ruwuma/ruma-events-macros/src/event_enum.rs

//! Implementation of event enum and event content enum macros.

use matches::matches;
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote};
use syn::{
    parse::{self, Parse, ParseStream},
    Attribute, Expr, ExprLit, Ident, Lit, LitStr, Token,
};

fn is_non_stripped_room_event(kind: &EventKind, var: &EventKindVariation) -> bool {
    matches!(kind, EventKind::Message(_) | EventKind::State(_))
        && !matches!(var, EventKindVariation::Stripped | EventKindVariation::RedactedStripped)
}

fn has_prev_content_field(kind: &EventKind, var: &EventKindVariation) -> bool {
    matches!(kind, EventKind::State(_))
        && matches!(var, EventKindVariation::Full | EventKindVariation::Sync)
}

type EventKindFn = fn(&EventKind, &EventKindVariation) -> bool;

/// This const is used to generate the accessor methods for the `Any*Event` enums.
///
/// DO NOT alter the field names unless the structs in `ruma_events::event_kinds` have changed.
const EVENT_FIELDS: &[(&str, EventKindFn)] = &[
    ("origin_server_ts", is_non_stripped_room_event),
    ("room_id", |kind, var| {
        matches!(kind, EventKind::Message(_) | EventKind::State(_))
            && matches!(var, EventKindVariation::Full | EventKindVariation::Redacted)
    }),
    ("event_id", is_non_stripped_room_event),
    (
        "sender",
        |kind, _| matches!(kind, EventKind::Message(_) | EventKind::State(_) | EventKind::ToDevice(_)),
    ),
    ("state_key", |kind, _| matches!(kind, EventKind::State(_))),
    ("unsigned", is_non_stripped_room_event),
];

/// Create a content enum from `EventEnumInput`.
pub fn expand_event_enum(input: EventEnumInput) -> syn::Result<TokenStream> {
    let name = &input.name;
    let events = &input.events;
    let attrs = &input.attrs;
    let variants = events.iter().map(to_camel_case).collect::<syn::Result<Vec<_>>>()?;

    let event_enum =
        expand_any_with_deser(name, events, attrs, &variants, &EventKindVariation::Full);

    let sync_event_enum =
        expand_any_with_deser(name, events, attrs, &variants, &EventKindVariation::Sync);

    let event_stripped_enum =
        expand_any_with_deser(name, events, attrs, &variants, &EventKindVariation::Stripped);

    let redacted_event_enums = expand_any_redacted(name, events, attrs, &variants);

    let event_content_enum = expand_content_enum(name, events, attrs, &variants);

    Ok(quote! {
        #event_enum

        #sync_event_enum

        #event_stripped_enum

        #redacted_event_enums

        #event_content_enum
    })
}

fn expand_any_with_deser(
    kind: &EventKind,
    events: &[LitStr],
    attrs: &[Attribute],
    variants: &[Ident],
    var: &EventKindVariation,
) -> Option<TokenStream> {
    // If the event cannot be generated this bails out returning None which is rendered the same
    // as an empty `TokenStream`. This is effectively the check if the given input generates
    // a valid event enum.
    let (event_struct, ident) = generate_event_idents(kind, var)?;

    let content =
        events.iter().map(|event| to_event_path(event, &event_struct)).collect::<Vec<_>>();

    let (custom_variant, custom_deserialize) = generate_custom_variant(&event_struct, var);

    let any_enum = quote! {
        #( #attrs )*
        #[derive(Clone, Debug, ::serde::Serialize)]
        #[serde(untagged)]
        #[allow(clippy::large_enum_variant)]
        pub enum #ident {
            #(
                #[doc = #events]
                #variants(#content),
            )*
            #custom_variant
        }
    };

    let event_deserialize_impl = quote! {
        impl<'de> ::serde::de::Deserialize<'de> for #ident {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: ::serde::de::Deserializer<'de>,
            {
                use ::serde::de::Error as _;

                let json = Box::<::serde_json::value::RawValue>::deserialize(deserializer)?;
                let ::ruma_events::EventDeHelper { ev_type, .. } = ::ruma_events::from_raw_json_value(&json)?;
                match ev_type.as_str() {
                    #(
                        #events => {
                            let event = ::serde_json::from_str::<#content>(json.get()).map_err(D::Error::custom)?;
                            Ok(Self::#variants(event))
                        },
                    )*
                    #custom_deserialize
                }
            }
        }
    };

    let redacted_enum = expand_redacted_enum(kind, var);

    let field_accessor_impl = accessor_methods(kind, var, &variants);

    let redact_impl = expand_redact(&ident, kind, var, &variants);

    Some(quote! {
        #any_enum

        #field_accessor_impl

        #redact_impl

        #event_deserialize_impl

        #redacted_enum
    })
}

/// Generates the 3 redacted state enums, 2 redacted message enums,
/// and `Deserialize` implementations.
///
/// No content enums are generated since no part of the API deals with
/// redacted event's content. There are only five state variants that contain content.
fn expand_any_redacted(
    kind: &EventKind,
    events: &[LitStr],
    attrs: &[Attribute],
    variants: &[Ident],
) -> TokenStream {
    use EventKindVariation::*;

    if kind.is_state() {
        let full_state = expand_any_with_deser(kind, events, attrs, variants, &Redacted);
        let sync_state = expand_any_with_deser(kind, events, attrs, variants, &RedactedSync);
        let stripped_state =
            expand_any_with_deser(kind, events, attrs, variants, &RedactedStripped);

        quote! {
            #full_state

            #sync_state

            #stripped_state
        }
    } else if kind.is_message() {
        let full_message = expand_any_with_deser(kind, events, attrs, variants, &Redacted);
        let sync_message = expand_any_with_deser(kind, events, attrs, variants, &RedactedSync);

        quote! {
            #full_message

            #sync_message
        }
    } else {
        TokenStream::new()
    }
}

/// Create a content enum from `EventEnumInput`.
fn expand_content_enum(
    kind: &EventKind,
    events: &[LitStr],
    attrs: &[Attribute],
    variants: &[Ident],
) -> TokenStream {
    let ident = kind.to_content_enum();
    let event_type_str = events;

    let content = events.iter().map(to_event_content_path).collect::<Vec<_>>();

    let content_enum = quote! {
        #( #attrs )*
        #[derive(Clone, Debug, ::serde::Serialize)]
        #[serde(untagged)]
        #[allow(clippy::large_enum_variant)]
        pub enum #ident {
            #(
                #[doc = #event_type_str]
                #variants(#content),
            )*
            /// Content of an event not defined by the Matrix specification.
            Custom(::ruma_events::custom::CustomEventContent),
        }
    };

    let event_content_impl = quote! {
        impl ::ruma_events::EventContent for #ident {
            fn event_type(&self) -> &str {
                match self {
                    #( Self::#variants(content) => content.event_type(), )*
                    Self::Custom(content) => content.event_type(),
                }
            }

            fn from_parts(event_type: &str, input: Box<::serde_json::value::RawValue>) -> Result<Self, ::serde_json::Error> {
                match event_type {
                    #(
                        #event_type_str => {
                            let content = #content::from_parts(event_type, input)?;
                            Ok(Self::#variants(content))
                        },
                    )*
                    ev_type => {
                        let content = ::ruma_events::custom::CustomEventContent::from_parts(ev_type, input)?;
                        Ok(Self::Custom(content))
                    },
                }
            }
        }
    };

    let marker_trait_impls = marker_traits(&kind);

    quote! {
        #content_enum

        #event_content_impl

        #marker_trait_impls
    }
}

fn expand_redact(
    ident: &Ident,
    kind: &EventKind,
    var: &EventKindVariation,
    variants: &[Ident],
) -> Option<TokenStream> {
    if let EventKindVariation::Full | EventKindVariation::Sync | EventKindVariation::Stripped = var
    {
        let (param, redaction_type, redaction_enum) = match var {
            EventKindVariation::Full => {
                let struct_id = kind.to_event_ident(&EventKindVariation::Redacted)?;
                (
                    quote! { ::ruma_events::room::redaction::RedactionEvent },
                    quote! { ::ruma_events::#struct_id },
                    kind.to_event_enum_ident(&EventKindVariation::Redacted)?,
                )
            }
            EventKindVariation::Sync => {
                let struct_id = kind.to_event_ident(&EventKindVariation::RedactedSync)?;
                (
                    quote! { ::ruma_events::room::redaction::SyncRedactionEvent },
                    quote! { ::ruma_events::#struct_id },
                    kind.to_event_enum_ident(&EventKindVariation::RedactedSync)?,
                )
            }
            EventKindVariation::Stripped => {
                let struct_id = kind.to_event_ident(&EventKindVariation::RedactedStripped)?;
                (
                    quote! { ::ruma_events::room::redaction::SyncRedactionEvent },
                    quote! { ::ruma_events::#struct_id },
                    kind.to_event_enum_ident(&EventKindVariation::RedactedStripped)?,
                )
            }
            _ => return None,
        };

        let fields = EVENT_FIELDS
            .iter()
            .map(|(name, has_field)| generate_redacted_fields(name, kind, var, *has_field));

        let fields = quote! { #( #fields )* };

        Some(quote! {
            impl #ident {
                /// Redacts `Self` given a valid `Redaction[Sync]Event`.
                pub fn redact(self, redaction: #param, version: ::ruma_identifiers::RoomVersionId) -> #redaction_enum {
                    match self {
                        #(
                            Self::#variants(event) => {
                                let content = event.content.redact(version);
                                #redaction_enum::#variants(#redaction_type {
                                    content,
                                    #fields
                                })
                            }
                        )*
                        Self::Custom(event) => {
                            let content = event.content.redact(version);
                            #redaction_enum::Custom(#redaction_type {
                                content,
                                #fields
                            })
                        }
                    }
                }
            }
        })
    } else {
        None
    }
}

fn expand_redacted_enum(kind: &EventKind, var: &EventKindVariation) -> Option<TokenStream> {
    if let EventKind::State(_) | EventKind::Message(_) = kind {
        let ident = format_ident!("AnyPossiblyRedacted{}", kind.to_event_ident(var)?);

        let (regular_enum_ident, redacted_enum_ident) = inner_enum_idents(kind, var)?;
        Some(quote! {
            /// An enum that holds either regular un-redacted events or redacted events.
            #[derive(Clone, Debug, ::serde::Serialize)]
            #[serde(untagged)]
            pub enum #ident {
                /// An un-redacted event.
                Regular(#regular_enum_ident),
                /// A redacted event.
                Redacted(#redacted_enum_ident),
            }

            impl<'de> ::serde::de::Deserialize<'de> for #ident {
                fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
                where
                    D: ::serde::de::Deserializer<'de>,
                {
                    let json = Box::<::serde_json::value::RawValue>::deserialize(deserializer)?;
                    let ::ruma_events::EventDeHelper { unsigned, .. } = ::ruma_events::from_raw_json_value(&json)?;
                    Ok(match unsigned {
                        Some(unsigned) if unsigned.redacted_because.is_some() => {
                            Self::Redacted(::ruma_events::from_raw_json_value(&json)?)
                        }
                        _ => Self::Regular(::ruma_events::from_raw_json_value(&json)?),
                    })
                }
            }
        })
    } else {
        None
    }
}

fn generate_event_idents(kind: &EventKind, var: &EventKindVariation) -> Option<(Ident, Ident)> {
    Some((kind.to_event_ident(var)?, kind.to_event_enum_ident(var)?))
}

fn generate_redacted_fields(
    name: &str,
    kind: &EventKind,
    var: &EventKindVariation,
    is_event_kind: EventKindFn,
) -> TokenStream {
    if is_event_kind(kind, var) {
        let name = Ident::new(name, Span::call_site());

        if name == "unsigned" {
            let redaction_type = if let EventKindVariation::Sync = var {
                quote! { RedactedSyncUnsigned }
            } else {
                quote! { RedactedUnsigned }
            };

            quote! {
                unsigned: ::ruma_events::#redaction_type {
                    redacted_because: Some(::ruma_events::EventJson::from(redaction)),
                },
            }
        } else {
            quote! {
                #name: event.#name,
            }
        }
    } else {
        TokenStream::new()
    }
}

fn generate_custom_variant(
    event_struct: &Ident,
    var: &EventKindVariation,
) -> (TokenStream, TokenStream) {
    use EventKindVariation::*;

    if matches!(var, Redacted | RedactedSync | RedactedStripped) {
        (
            quote! {
                /// A redacted event not defined by the Matrix specification
                Custom(::ruma_events::#event_struct<::ruma_events::custom::RedactedCustomEventContent>),
            },
            quote! {
                event => {
                    let event = ::serde_json::from_str::<
                        ::ruma_events::#event_struct<::ruma_events::custom::RedactedCustomEventContent>,
                    >(json.get())
                    .map_err(D::Error::custom)?;

                    Ok(Self::Custom(event))
                },
            },
        )
    } else {
        (
            quote! {
                /// An event not defined by the Matrix specification
                Custom(::ruma_events::#event_struct<::ruma_events::custom::CustomEventContent>),
            },
            quote! {
                event => {
                    let event =
                        ::serde_json::from_str::<::ruma_events::#event_struct<::ruma_events::custom::CustomEventContent>>(json.get())
                            .map_err(D::Error::custom)?;

                    Ok(Self::Custom(event))
                },
            },
        )
    }
}

fn marker_traits(kind: &EventKind) -> TokenStream {
    let ident = kind.to_content_enum();
    match kind {
        EventKind::State(_) => quote! {
            impl ::ruma_events::RoomEventContent for #ident {}
            impl ::ruma_events::StateEventContent for #ident {}
        },
        EventKind::Message(_) => quote! {
            impl ::ruma_events::RoomEventContent for #ident {}
            impl ::ruma_events::MessageEventContent for #ident {}
        },
        EventKind::Ephemeral(_) => quote! {
            impl ::ruma_events::EphemeralRoomEventContent for #ident {}
        },
        EventKind::Basic(_) => quote! {
            impl ::ruma_events::BasicEventContent for #ident {}
        },
        _ => TokenStream::new(),
    }
}

fn accessor_methods(
    kind: &EventKind,
    var: &EventKindVariation,
    variants: &[Ident],
) -> Option<TokenStream> {
    use EventKindVariation::*;

    let ident = kind.to_event_enum_ident(var)?;

    // matching `EventKindVariation`s
    if let Redacted | RedactedSync | RedactedStripped = var {
        return redacted_accessor_methods(kind, var, variants);
    }

    let methods = EVENT_FIELDS
        .iter()
        .map(|(name, has_field)| generate_accessor(name, kind, var, *has_field, variants));

    let content_enum = kind.to_content_enum();

    let content = quote! {
        /// Returns the any content enum for this event.
        pub fn content(&self) -> #content_enum {
            match self {
                #(
                    Self::#variants(event) => #content_enum::#variants(event.content.clone()),
                )*
                Self::Custom(event) => #content_enum::Custom(event.content.clone()),
            }
        }
    };

    let prev_content = if has_prev_content_field(kind, var) {
        quote! {
            /// Returns the any content enum for this events prev_content.
            pub fn prev_content(&self) -> Option<#content_enum> {
                match self {
                    #(
                        Self::#variants(event) => {
                            event.prev_content.as_ref().map(|c| #content_enum::#variants(c.clone()))
                        },
                    )*
                    Self::Custom(event) => {
                        event.prev_content.as_ref().map(|c| #content_enum::Custom(c.clone()))
                    },
                }
            }
        }
    } else {
        TokenStream::new()
    };

    Some(quote! {
        impl #ident {
            #content

            #prev_content

            #( #methods )*
        }
    })
}

fn inner_enum_idents(kind: &EventKind, var: &EventKindVariation) -> Option<(Ident, Ident)> {
    match var {
        EventKindVariation::Full => Some((
            kind.to_event_enum_ident(var)?,
            kind.to_event_enum_ident(&EventKindVariation::Redacted)?,
        )),
        EventKindVariation::Sync => Some((
            kind.to_event_enum_ident(var)?,
            kind.to_event_enum_ident(&EventKindVariation::RedactedSync)?,
        )),
        EventKindVariation::Stripped => Some((
            kind.to_event_enum_ident(var)?,
            kind.to_event_enum_ident(&EventKindVariation::RedactedStripped)?,
        )),
        _ => None,
    }
}

/// Redacted events do NOT generate `content` or `prev_content` methods like
/// un-redacted events; otherwise, they are the same.
fn redacted_accessor_methods(
    kind: &EventKind,
    var: &EventKindVariation,
    variants: &[Ident],
) -> Option<TokenStream> {
    // this will never fail as it is called in `expand_any_with_deser`.
    let ident = kind.to_event_enum_ident(var).unwrap();
    let methods = EVENT_FIELDS
        .iter()
        .map(|(name, has_field)| generate_accessor(name, kind, var, *has_field, variants));

    Some(quote! {
        impl #ident {
            #( #methods )*
        }
    })
}

fn to_event_path(name: &LitStr, struct_name: &Ident) -> TokenStream {
    let span = name.span();
    let name = name.value();

    // There is no need to give a good compiler error as `to_camel_case` is called first.
    assert_eq!(&name[..2], "m.");

    let path = name[2..].split('.').collect::<Vec<_>>();

    let event_str = path.last().unwrap();
    let event = event_str
        .split('_')
        .map(|s| s.chars().next().unwrap().to_uppercase().to_string() + &s[1..])
        .collect::<String>();

    let path = path.iter().map(|s| Ident::new(s, span));

    match struct_name.to_string().as_str() {
        "MessageEvent" | "SyncMessageEvent" if name == "m.room.redaction" => {
            let redaction = if struct_name == "MessageEvent" {
                quote! { RedactionEvent }
            } else {
                quote! { SyncRedactionEvent }
            };
            quote! { ::ruma_events::room::redaction::#redaction }
        }
        "ToDeviceEvent" | "SyncStateEvent" | "StrippedStateEvent" | "SyncMessageEvent" => {
            let content = format_ident!("{}EventContent", event);
            quote! { ::ruma_events::#struct_name<::ruma_events::#( #path )::*::#content> }
        }
        struct_str if struct_str.contains("Redacted") => {
            let content = format_ident!("Redacted{}EventContent", event);
            quote! { ::ruma_events::#struct_name<::ruma_events::#( #path )::*::#content> }
        }
        _ => {
            let event_name = format_ident!("{}Event", event);
            quote! { ::ruma_events::#( #path )::*::#event_name }
        }
    }
}

fn to_event_content_path(name: &LitStr) -> TokenStream {
    let span = name.span();
    let name = name.value();

    // There is no need to give a good compiler error as `to_camel_case` is called first.
    assert_eq!(&name[..2], "m.");

    let path = name[2..].split('.').collect::<Vec<_>>();

    let event_str = path.last().unwrap();
    let event = event_str
        .split('_')
        .map(|s| s.chars().next().unwrap().to_uppercase().to_string() + &s[1..])
        .collect::<String>();

    let content_str = format_ident!("{}EventContent", event);
    let path = path.iter().map(|s| Ident::new(s, span));
    quote! {
        ::ruma_events::#( #path )::*::#content_str
    }
}

/// Splits the given `event_type` string on `.` and `_` removing the `m.room.` then
/// camel casing to give the `Event` struct name.
fn to_camel_case(name: &LitStr) -> syn::Result<Ident> {
    let span = name.span();
    let name = name.value();

    if &name[..2] != "m." {
        return Err(syn::Error::new(
            span,
            format!("well-known matrix events have to start with `m.` found `{}`", name),
        ));
    }

    let s = name[2..]
        .split(&['.', '_'] as &[char])
        .map(|s| s.chars().next().unwrap().to_uppercase().to_string() + &s[1..])
        .collect::<String>();

    Ok(Ident::new(&s, span))
}

fn generate_accessor(
    name: &str,
    kind: &EventKind,
    var: &EventKindVariation,
    is_event_kind: EventKindFn,
    variants: &[Ident],
) -> TokenStream {
    if is_event_kind(kind, var) {
        let field_type = field_return_type(name, var);

        let name = Ident::new(name, Span::call_site());
        let docs = format!("Returns this events {} field.", name);
        quote! {
            #[doc = #docs]
            pub fn #name(&self) -> &#field_type {
                match self {
                    #(
                        Self::#variants(event) => &event.#name,
                    )*
                    Self::Custom(event) => &event.#name,
                }
            }
        }
    } else {
        TokenStream::new()
    }
}

fn field_return_type(name: &str, var: &EventKindVariation) -> TokenStream {
    match name {
        "origin_server_ts" => quote! { ::std::time::SystemTime },
        "room_id" => quote! { ::ruma_identifiers::RoomId },
        "event_id" => quote! { ::ruma_identifiers::EventId },
        "sender" => quote! { ::ruma_identifiers::UserId },
        "state_key" => quote! { str },
        "unsigned" if &EventKindVariation::RedactedSync == var => {
            quote! { ::ruma_events::RedactedSyncUnsigned }
        }
        "unsigned" if &EventKindVariation::Redacted == var => {
            quote! { ::ruma_events::RedactedUnsigned }
        }
        "unsigned" => quote! { ::ruma_events::Unsigned },
        _ => panic!("the `ruma_events_macros::event_enum::EVENT_FIELD` const was changed"),
    }
}

/// Custom keywords for the `event_enum!` macro
mod kw {
    syn::custom_keyword!(kind);
    syn::custom_keyword!(events);
}

// If the variants of this enum change `to_event_path` needs to be updated as well.
#[derive(Eq, PartialEq)]
enum EventKindVariation {
    Full,
    Sync,
    Stripped,
    Redacted,
    RedactedSync,
    RedactedStripped,
}

// If the variants of this enum change `to_event_path` needs to be updated as well.
enum EventKind {
    Basic(Ident),
    Ephemeral(Ident),
    Message(Ident),
    State(Ident),
    ToDevice(Ident),
}

impl EventKind {
    fn is_state(&self) -> bool {
        matches!(self, Self::State(_))
    }

    fn is_message(&self) -> bool {
        matches!(self, Self::Message(_))
    }

    fn to_event_ident(&self, var: &EventKindVariation) -> Option<Ident> {
        use EventKindVariation::*;

        match (self, var) {
            // all `EventKind`s are valid event structs and event enums.
            (_, Full) => Some(format_ident!("{}Event", self.get_ident())),
            (Self::Ephemeral(i), Sync) | (Self::Message(i), Sync) | (Self::State(i), Sync) => {
                Some(format_ident!("Sync{}Event", i))
            }
            (Self::State(i), Stripped) => Some(format_ident!("Stripped{}Event", i)),
            (Self::Message(i), Redacted) | (Self::State(i), Redacted) => {
                Some(format_ident!("Redacted{}Event", i))
            }
            (Self::Message(i), RedactedSync) | (Self::State(i), RedactedSync) => {
                Some(format_ident!("RedactedSync{}Event", i))
            }
            (Self::State(i), RedactedStripped) => Some(format_ident!("RedactedStripped{}Event", i)),
            _ => None,
        }
    }

    fn to_event_enum_ident(&self, var: &EventKindVariation) -> Option<Ident> {
        Some(format_ident!("Any{}", self.to_event_ident(var)?))
    }

    /// `Any[kind]EventContent`
    fn to_content_enum(&self) -> Ident {
        format_ident!("Any{}EventContent", self.get_ident())
    }

    fn get_ident(&self) -> &Ident {
        match self {
            EventKind::Basic(i)
            | EventKind::Ephemeral(i)
            | EventKind::Message(i)
            | EventKind::State(i)
            | EventKind::ToDevice(i) => i,
        }
    }
}

impl Parse for EventKind {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let ident = input.parse::<Ident>()?;
        Ok(match ident.to_string().as_str() {
            "Basic" => EventKind::Basic(ident),
            "EphemeralRoom" => EventKind::Ephemeral(ident),
            "Message" => EventKind::Message(ident),
            "State" => EventKind::State(ident),
            "ToDevice" => EventKind::ToDevice(ident),
            id => {
                return Err(syn::Error::new(
                    input.span(),
                    format!(
                        "valid event kinds are Basic, EphemeralRoom, Message, State, ToDevice found `{}`",
                        id
                    ),
                ));
            }
        })
    }
}

/// The entire `event_enum!` macro structure directly as it appears in the source code.
pub struct EventEnumInput {
    /// Outer attributes on the field, such as a docstring.
    attrs: Vec<Attribute>,

    /// The name of the event.
    name: EventKind,

    /// An array of valid matrix event types. This will generate the variants of the event type "name".
    /// There needs to be a corresponding variant in `ruma_events::EventType` for
    /// this event (converted to a valid Rust-style type name by stripping `m.`, replacing the
    /// remaining dots by underscores and then converting from snake_case to CamelCase).
    events: Vec<LitStr>,
}

impl Parse for EventEnumInput {
    fn parse(input: ParseStream<'_>) -> parse::Result<Self> {
        let attrs = input.call(Attribute::parse_outer)?;
        // "name" field
        input.parse::<kw::kind>()?;
        input.parse::<Token![:]>()?;

        // the name of our event enum
        let name = input.parse::<EventKind>()?;
        input.parse::<Token![,]>()?;

        // "events" field
        input.parse::<kw::events>()?;
        input.parse::<Token![:]>()?;

        // an array of event names `["m.room.whatever", ...]`
        let ev_array = input.parse::<syn::ExprArray>()?;
        let events = ev_array
            .elems
            .into_iter()
            .map(|item| {
                if let Expr::Lit(ExprLit { lit: Lit::Str(lit_str), .. }) = item {
                    Ok(lit_str)
                } else {
                    let msg = "values of field `events` are required to be a string literal";
                    Err(syn::Error::new_spanned(item, msg))
                }
            })
            .collect::<syn::Result<_>>()?;

        Ok(Self { attrs, name, events })
    }
}