ontogen-ts 0.1.4

//! Serde-attribute extraction on `syn::Attribute` lists.
//!
//! Phase-1 supports the rename family (`rename`, `rename_all`,
//! `rename_all_fields`, `skip`) plus `default` at either scope (which maps
//! to a TS-optional `?` — on a field for that field, on a struct for every
//! field) and field-level
//! `flatten` (which maps to a TS intersection member — see
//! [`crate::emit::emit_struct_named`]), and rejects the remaining
//! shape-changing attrs (`tag`, `content`, `untagged`) plus split-rename
//! (`rename(serialize = "...", deserialize = "...")`) with an
//! [`EmitError::UnsupportedSerdeAttr`] carrying a hint at the symmetric form
//! or `#[ontogen::ts_opaque]`. Other serde attrs that don't change TS shape
//! (`borrow`, `bound`, `with`, `serialize_with`, etc.) are silently ignored.
//!
//! Each extractor handles an attribute at the level where serde itself
//! gives it meaning, and rejects it elsewhere. `tag`/`content`/`untagged`
//! are container attrs, so the field extractor rejects them; `flatten` is a
//! field attr, so the container and variant extractors reject it. (An
//! earlier revision listed `flatten` alongside the container attrs and
//! consulted the list only at container level, where serde forbids
//! `flatten` outright — so field-level `flatten` was silently ignored and
//! emitted TS that disagreed with the wire.)
//!
//! The same care applies to the rename family, where serde overloads one
//! spelling across two axes. On an enum, `rename_all` renames the
//! *variants*; `rename_all_fields` renames the fields inside every struct
//! variant; and `rename_all` on an individual *variant* renames that
//! variant's fields. They are kept in three separate slots
//! ([`ContainerAttrs::rename_all`], [`ContainerAttrs::rename_all_fields`],
//! [`VariantAttrs::rename_all`]) precisely so the emitter cannot apply one
//! where serde applies another.
//!
//! Parsing uses [`syn::Attribute::parse_nested_meta`] — the same primitive
//! `serde_derive`'s own parser uses — so the exact syntax we accept matches
//! what serde itself accepts.

use crate::types::{EmitError, RenameAll, TypePath};

/// Attributes on a container (struct or enum).
#[derive(Debug, Clone, Default)]
pub(crate) struct ContainerAttrs {
    /// `#[serde(rename_all = "...")]`.
    pub rename_all: Option<RenameAll>,
    /// `#[serde(rename = "...")]` on the container itself — overrides the
    /// container's TS name. Phase-1 emits structs/enums under their Rust
    /// ident; this field is parsed so future PRs can act on it.
    pub rename: Option<String>,
    /// `#[serde(rename_all_fields = "...")]` (serde 1.0.181+). Enums only:
    /// it renames the *fields of every struct variant*, which is a
    /// different axis from [`Self::rename_all`] (which on an enum renames
    /// the variants themselves). Kept separate so the emitter can't confuse
    /// the two.
    pub rename_all_fields: Option<RenameAll>,
    /// `#[serde(default)]` (or `default = "path::to::fn"`) on a struct. Any
    /// field absent from the input is taken from the struct's `Default`, so
    /// *every* field is optional on the wire and the emitter renders them
    /// all as `field?: T`.
    ///
    /// Serde only accepts this on a struct with named fields; on an enum it
    /// is a compile error, so [`crate::emit::emit_enum_named`] ignores it.
    pub default: bool,
}

/// Attributes on a struct field.
#[derive(Debug, Clone, Default)]
pub(crate) struct FieldAttrs {
    /// `#[serde(rename = "...")]` on the field.
    pub rename: Option<String>,
    /// `#[serde(skip)]` (or `skip_serializing` / `skip_deserializing` — any of
    /// the three drops the field from TS emission since we can't represent a
    /// field that's serialized but not deserialized as a single TS type).
    pub skip: bool,
    /// `#[serde(default)]` or `#[serde(default = "path::to::fn")]`. The
    /// deserializer substitutes a default when the field is absent, so the
    /// wire contract treats the field as optional — the emitter renders it as
    /// a TS-optional `field?: T`.
    pub default: bool,
    /// `#[serde(flatten)]`. The field's own name never reaches the wire —
    /// its type's keys are spliced into the parent object — so the emitter
    /// renders it as a TS intersection member rather than a property.
    pub flatten: bool,
}

/// Attributes on an enum variant.
#[derive(Debug, Clone, Default)]
pub(crate) struct VariantAttrs {
    /// `#[serde(rename = "...")]` on the variant.
    pub rename: Option<String>,
    /// `#[serde(skip)]`.
    pub skip: bool,
    /// `#[serde(rename_all = "...")]` on the variant. Renames *this
    /// variant's* struct fields — it does not touch the variant's own wire
    /// name, which comes from the enum's `rename_all` and this variant's
    /// `rename`. Overrides the container's `rename_all_fields`.
    pub rename_all: Option<RenameAll>,
}

impl RenameAll {
    /// Parse a serde `rename_all` literal (the string after `=`) into a
    /// [`RenameAll`] variant. Returns `None` if the literal isn't one of
    /// serde's eight recognized modes.
    pub(crate) fn from_serde_str(s: &str) -> Option<Self> {
        Some(match s {
            "lowercase" => Self::Lowercase,
            "UPPERCASE" => Self::Uppercase,
            "PascalCase" => Self::PascalCase,
            "camelCase" => Self::CamelCase,
            "snake_case" => Self::SnakeCase,
            "SCREAMING_SNAKE_CASE" => Self::ScreamingSnakeCase,
            "kebab-case" => Self::KebabCase,
            "SCREAMING-KEBAB-CASE" => Self::ScreamingKebabCase,
            _ => return None,
        })
    }
}

/// Container-level serde attrs that ontogen-ts rejects outright as
/// "shape-changing serde attributes" — these alter the JSON wire shape in
/// ways that need a dedicated emission path (phase 2 / OF-015 phase 2).
///
/// `flatten` is deliberately NOT in this list: it is a *field* attribute
/// with its own [`MetaKind::Flatten`] classification and a real emission
/// path (a TS intersection member). Anything listed here is rejected at
/// every level — all three are container attrs, so an occurrence on a field
/// or variant is a malformed input serde itself would refuse.
const REJECTED_SHAPE_ATTRS: &[&str] = &["tag", "content", "untagged"];

/// Shared tail for the "shape-changing container attr" rejection message.
const REJECTED_SHAPE_HINT: &str = "shape-changing attrs (tag/content/untagged) are phase 2 work; use \
                                   #[ontogen::ts_opaque(target = \"...\")] if a custom TS rendering is needed";

/// Ontogen-specific attributes on a type definition. Both attrs are
/// no-ops at Rust compile time (the proc-macro implementations in
/// `ontogen-macros` pass the annotated item through unchanged); ontogen-ts
/// reads them via this extractor during scanning.
#[derive(Debug, Clone, Default)]
pub(crate) struct OntogenAttrs {
    /// `#[ts_opaque(target = "...")]` — emitter treats the type as terminal
    /// and emits `target` verbatim at every reference site.
    pub ts_opaque: Option<String>,
    /// `#[ts_name = "..."]` — overrides the TS name emitted for the type.
    /// JSON wire is unaffected.
    pub ts_name: Option<String>,
}

/// Extract `#[ts_opaque(target = "...")]` and `#[ts_name = "..."]` from a
/// `&[syn::Attribute]`. Matches on the terminal segment of the attribute
/// path so the attrs work whether imported bare, via `ontogen_macros::`,
/// or via `ontogen::` (the umbrella re-export).
pub(crate) fn extract_ontogen_attrs(
    attrs: &[syn::Attribute],
    referenced_by: &TypePath,
) -> Result<OntogenAttrs, EmitError> {
    let mut out = OntogenAttrs::default();
    for attr in attrs {
        let terminal = match attr.path().segments.last() {
            Some(seg) => seg.ident.to_string(),
            None => continue,
        };
        match terminal.as_str() {
            "ts_opaque" => {
                // Shape: `#[ts_opaque(target = "literal")]`. The macro
                // validates this at Rust compile time, so we expect a
                // well-formed input — but parse defensively.
                let mut target: Option<String> = None;
                attr.parse_nested_meta(|meta| {
                    if meta.path.is_ident("target") {
                        let value = meta.value()?;
                        let lit: syn::LitStr = value.parse()?;
                        target = Some(lit.value());
                        Ok(())
                    } else {
                        Err(meta.error("ts_opaque expects `target = \"...\"`"))
                    }
                })
                .map_err(|err| EmitError::UnsupportedSerdeAttr {
                    type_path: referenced_by.clone(),
                    attr: format!("could not parse #[ts_opaque(...)]: {err}"),
                })?;
                out.ts_opaque = target;
            }
            "ts_name" => {
                // Shape: `#[ts_name = "literal"]` (bare string literal arg).
                let value = match &attr.meta {
                    syn::Meta::NameValue(nv) => &nv.value,
                    _ => {
                        return Err(EmitError::UnsupportedSerdeAttr {
                            type_path: referenced_by.clone(),
                            attr: "#[ts_name = \"...\"] expects the `= \"literal\"` form".to_string(),
                        });
                    }
                };
                let lit = match value {
                    syn::Expr::Lit(expr_lit) => match &expr_lit.lit {
                        syn::Lit::Str(s) => s.value(),
                        _ => {
                            return Err(EmitError::UnsupportedSerdeAttr {
                                type_path: referenced_by.clone(),
                                attr: "#[ts_name = ...] value must be a string literal".to_string(),
                            });
                        }
                    },
                    _ => {
                        return Err(EmitError::UnsupportedSerdeAttr {
                            type_path: referenced_by.clone(),
                            attr: "#[ts_name = ...] value must be a string literal".to_string(),
                        });
                    }
                };
                out.ts_name = Some(lit);
            }
            _ => {}
        }
    }
    Ok(out)
}

/// Parse a `rename_all`-family literal into a [`RenameAll`], naming the
/// offending attribute in the error so `rename_all` and `rename_all_fields`
/// are distinguishable in a build log.
fn parse_rename_all(value: &str, attr_name: &str, referenced_by: &TypePath) -> Result<RenameAll, EmitError> {
    RenameAll::from_serde_str(value).ok_or_else(|| EmitError::UnsupportedSerdeAttr {
        type_path: referenced_by.clone(),
        attr: format!("{attr_name} = \"{value}\" (not one of serde's eight recognized modes)"),
    })
}

/// Extract container-level serde attributes (struct or enum).
pub(crate) fn extract_container_attrs(
    attrs: &[syn::Attribute],
    referenced_by: &TypePath,
) -> Result<ContainerAttrs, EmitError> {
    let mut out = ContainerAttrs::default();
    for attr in attrs {
        if !attr.path().is_ident("serde") {
            continue;
        }
        walk_serde(attr, |meta_kind| {
            match meta_kind {
                MetaKind::RenameLit(value) => {
                    out.rename = Some(value);
                    Ok(())
                }
                MetaKind::RenameAllLit(value) => {
                    out.rename_all = Some(parse_rename_all(&value, "rename_all", referenced_by)?);
                    Ok(())
                }
                MetaKind::RenameAllFieldsLit(value) => {
                    out.rename_all_fields = Some(parse_rename_all(&value, "rename_all_fields", referenced_by)?);
                    Ok(())
                }
                MetaKind::SplitRename | MetaKind::SplitRenameAll => Err(EmitError::UnsupportedSerdeAttr {
                    type_path: referenced_by.clone(),
                    attr: "split-rename (rename(serialize = \"...\", deserialize = \"...\")) is not supported in \
                           phase 1 — use the symmetric form #[serde(rename = \"...\")] or \
                           #[ontogen::ts_opaque(target = \"...\")] if the serde asymmetry must be preserved for \
                           non-ontogen-ts consumers"
                        .to_string(),
                }),
                MetaKind::RejectedShape(name) => Err(EmitError::UnsupportedSerdeAttr {
                    type_path: referenced_by.clone(),
                    attr: format!("serde({name}) — {REJECTED_SHAPE_HINT}"),
                }),
                // serde only accepts `flatten` on a field. Seeing it here
                // means the source wouldn't compile; say so rather than
                // ignoring it.
                MetaKind::Flatten => Err(EmitError::UnsupportedSerdeAttr {
                    type_path: referenced_by.clone(),
                    attr: "serde(flatten) is a field attribute — serde does not accept it on a struct or enum \
                           declaration"
                        .to_string(),
                }),
                MetaKind::Skip => Ok(()), // ignore at container level
                // Container-level `#[serde(default)]` fills every absent field
                // from the struct's `Default`, so the whole body is optional
                // on the wire. Record it; `emit_struct_named` marks each field
                // TS-optional.
                MetaKind::Default => {
                    out.default = true;
                    Ok(())
                }
                MetaKind::Unknown => Ok(()),
            }
        })?;
    }
    Ok(out)
}

/// Extract field-level serde attributes.
pub(crate) fn extract_field_attrs(attrs: &[syn::Attribute], referenced_by: &TypePath) -> Result<FieldAttrs, EmitError> {
    let mut out = FieldAttrs::default();
    for attr in attrs {
        if !attr.path().is_ident("serde") {
            continue;
        }
        walk_serde(attr, |meta_kind| {
            match meta_kind {
                MetaKind::RenameLit(value) => {
                    out.rename = Some(value);
                    Ok(())
                }
                // Neither is meaningful on a field: `rename_all` applies to a
                // container's members, `rename_all_fields` to an enum's
                // struct-variant fields.
                MetaKind::RenameAllLit(_) | MetaKind::RenameAllFieldsLit(_) => Ok(()),
                MetaKind::Skip => {
                    out.skip = true;
                    Ok(())
                }
                MetaKind::Default => {
                    out.default = true;
                    Ok(())
                }
                MetaKind::Flatten => {
                    out.flatten = true;
                    Ok(())
                }
                MetaKind::SplitRename => Err(EmitError::UnsupportedSerdeAttr {
                    type_path: referenced_by.clone(),
                    attr: "split-rename (rename(serialize = \"...\", deserialize = \"...\")) on a field is not \
                           supported in phase 1 — use the symmetric form #[serde(rename = \"...\")] or \
                           #[ontogen::ts_opaque(target = \"...\")] on the parent type"
                        .to_string(),
                }),
                // tag/content/untagged are container attrs; serde rejects
                // them on a field, so reaching this arm means the input is
                // malformed. Surface it rather than swallowing it.
                MetaKind::RejectedShape(name) => Err(EmitError::UnsupportedSerdeAttr {
                    type_path: referenced_by.clone(),
                    attr: format!("serde({name}) on a field — {REJECTED_SHAPE_HINT}"),
                }),
                MetaKind::SplitRenameAll | MetaKind::Unknown => Ok(()),
            }
        })?;
    }
    Ok(out)
}

/// Extract variant-level serde attributes.
pub(crate) fn extract_variant_attrs(
    attrs: &[syn::Attribute],
    referenced_by: &TypePath,
) -> Result<VariantAttrs, EmitError> {
    let mut out = VariantAttrs::default();
    for attr in attrs {
        if !attr.path().is_ident("serde") {
            continue;
        }
        walk_serde(attr, |meta_kind| match meta_kind {
            MetaKind::RenameLit(value) => {
                out.rename = Some(value);
                Ok(())
            }
            MetaKind::Skip => {
                out.skip = true;
                Ok(())
            }
            MetaKind::SplitRename => Err(EmitError::UnsupportedSerdeAttr {
                type_path: referenced_by.clone(),
                attr: "split-rename on a variant is not supported in phase 1 — use the symmetric form \
                           #[serde(rename = \"...\")]"
                    .to_string(),
            }),
            // `#[serde(untagged)]` is legal on an individual variant (serde
            // 1.0.181+) and changes that variant's wire shape; `tag`/`content`
            // are container-only. Either way we have no faithful rendering,
            // so reject rather than emit the externally-tagged default.
            MetaKind::RejectedShape(name) => Err(EmitError::UnsupportedSerdeAttr {
                type_path: referenced_by.clone(),
                attr: format!("serde({name}) on a variant — {REJECTED_SHAPE_HINT}"),
            }),
            // serde only accepts `flatten` on a field.
            MetaKind::Flatten => Err(EmitError::UnsupportedSerdeAttr {
                type_path: referenced_by.clone(),
                attr: "serde(flatten) is a field attribute — serde does not accept it on an enum variant".to_string(),
            }),
            // On a variant, `rename_all` governs THIS variant's struct
            // fields — not the variant's own wire name. Capture it so the
            // emitter can apply it where serde does.
            MetaKind::RenameAllLit(value) => {
                out.rename_all = Some(parse_rename_all(&value, "rename_all", referenced_by)?);
                Ok(())
            }
            // `rename_all_fields` is an enum-container attr; serde doesn't
            // accept it on a variant.
            MetaKind::RenameAllFieldsLit(_) | MetaKind::SplitRenameAll | MetaKind::Default | MetaKind::Unknown => {
                Ok(())
            }
        })?;
    }
    Ok(out)
}

/// Classified shape of a single nested serde meta item.
enum MetaKind {
    /// `rename = "wireName"` — symmetric.
    RenameLit(String),
    /// `rename_all = "camelCase"` — symmetric.
    RenameAllLit(String),
    /// `rename_all_fields = "camelCase"` — symmetric. Enum containers only.
    RenameAllFieldsLit(String),
    /// `rename(serialize = "...", deserialize = "...")` — rejected.
    SplitRename,
    /// `rename_all(serialize = "...", deserialize = "...")` — rejected.
    SplitRenameAll,
    /// `tag`, `content`, `untagged` — rejected at every level.
    RejectedShape(String),
    /// `flatten` — supported on a field (TS intersection member), rejected
    /// on a container or variant where serde itself wouldn't accept it.
    Flatten,
    /// `skip`, `skip_serializing`, `skip_deserializing` — fold all three.
    Skip,
    /// `default` or `default = "path::to::fn"` — field is optional on the wire.
    Default,
    /// Anything we don't recognize is silently ignored.
    Unknown,
}

/// Helper for the outer walker: when an unknown / split-form inner meta has
/// a `= "lit"` value, consume the literal so the outer parser keeps going.
/// Used as the callback to `meta.parse_nested_meta(...)` when the outer code
/// doesn't care about the inner contents.
fn consume_inner_value(inner: syn::meta::ParseNestedMeta<'_>) -> syn::Result<()> {
    if let Ok(value) = inner.value() {
        let _: syn::Lit = value.parse()?;
    }
    Ok(())
}

/// Walk a `#[serde(...)]` attribute and call `f` on each classified nested
/// meta. Each invocation of `f` can return `Err(EmitError)` to short-circuit.
fn walk_serde<F>(attr: &syn::Attribute, mut f: F) -> Result<(), EmitError>
where
    F: FnMut(MetaKind) -> Result<(), EmitError>,
{
    // We collect both classification + any classifier-level EmitError, then
    // dispatch outside the parse_nested_meta closure (its return type is
    // syn::Result, not Result<_, EmitError>).
    let mut callbacks: Vec<MetaKind> = Vec::new();
    let parse_result = attr.parse_nested_meta(|meta| {
        let ident = match meta.path.get_ident() {
            Some(id) => id.to_string(),
            None => {
                callbacks.push(MetaKind::Unknown);
                return Ok(());
            }
        };
        match ident.as_str() {
            "rename" => {
                // Two shapes: `rename = "lit"` (symmetric) or `rename(...)`
                // (split). `meta.value()` returns Ok iff the next token is
                // `=`; an `Err` here means we're looking at the list form.
                match meta.value() {
                    Ok(value) => {
                        let lit: syn::LitStr = value.parse().map_err(|_| meta.error("expected string literal"))?;
                        callbacks.push(MetaKind::RenameLit(lit.value()));
                    }
                    Err(_) => {
                        // List form — split-rename. Consume the parens AND
                        // each inner `serialize = "..."` / `deserialize = "..."`
                        // so the outer parser doesn't choke. We don't care
                        // about the contents.
                        meta.parse_nested_meta(consume_inner_value)?;
                        callbacks.push(MetaKind::SplitRename);
                    }
                }
                Ok(())
            }
            // Same two shapes as `rename`, and both attrs share the
            // split-form rejection — but they target different things, so
            // they classify separately. `rename_all` renames a container's
            // members; `rename_all_fields` renames the fields inside an
            // enum's struct variants.
            "rename_all" | "rename_all_fields" => {
                let is_fields = ident == "rename_all_fields";
                match meta.value() {
                    Ok(value) => {
                        let lit: syn::LitStr = value.parse().map_err(|_| meta.error("expected string literal"))?;
                        callbacks.push(if is_fields {
                            MetaKind::RenameAllFieldsLit(lit.value())
                        } else {
                            MetaKind::RenameAllLit(lit.value())
                        });
                    }
                    Err(_) => {
                        meta.parse_nested_meta(consume_inner_value)?;
                        callbacks.push(MetaKind::SplitRenameAll);
                    }
                }
                Ok(())
            }
            "skip" | "skip_serializing" | "skip_deserializing" => {
                callbacks.push(MetaKind::Skip);
                Ok(())
            }
            "default" => {
                // Two shapes: bare `default` (no value) or the path form
                // `default = "module::fn"`. Both mean the same thing for TS
                // emission — the field may be absent on the wire — so consume
                // the value if present and classify both as `Default`.
                if let Ok(value) = meta.value() {
                    let _: syn::LitStr = value.parse().map_err(|_| meta.error("expected string literal"))?;
                }
                callbacks.push(MetaKind::Default);
                Ok(())
            }
            "flatten" => {
                // Serde's `flatten` is a bare word; be tolerant of a value
                // anyway so a malformed attr doesn't desync the parser.
                if let Ok(value) = meta.value() {
                    let _: syn::Lit = value.parse().map_err(|_| meta.error("expected literal"))?;
                }
                callbacks.push(MetaKind::Flatten);
                Ok(())
            }
            other if REJECTED_SHAPE_ATTRS.contains(&other) => {
                // These attrs may carry values; consume them if present so the
                // parser doesn't bail out.
                if let Ok(value) = meta.value() {
                    let _: syn::LitStr = value.parse().map_err(|_| meta.error("expected string literal"))?;
                }
                callbacks.push(MetaKind::RejectedShape(other.to_string()));
                Ok(())
            }
            _ => {
                // Unknown attr — consume any value or nested list form so the
                // outer parser stays in sync.
                if let Ok(value) = meta.value() {
                    let _: syn::Lit = value.parse().map_err(|_| meta.error("expected literal"))?;
                } else {
                    let _ = meta.parse_nested_meta(consume_inner_value);
                }
                callbacks.push(MetaKind::Unknown);
                Ok(())
            }
        }
    });
    if let Err(err) = parse_result {
        // syn parse errors on serde attrs are pretty rare in practice (well-
        // formed Rust source means the attribute parsed; this branch fires
        // only when serde syntax is malformed). Bubble it up as a generic
        // EmitError so callers can show the user where the problem is.
        return Err(EmitError::UnsupportedSerdeAttr {
            type_path: TypePath::new(vec!["<unknown>".to_string()]).expect("non-empty"),
            attr: format!("could not parse #[serde(...)]: {err}"),
        });
    }
    for cb in callbacks {
        f(cb)?;
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::{EmitError, TypePath};

    fn tp(name: &str) -> TypePath {
        TypePath::new(vec![name.to_string()]).expect("non-empty")
    }

    /// Parse a struct from source and return its attrs.
    fn struct_attrs(src: &str) -> Vec<syn::Attribute> {
        let item: syn::ItemStruct = syn::parse_str(src).expect("parse struct");
        item.attrs
    }

    /// Parse an enum from source and return its attrs.
    fn enum_attrs(src: &str) -> Vec<syn::Attribute> {
        let item: syn::ItemEnum = syn::parse_str(src).expect("parse enum");
        item.attrs
    }

    /// Parse the first named field of a struct and return its attrs.
    fn first_field_attrs(src: &str) -> Vec<syn::Attribute> {
        let item: syn::ItemStruct = syn::parse_str(src).expect("parse struct");
        let syn::Fields::Named(named) = item.fields else {
            panic!("test fixture must use named fields");
        };
        named.named.into_iter().next().expect("at least one field").attrs
    }

    /// Parse the first variant of an enum and return its attrs.
    fn first_variant_attrs(src: &str) -> Vec<syn::Attribute> {
        let item: syn::ItemEnum = syn::parse_str(src).expect("parse enum");
        item.variants.into_iter().next().expect("at least one variant").attrs
    }

    // ── Container: rename_all ─────────────────────────────────────────────

    #[test]
    fn container_rename_all_camel_case() {
        let attrs = struct_attrs(
            r#"
            #[serde(rename_all = "camelCase")]
            struct Foo { a: u32 }
            "#,
        );
        let out = extract_container_attrs(&attrs, &tp("Foo")).unwrap();
        assert_eq!(out.rename_all, Some(RenameAll::CamelCase));
    }

    #[test]
    fn container_rename_all_all_eight_modes() {
        let pairs = [
            ("lowercase", RenameAll::Lowercase),
            ("UPPERCASE", RenameAll::Uppercase),
            ("PascalCase", RenameAll::PascalCase),
            ("camelCase", RenameAll::CamelCase),
            ("snake_case", RenameAll::SnakeCase),
            ("SCREAMING_SNAKE_CASE", RenameAll::ScreamingSnakeCase),
            ("kebab-case", RenameAll::KebabCase),
            ("SCREAMING-KEBAB-CASE", RenameAll::ScreamingKebabCase),
        ];
        for (src, expected) in pairs {
            let attrs = struct_attrs(&format!(r#"#[serde(rename_all = "{src}")] struct Foo {{ a: u32 }}"#));
            let out = extract_container_attrs(&attrs, &tp("Foo")).unwrap();
            assert_eq!(out.rename_all, Some(expected), "rename_all = \"{src}\"");
        }
    }

    #[test]
    fn container_rename_all_unknown_mode_rejected() {
        let attrs = struct_attrs(
            r#"
            #[serde(rename_all = "Train-Case")]
            struct Foo { a: u32 }
            "#,
        );
        let err = extract_container_attrs(&attrs, &tp("Foo")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("Train-Case"), "attr was: {attr}");
                assert!(attr.contains("recognized modes"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    #[test]
    fn container_split_rename_all_rejected() {
        let attrs = struct_attrs(
            r#"
            #[serde(rename_all(serialize = "camelCase", deserialize = "snake_case"))]
            struct Foo { a: u32 }
            "#,
        );
        let err = extract_container_attrs(&attrs, &tp("Foo")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("split-rename"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    // ── Container: tag/content/untagged/flatten rejected ──────────────────

    #[test]
    fn container_tag_rejected() {
        let attrs = enum_attrs(
            r#"
            #[serde(tag = "type")]
            enum Msg { Click, Hover }
            "#,
        );
        let err = extract_container_attrs(&attrs, &tp("Msg")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("tag"), "attr was: {attr}");
                assert!(attr.contains("phase 2"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    #[test]
    fn container_untagged_rejected() {
        let attrs = enum_attrs(
            r#"
            #[serde(untagged)]
            enum U { A(u32), B(String) }
            "#,
        );
        let err = extract_container_attrs(&attrs, &tp("U")).unwrap_err();
        assert!(matches!(err, EmitError::UnsupportedSerdeAttr { .. }));
    }

    // ── Field: rename ─────────────────────────────────────────────────────

    #[test]
    fn field_rename() {
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                #[serde(rename = "wireName")]
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert_eq!(out.rename.as_deref(), Some("wireName"));
        assert!(!out.skip);
    }

    #[test]
    fn field_skip() {
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                #[serde(skip)]
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert!(out.skip);
    }

    #[test]
    fn field_skip_serializing_treated_as_skip() {
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                #[serde(skip_serializing)]
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert!(out.skip);
    }

    #[test]
    fn field_split_rename_rejected() {
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                #[serde(rename(serialize = "wire_name", deserialize = "wireName"))]
                pub a: u32,
            }
            "#,
        );
        let err = extract_field_attrs(&attrs, &tp("Foo")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("split-rename"), "attr was: {attr}");
                assert!(attr.contains("on a field"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    #[test]
    fn field_no_serde_attrs_returns_default() {
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert!(out.rename.is_none());
        assert!(!out.skip);
    }

    #[test]
    fn field_default_bare_sets_flag() {
        // `#[serde(default)]` marks the field optional on the wire.
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                #[serde(default)]
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert!(out.default, "bare #[serde(default)] should set the default flag");
        assert!(out.rename.is_none());
        assert!(!out.skip);
    }

    #[test]
    fn field_default_path_form_sets_flag() {
        // `#[serde(default = "path")]` means the same thing for TS emission.
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                #[serde(default = "defaults::a")]
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert!(out.default, "path-form #[serde(default = \"...\")] should set the default flag");
    }

    #[test]
    fn field_without_default_leaves_flag_unset() {
        let attrs = first_field_attrs(
            r#"
            struct Foo {
                pub a: u32,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
        assert!(!out.default);
    }

    #[test]
    fn container_default_sets_flag() {
        // Container-level `#[serde(default)]` fills every absent field from
        // the struct's `Default`, so the emitter needs to know about it —
        // it used to be dropped here, and the whole body silently emitted as
        // required.
        let attrs = struct_attrs(
            r#"
            #[serde(default)]
            struct Foo { a: u32 }
            "#,
        );
        assert!(extract_container_attrs(&attrs, &tp("Foo")).unwrap().default);
    }

    #[test]
    fn container_default_path_form_sets_flag() {
        // `#[serde(default = "path")]` on a struct means the same thing.
        let attrs = struct_attrs(
            r#"
            #[serde(default = "defaults::foo")]
            struct Foo { a: u32 }
            "#,
        );
        assert!(extract_container_attrs(&attrs, &tp("Foo")).unwrap().default);
    }

    #[test]
    fn container_without_default_leaves_flag_unset() {
        let attrs = struct_attrs(
            r#"
            #[serde(rename_all = "camelCase")]
            struct Foo { a: u32 }
            "#,
        );
        assert!(!extract_container_attrs(&attrs, &tp("Foo")).unwrap().default);
    }

    // ── rename_all vs rename_all_fields (issue #133) ──────────────────────

    #[test]
    fn container_rename_all_fields_is_its_own_axis() {
        // Both attrs can appear together and must not overwrite each other:
        // one renames the enum's variants, the other its struct-variant
        // fields.
        let attrs = enum_attrs(
            r#"
            #[serde(rename_all = "camelCase", rename_all_fields = "SCREAMING_SNAKE_CASE")]
            enum Event { ToolCall { prompt_template: String } }
            "#,
        );
        let out = extract_container_attrs(&attrs, &tp("Event")).unwrap();
        assert_eq!(out.rename_all, Some(RenameAll::CamelCase));
        assert_eq!(out.rename_all_fields, Some(RenameAll::ScreamingSnakeCase));
    }

    #[test]
    fn container_rename_all_leaves_rename_all_fields_unset() {
        let attrs = enum_attrs(
            r#"
            #[serde(rename_all = "camelCase")]
            enum Event { ToolCall { prompt_template: String } }
            "#,
        );
        let out = extract_container_attrs(&attrs, &tp("Event")).unwrap();
        assert_eq!(out.rename_all, Some(RenameAll::CamelCase));
        assert_eq!(out.rename_all_fields, None, "rename_all must not imply rename_all_fields");
    }

    #[test]
    fn container_rename_all_fields_unknown_mode_names_the_right_attr() {
        let attrs = enum_attrs(
            r#"
            #[serde(rename_all_fields = "Train-Case")]
            enum Event { ToolCall { prompt_template: String } }
            "#,
        );
        match extract_container_attrs(&attrs, &tp("Event")).unwrap_err() {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("rename_all_fields"), "attr was: {attr}");
                assert!(attr.contains("Train-Case"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    #[test]
    fn variant_rename_all_is_captured() {
        // On a variant, `rename_all` targets that variant's fields. It used
        // to be dropped, so there was no way to express it.
        let attrs = first_variant_attrs(
            r#"
            enum Event {
                #[serde(rename_all = "camelCase")]
                ToolCall { prompt_template: String },
            }
            "#,
        );
        let out = extract_variant_attrs(&attrs, &tp("Event")).unwrap();
        assert_eq!(out.rename_all, Some(RenameAll::CamelCase));
        assert!(out.rename.is_none(), "rename_all must not set the variant's own wire name");
    }

    #[test]
    fn variant_rename_and_rename_all_are_independent() {
        let attrs = first_variant_attrs(
            r#"
            enum Event {
                #[serde(rename = "call", rename_all = "UPPERCASE")]
                ToolCall { prompt_template: String },
            }
            "#,
        );
        let out = extract_variant_attrs(&attrs, &tp("Event")).unwrap();
        assert_eq!(out.rename.as_deref(), Some("call"));
        assert_eq!(out.rename_all, Some(RenameAll::Uppercase));
    }

    #[test]
    fn field_rename_all_family_is_ignored() {
        // Neither attr means anything on a field.
        for src in ["rename_all = \"camelCase\"", "rename_all_fields = \"camelCase\""] {
            let attrs = first_field_attrs(&format!(
                r#"
                struct Foo {{
                    #[serde({src})]
                    pub prompt_template: String,
                }}
                "#
            ));
            let out = extract_field_attrs(&attrs, &tp("Foo")).unwrap();
            assert!(out.rename.is_none(), "src `{src}` should be inert on a field");
            assert!(!out.skip);
        }
    }

    // ── flatten: classified at the level where serde allows it ────────────

    #[test]
    fn field_flatten_sets_flag() {
        // Issue #132: `flatten` is a field attribute, so the field extractor
        // is the only place it can legally show up — and it must not be
        // swallowed there.
        let attrs = first_field_attrs(
            r#"
            struct Step {
                #[serde(flatten)]
                pub meta: StepMeta,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Step")).unwrap();
        assert!(out.flatten, "#[serde(flatten)] should set the flatten flag");
        assert!(out.rename.is_none());
        assert!(!out.skip);
        assert!(!out.default);
    }

    #[test]
    fn field_flatten_composes_with_default() {
        // Both flags are parsed; the emitter is what rejects the pairing.
        let attrs = first_field_attrs(
            r#"
            struct Step {
                #[serde(flatten, default)]
                pub meta: StepMeta,
            }
            "#,
        );
        let out = extract_field_attrs(&attrs, &tp("Step")).unwrap();
        assert!(out.flatten);
        assert!(out.default);
    }

    #[test]
    fn field_without_flatten_leaves_flag_unset() {
        let attrs = first_field_attrs(
            r#"
            struct Step {
                pub meta: StepMeta,
            }
            "#,
        );
        assert!(!extract_field_attrs(&attrs, &tp("Step")).unwrap().flatten);
    }

    #[test]
    fn container_flatten_rejected() {
        // Serde doesn't accept `flatten` on a container at all, so say that
        // rather than silently ignoring it.
        let attrs = struct_attrs(
            r#"
            #[serde(flatten)]
            struct Foo { a: u32 }
            "#,
        );
        let err = extract_container_attrs(&attrs, &tp("Foo")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("field attribute"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    #[test]
    fn variant_flatten_rejected() {
        let attrs = first_variant_attrs(
            r#"
            enum E {
                #[serde(flatten)]
                A,
            }
            "#,
        );
        let err = extract_variant_attrs(&attrs, &tp("E")).unwrap_err();
        assert!(matches!(err, EmitError::UnsupportedSerdeAttr { .. }));
    }

    #[test]
    fn field_level_container_shape_attrs_rejected() {
        // tag/content/untagged are container attrs. Reaching the field
        // extractor means the input is malformed; don't swallow it.
        for src in ["tag = \"type\"", "content = \"c\"", "untagged"] {
            let attrs = first_field_attrs(&format!(
                r#"
                struct Foo {{
                    #[serde({src})]
                    pub a: u32,
                }}
                "#
            ));
            let err = extract_field_attrs(&attrs, &tp("Foo")).unwrap_err();
            match err {
                EmitError::UnsupportedSerdeAttr { attr, .. } => {
                    assert!(attr.contains("on a field"), "src `{src}` — attr was: {attr}");
                }
                other => panic!("expected UnsupportedSerdeAttr for `{src}`, got {other:?}"),
            }
        }
    }

    #[test]
    fn variant_level_untagged_rejected() {
        // Variant-level `#[serde(untagged)]` is legal serde (1.0.181+) and
        // changes that variant's wire shape, so the externally-tagged
        // default we'd otherwise emit would be wrong.
        let attrs = first_variant_attrs(
            r#"
            enum U {
                #[serde(untagged)]
                Other(String),
            }
            "#,
        );
        let err = extract_variant_attrs(&attrs, &tp("U")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("on a variant"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    // ── Variant: rename ───────────────────────────────────────────────────

    #[test]
    fn variant_rename() {
        let attrs = first_variant_attrs(
            r#"
            enum Color {
                #[serde(rename = "rouge")]
                Red,
            }
            "#,
        );
        let out = extract_variant_attrs(&attrs, &tp("Color")).unwrap();
        assert_eq!(out.rename.as_deref(), Some("rouge"));
    }

    #[test]
    fn variant_split_rename_rejected() {
        let attrs = first_variant_attrs(
            r#"
            enum Color {
                #[serde(rename(serialize = "Red", deserialize = "red"))]
                Red,
            }
            "#,
        );
        let err = extract_variant_attrs(&attrs, &tp("Color")).unwrap_err();
        match err {
            EmitError::UnsupportedSerdeAttr { attr, .. } => {
                assert!(attr.contains("split-rename"), "attr was: {attr}");
                assert!(attr.contains("variant"), "attr was: {attr}");
            }
            other => panic!("expected UnsupportedSerdeAttr, got {other:?}"),
        }
    }

    // ── Combined: container + field interaction (parser side only) ────────

    #[test]
    fn container_rename_and_rename_all_both_parsed() {
        let attrs = struct_attrs(
            r#"
            #[serde(rename = "FooDto", rename_all = "camelCase")]
            struct Foo { a: u32 }
            "#,
        );
        let out = extract_container_attrs(&attrs, &tp("Foo")).unwrap();
        assert_eq!(out.rename.as_deref(), Some("FooDto"));
        assert_eq!(out.rename_all, Some(RenameAll::CamelCase));
    }
}