",
            Self::Required => "required",
            Self::Setters => "setters",
            Self::Skip => "skip",
            Self::StartFn => "start_fn",
            Self::With => "with",
        };
        f.write_str(str)
    }
}

impl MemberConfig {
    fn validate_mutually_exclusive(
        &self,
        attr_name: ParamName,
        attr_span: Span,
        mutually_exclusive: &[ParamName],
    ) -> Result<()> {
        self.validate_compat(attr_name, attr_span, mutually_exclusive, true)
    }

    fn validate_mutually_allowed(
        &self,
        attr_name: ParamName,
        attr_span: Span,
        mutually_allowed: &[ParamName],
    ) -> Result<()> {
        self.validate_compat(attr_name, attr_span, mutually_allowed, false)
    }

    fn validate_compat(
        &self,
        attr_name: ParamName,
        attr_span: Span,
        patterns: &[ParamName],
        mutually_exclusive: bool,
    ) -> Result<()> {
        let conflicting: Vec<_> = self
            .specified_param_names()
            .filter(|name| *name != attr_name && patterns.contains(name) == mutually_exclusive)
            .collect();

        if conflicting.is_empty() {
            return Ok(());
        }

        let conflicting = conflicting
            .iter()
            .map(|name| format!("`{name}`"))
            .join(", ");

        bail!(
            &attr_span,
            "`{attr_name}` attribute can't be specified together with {conflicting}",
        );
    }

    fn specified_param_names(&self) -> impl Iterator<Item = ParamName> {
        let Self {
            default,
            field,
            getter,
            finish_fn,
            into,
            name,
            overwritable,
            required,
            setters,
            skip,
            start_fn,
            with,
        } = self;

        let attrs = [
            (default.is_some(), ParamName::Default),
            (field.is_some(), ParamName::Field),
            (getter.is_some(), ParamName::Getter),
            (finish_fn.is_present(), ParamName::FinishFn),
            (into.is_present(), ParamName::Into),
            (name.is_some(), ParamName::Name),
            (overwritable.is_present(), ParamName::Overwritable),
            (required.is_present(), ParamName::Required),
            (setters.is_some(), ParamName::Setters),
            (skip.is_some(), ParamName::Skip),
            (start_fn.is_present(), ParamName::StartFn),
            (with.is_some(), ParamName::With),
        ];

        attrs
            .into_iter()
            .filter(|(is_present, _)| *is_present)
            .map(|(_, name)| name)
    }

    pub(crate) fn validate(&self, top_config: &TopLevelConfig, origin: MemberOrigin) -> Result {
        if top_config.const_.is_some() {
            self.require_const_compat()?;
        }

        if !cfg!(feature = "experimental-overwritable") && self.overwritable.is_present() {
            bail!(
                &self.overwritable.span(),
                "🔬 `overwritable` attribute is experimental and requires \
                 \"experimental-overwritable\" cargo feature to be enabled; \
                 we would be glad to make this attribute stable if you find it useful; \
                 please leave a 👍 reaction under the issue https://github.com/elastio/bon/issues/149 \
                 to help us measure the demand for this feature; it would be \
                 double-awesome if you could also describe your use case in \
                 a comment under the issue for us to understand how it's used \
                 in practice",
            );
        }

        if let Some(getter) = &self.getter {
            self.validate_mutually_exclusive(
                ParamName::Getter,
                getter.key.span(),
                &[ParamName::Overwritable],
            )?;
        }

        if self.start_fn.is_present() {
            self.validate_mutually_allowed(
                ParamName::StartFn,
                self.start_fn.span(),
                // TODO: add support for `#[builder(getter)]` with `start_fn`
                &[ParamName::Into],
            )?;
        }

        if self.finish_fn.is_present() {
            self.validate_mutually_allowed(
                ParamName::FinishFn,
                self.finish_fn.span(),
                &[ParamName::Into],
            )?;
        }

        if let Some(field) = &self.field {
            self.validate_mutually_allowed(ParamName::Field, field.key.span(), &[])?;
        }

        if let Some(skip) = &self.skip {
            match origin {
                MemberOrigin::FnArg => {
                    bail!(
                        &skip.key.span(),
                        "`skip` attribute is not supported on function arguments; \
                        use a local variable instead.",
                    );
                }
                MemberOrigin::StructField => {}
            }

            if let Some(Some(_expr)) = self.default.as_deref() {
                bail!(
                    &skip.key.span(),
                    "`skip` attribute can't be specified with the `default` attribute; \
                    if you wanted to specify a value for the member, then use \
                    the following syntax instead `#[builder(skip = value)]`",
                );
            }

            self.validate_mutually_allowed(ParamName::Skip, skip.key.span(), &[])?;
        }

        if let Some(with) = &self.with {
            self.validate_mutually_exclusive(ParamName::With, with.key.span(), &[ParamName::Into])?;
        }

        if let Some(setters) = &self.setters {
            if let Some(default) = &setters.doc.default {
                if self.default.is_none() {
                    bail!(
                        &default.key,
                        "`#[builder(setters(doc(default(...)))]` may only be specified \
                        when #[builder(default)] is also specified",
                    );
                }
            }
        }

        Ok(())
    }

    fn require_const_compat(&self) -> Result {
        fn validate_default_trait_or_expr(attr: &Option<SpannedKey<Option<syn::Expr>>>) -> Result {
            let attr = match attr {
                Some(attr) => attr,
                None => return Ok(()),
            };

            let name = attr.key.to_string();

            if let Some(expr) = &attr.value {
                return crate::parsing::require_embeddable_const_expr(expr);
            }

            bail!(
                &attr.key,
                "bare #[builder({name})] is incompatible with #[builder(const)] \
                because Default::default() can not be called in const context; \
                provide an explicit value via #[builder({name} = ...)] instead",
            )
        }

        validate_default_trait_or_expr(&self.default)?;
        validate_default_trait_or_expr(&self.skip)?;
        validate_default_trait_or_expr(&self.field)?;

        if self.into.is_present() {
            bail!(
                &self.into.span(),
                "#[builder(into)] is incompatible with #[builder(const)] \
                because Into::into() can not be called in const context",
            );
        }

        if let Some(getter) = &self.getter {
            if let Some(getter_kind) = &getter.kind {
                match &getter_kind.value {
                    GetterKind::Copy => {}
                    GetterKind::Clone => {
                        bail!(
                            &getter_kind.key,
                            "#[builder(getter(clone))] is incompatible with #[builder(const)] \
                            because Clone::clone() can not be called in const context",
                        )
                    }
                    GetterKind::Deref(_) => {
                        bail!(
                            &getter_kind.key,
                            "#[builder(getter(deref))] is incompatible with #[builder(const)] \
                            because Deref::deref() can not be called in const context",
                        )
                    }
                }
            }
        }

        if let Some(with) = &self.with {
            match &with.value {
                WithConfig::Closure(closure) => {
                    crate::parsing::require_embeddable_const_expr(&closure.body)?;
                }
                WithConfig::Some(_) => {}
                WithConfig::FromIter(from_iter) => {
                    bail!(
                        &from_iter,
                        "from_iter is incompatible with #[builder(const)] because \
                        FromIterator::from_iter() can not be called in const context",
                    )
                }
            }
        }

        Ok(())
    }
}

fn parse_optional_expr(meta: &syn::Meta) -> Result<SpannedKey<Option<syn::Expr>>> {
    match meta {
        syn::Meta::Path(path) => SpannedKey::new(path, None),
        syn::Meta::List(_) => Err(Error::unsupported_format("list").with_span(meta)),
        syn::Meta::NameValue(meta) => SpannedKey::new(&meta.path, Some(meta.value.clone())),
    }
}