globetrotter-rust 0.0.13

//! Rust bindings code generation for globetrotter translations.

/// Rust code generation configuration types.
pub mod config;

pub use config::OutputConfig;

use convert_case::{Case, Casing};
use globetrotter_model as model;
use quote::{format_ident, quote};

/// Common header inserted at the top of generated Rust files.
#[must_use]
pub fn preamble() -> String {
    indoc::formatdoc!(
        r"
            //
            // AUTOGENERATED. DO NOT EDIT.
            // generated by globetrotter v{version}.
            //
        ",
        version = std::env!("CARGO_PKG_VERSION"),
    )
}

fn argument_to_rust_field_name(name: &str) -> String {
    let field_name = name.replace(' ', "").replace(['-', '.'], "_");
    field_name.to_case(Case::Snake)
}

/// The Rust enum variant identifier generated for a translation key, e.g.
/// `translation.greeting` becomes `TranslationGreeting`.
#[must_use]
pub fn key_to_rust_enum_variant(key: &str) -> String {
    let variant_name = key.replace(' ', "").replace(['-', '.'], "_");
    variant_name.to_case(Case::UpperCamel)
}

/// The comparison traits a generated field type implements.
///
/// The generated enum can only derive a comparison trait when every field
/// implements it, so these are combined across fields with [`Self::and`].
#[derive(Clone, Copy, Debug)]
struct Comparisons {
    eq: bool,
    partial_ord: bool,
    ord: bool,
}

impl Comparisons {
    /// `Eq` and `Ord`, as implemented by integers, booleans, and strings.
    const TOTAL: Self = Self {
        eq: true,
        partial_ord: true,
        ord: true,
    };
    /// `PartialOrd` only, as implemented by floats.
    const PARTIAL: Self = Self {
        eq: false,
        partial_ord: true,
        ord: false,
    };
    /// `Eq` without any ordering, as implemented by `serde_json::Value`.
    const EQ_ONLY: Self = Self {
        eq: true,
        partial_ord: false,
        ord: false,
    };

    /// Narrows to the traits both `self` and `other` implement.
    fn and(self, other: Self) -> Self {
        Self {
            eq: self.eq && other.eq,
            partial_ord: self.partial_ord && other.partial_ord,
            ord: self.ord && other.ord,
        }
    }
}

/// The Rust type generated for one template argument.
struct RustType {
    tokens: proc_macro2::TokenStream,
    /// Whether the type borrows from the deserialized input and therefore
    /// needs the enum's lifetime parameter.
    borrows: bool,
    comparisons: Comparisons,
}

impl RustType {
    /// An owned type with a total order.
    fn owned(tokens: proc_macro2::TokenStream) -> Self {
        Self {
            tokens,
            borrows: false,
            comparisons: Comparisons::TOTAL,
        }
    }
}

trait IntoRustType {
    fn into_rust_type(self) -> RustType;
}

impl IntoRustType for model::ArgumentType {
    fn into_rust_type(self) -> RustType {
        match self {
            Self::Number | Self::Integer => RustType::owned(quote! {i64}),
            Self::Float => RustType {
                tokens: quote! {f64},
                borrows: false,
                comparisons: Comparisons::PARTIAL,
            },
            Self::Boolean => RustType::owned(quote! {bool}),
            // Keep ISO 8601 values as strings so generated bindings do not
            // impose a date-time crate.
            Self::String | Self::Iso8601DateTimeString => RustType {
                tokens: quote! {&'a str},
                borrows: true,
                comparisons: Comparisons::TOTAL,
            },
            Self::Any => RustType {
                tokens: quote! {serde_json::Value},
                borrows: false,
                comparisons: Comparisons::EQ_ONLY,
            },
        }
    }
}

/// A collision between translation keys that map to one Rust enum identifier.
#[derive(thiserror::Error, Debug)]
pub struct DuplicateIdentifierError {
    identifier: String,
    keys: Vec<String>,
}

impl std::fmt::Display for DuplicateIdentifierError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "duplicate identifier `{}` (used by {})",
            self.identifier,
            self.keys.join(", ")
        )
    }
}

/// A collision between translation arguments that map to one Rust field name.
#[derive(thiserror::Error, Debug)]
pub struct DuplicateFieldError {
    field: String,
    enum_variant: String,
    arguments: Vec<String>,
    key: String,
}

impl std::fmt::Display for DuplicateFieldError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "{}: duplicate field `{}` used by arguments {} of variant `{}`",
            self.key,
            self.field,
            self.arguments
                .iter()
                .map(|arg| format!("{arg:?}"))
                .collect::<Vec<_>>()
                .join(", "),
            self.enum_variant,
        )
    }
}

/// Errors that can occur while generating Rust translation bindings.
#[derive(thiserror::Error, Debug)]
pub enum Error {
    /// Duplicate Rust enum identifier derived from translation keys.
    #[error(transparent)]
    DuplicateIdentifier(#[from] DuplicateIdentifierError),
    /// Duplicate Rust struct field derived from translation arguments.
    #[error(transparent)]
    DuplicateField(#[from] DuplicateFieldError),
    /// Error originating from the `syn` crate when pretty-printing generated code.
    #[error("{0}")]
    Syn(String),
}

/// One generated enum variant together with the properties of its fields.
struct Variant {
    tokens: proc_macro2::TokenStream,
    /// Whether any field borrows from the deserialized input.
    borrows: bool,
    /// The comparison traits every field implements.
    comparisons: Comparisons,
}

/// Generates the enum variant for one translation, rejecting argument names
/// that normalize to the same field.
fn generate_variant(
    safe_key: &str,
    key: &str,
    translation: &model::Translation,
) -> Result<Variant, Error> {
    use itertools::Itertools;

    let fields: Vec<_> = translation
        .arguments
        .iter()
        .map(|(name, typ)| (argument_to_rust_field_name(name), name, typ))
        .collect();

    let duplicates: Vec<_> = fields
        .iter()
        .duplicates_by(|(safe_name, _, _)| safe_name)
        .collect();

    if let Some(first) = duplicates.first() {
        let field = first.0.clone();
        let arguments = duplicates
            .into_iter()
            .map(|(_, key, _)| (*key).clone())
            .collect();
        return Err(Error::from(DuplicateFieldError {
            field,
            arguments,
            enum_variant: safe_key.to_string(),
            key: key.to_string(),
        }));
    }

    let mut borrows = false;
    let mut comparisons = Comparisons::TOTAL;
    let fields: Vec<_> = fields
        .into_iter()
        .map(|(safe_name, name, typ)| {
            let field_ident = format_ident!("{safe_name}");
            let typ = typ.into_rust_type();
            borrows |= typ.borrows;
            comparisons = comparisons.and(typ.comparisons);
            let typ = typ.tokens;
            quote! {
                #[serde(rename = #name)]
                #field_ident: #typ,
            }
        })
        .collect();

    let variant_name_ident = format_ident!("{safe_key}");
    let tokens = quote! {
        #variant_name_ident {
            #(#fields)*
        },
    };
    Ok(Variant {
        tokens,
        borrows,
        comparisons,
    })
}

/// Generates a Rust `Translation` enum for the given translations.
///
/// The generated code includes a `key` method that maps each variant back to
/// its original translation key.
///
/// # Errors
///
/// Returns an error if translation keys or argument names would result in
/// duplicate Rust identifiers, or if the generated code cannot be parsed by
/// `syn` for pretty-printing.
pub fn generate_translation_enum(translations: &model::Translations) -> Result<String, Error> {
    use itertools::Itertools;

    // Normalize every translation key to its generated variant name.
    let enum_variant_names: Vec<_> = translations
        .0
        .iter()
        .map(|(key, translation)| (key_to_rust_enum_variant(key.as_ref()), key, translation))
        .collect();

    // Reject collisions before generating an ambiguous enum.
    let duplicates: Vec<_> = enum_variant_names
        .iter()
        .duplicates_by(|(safe_key, _, _)| safe_key)
        .collect();

    if let Some(first) = duplicates.first() {
        let identifier = first.0.clone();
        let keys = duplicates
            .into_iter()
            .map(|(_, key, _)| key.to_string())
            .collect();
        return Err(DuplicateIdentifierError { identifier, keys }.into());
    }

    // Generate each variant, tracking what the enum as a whole can derive.
    let mut uses_lifetime = false;
    let mut comparisons = Comparisons::TOTAL;
    let mut enum_variants = Vec::with_capacity(enum_variant_names.len());
    for (safe_key, key, translation) in &enum_variant_names {
        let variant = generate_variant(safe_key, key.as_ref(), translation)?;
        uses_lifetime |= variant.borrows;
        comparisons = comparisons.and(variant.comparisons);
        enum_variants.push(variant.tokens);
    }

    // Build the reverse mapping from generated variants to translation keys.
    let enum_variant_keys: Vec<_> = enum_variant_names
        .iter()
        .map(|(safe_key, key, _)| {
            let variant_name_ident = format_ident!("{safe_key}");
            let key = key.as_ref();
            quote! {
                Self::#variant_name_ident { .. } => #key,
            }
        })
        .collect();

    // Introduce a lifetime only when at least one generated field borrows text.
    let generics: syn::Generics = if uses_lifetime {
        syn::parse_quote!(<'a>)
    } else {
        syn::Generics::default()
    };
    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

    // Derive only the comparisons every field supports: floats have no total
    // order and `serde_json::Value` has no order at all.
    let eq = comparisons.eq.then(|| quote! { Eq, });
    let partial_ord = comparisons.partial_ord.then(|| quote! { PartialOrd, });
    let ord = comparisons.ord.then(|| quote! { Ord, });

    let out = quote! {
        #[derive(
            Debug, Clone, PartialEq, #eq #partial_ord #ord ::serde::Serialize, ::serde::Deserialize,
        )]
        #[serde(untagged)]
        pub enum Translation #generics {
            #(#enum_variants)*
        }

        impl #impl_generics Translation #ty_generics #where_clause {
            pub fn key(&self) -> &'static str {
                match self {
                    #(#enum_variant_keys)*
                }
            }
        }
    };

    // Render and format the complete generated source file.
    let code = pretty_print(&out).map_err(|err| Error::Syn(err.to_string()))?;
    let code = format!("{}\n{}", preamble(), code);
    Ok(code)
}

fn pretty_print<T>(input: T) -> Result<String, syn::Error>
where
    T: quote::ToTokens,
{
    let file: syn::File = syn::parse2(quote! { #input })?;
    Ok(prettyplease::unparse(&file))
}

#[cfg(test)]
mod tests {
    use color_eyre::eyre;
    use globetrotter_model::{self as model, diagnostics::Spanned};
    use similar_asserts::assert_eq as sim_assert_eq;

    /// String arguments introduce a lifetime on the generated enum, and an
    /// `any` argument drops the ordering derives `serde_json::Value` lacks.
    #[test_util::test]
    fn generate_enum_with_lifetime() -> eyre::Result<()> {
        let translations = [
            (
                Spanned::dummy("test.one".to_string()),
                model::Translation {
                    language: [(
                        model::Language::En,
                        Spanned::dummy("test.one in en".to_string()),
                    )]
                    .into_iter()
                    .collect(),
                    arguments: [].into_iter().collect(),
                    file_id: 0,
                    allow: std::collections::BTreeSet::new(),
                },
            ),
            (
                Spanned::dummy("test.two".to_string()),
                model::Translation {
                    language: [(
                        model::Language::En,
                        Spanned::dummy("test.two in en".to_string()),
                    )]
                    .into_iter()
                    .collect(),
                    arguments: [
                        ("arg-one".to_string(), model::ArgumentType::String),
                        ("ArgTwo".to_string(), model::ArgumentType::Number),
                        ("Arg_Three".to_string(), model::ArgumentType::Any),
                        ("ArgFour".to_string(), model::ArgumentType::Boolean),
                        ("ArgFive".to_string(), model::ArgumentType::Integer),
                    ]
                    .into_iter()
                    .collect(),
                    file_id: 0,
                    allow: std::collections::BTreeSet::new(),
                },
            ),
        ];
        let translations = model::Translations(translations.into_iter().collect());
        let have = super::generate_translation_enum(&translations)?;
        println!("{have}");

        let want = indoc::indoc! {r#"
            #[derive(Debug, Clone, PartialEq, Eq, ::serde::Serialize, ::serde::Deserialize)]
            #[serde(untagged)]
            pub enum Translation<'a> {
                TestOne {},
                TestTwo {
                    #[serde(rename = "arg-one")]
                    arg_one: &'a str,
                    #[serde(rename = "ArgTwo")]
                    arg_two: i64,
                    #[serde(rename = "Arg_Three")]
                    arg_three: serde_json::Value,
                    #[serde(rename = "ArgFour")]
                    arg_four: bool,
                    #[serde(rename = "ArgFive")]
                    arg_five: i64,
                },
            }
            impl<'a> Translation<'a> {
                pub fn key(&self) -> &'static str {
                    match self {
                        Self::TestOne { .. } => "test.one",
                        Self::TestTwo { .. } => "test.two",
                    }
                }
            }
        "# };
        let want = format!("{}\n{}", super::preamble(), want);
        sim_assert_eq!(have: have, want: want);
        Ok(())
    }

    /// Float arguments keep `PartialOrd` but cannot derive `Eq` or `Ord`.
    #[test_util::test]
    fn generate_enum_with_float() -> eyre::Result<()> {
        let translations = [(
            Spanned::dummy("cart.total".to_string()),
            model::Translation {
                language: [(
                    model::Language::En,
                    Spanned::dummy("{{count}} items for {{price}}".to_string()),
                )]
                .into_iter()
                .collect(),
                arguments: [
                    ("count".to_string(), model::ArgumentType::Integer),
                    ("price".to_string(), model::ArgumentType::Float),
                ]
                .into_iter()
                .collect(),
                file_id: 0,
                allow: std::collections::BTreeSet::new(),
            },
        )];
        let translations = model::Translations(translations.into_iter().collect());
        let have = super::generate_translation_enum(&translations)?;
        println!("{have}");

        let want = indoc::indoc! {r#"
            #[derive(Debug, Clone, PartialEq, PartialOrd, ::serde::Serialize, ::serde::Deserialize)]
            #[serde(untagged)]
            pub enum Translation {
                CartTotal {
                    #[serde(rename = "count")]
                    count: i64,
                    #[serde(rename = "price")]
                    price: f64,
                },
            }
            impl Translation {
                pub fn key(&self) -> &'static str {
                    match self {
                        Self::CartTotal { .. } => "cart.total",
                    }
                }
            }
        "# };
        let want = format!("{}\n{}", super::preamble(), want);
        sim_assert_eq!(have: have, want: want);
        Ok(())
    }

    /// Owned argument types produce an enum without unused generics.
    #[test_util::test]
    fn generate_enum_without_lifetime() -> eyre::Result<()> {
        let translations = [
            (
                Spanned::dummy("test.one".to_string()),
                model::Translation {
                    language: [(
                        model::Language::En,
                        Spanned::dummy("test.one in en".to_string()),
                    )]
                    .into_iter()
                    .collect(),
                    arguments: [].into_iter().collect(),
                    file_id: 0,
                    allow: std::collections::BTreeSet::new(),
                },
            ),
            (
                Spanned::dummy("test.two".to_string()),
                model::Translation {
                    language: [(
                        model::Language::En,
                        Spanned::dummy("test.two in en".to_string()),
                    )]
                    .into_iter()
                    .collect(),
                    arguments: [("ArgTwo".to_string(), model::ArgumentType::Number)]
                        .into_iter()
                        .collect(),
                    file_id: 0,
                    allow: std::collections::BTreeSet::new(),
                },
            ),
        ];
        let translations = model::Translations(translations.into_iter().collect());
        let have = super::generate_translation_enum(&translations)?;
        println!("{have}");

        let want = indoc::indoc! {r#"
            #[derive(
                Debug,
                Clone,
                PartialEq,
                Eq,
                PartialOrd,
                Ord,
                ::serde::Serialize,
                ::serde::Deserialize,
            )]
            #[serde(untagged)]
            pub enum Translation {
                TestOne {},
                TestTwo { #[serde(rename = "ArgTwo")] arg_two: i64 },
            }
            impl Translation {
                pub fn key(&self) -> &'static str {
                    match self {
                        Self::TestOne { .. } => "test.one",
                        Self::TestTwo { .. } => "test.two",
                    }
                }
            }
        "# };
        let want = format!("{}\n{}", super::preamble(), want);
        sim_assert_eq!(have: have, want: want);
        Ok(())
    }
}