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/// Statically check presence of field in a given struct and stringify it.
///
/// Note that it sadly won't work with `#[serde(rename = "...")]` and `#[serde(rename_all = "...")]`.
///
/// # Example
///
/// ```
/// use mongodm::mongo::bson::doc;
/// use mongodm::field;
/// use mongodm::operator::*;
///
/// struct MyModel {
///     foo: i64,
///     bar: i64,
///     lorem: String,
/// }
///
/// // Statically checked
/// let a = doc! {
///     And: [
///         { field!(foo in MyModel): { Exists: true } },
///         {
///             Or: [
///                 { field!(bar in MyModel): { GreaterThan: 100 } },
///                 { field!(lorem in MyModel): "ipsum" }
///             ]
///         },
///         // dollar and double dollar signs can inserted by prefixing with @
///         { field!(@foo in MyModel): field!(@@bar in MyModel) }
///     ]
/// };
///
/// // Hardcoded strings
/// let b = doc! {
///     "$and": [
///         { "foo": { "$exists": true } },
///         {
///             "$or": [
///                 { "bar": { "$gt": 100 } },
///                 { "lorem": "ipsum" }
///             ]
///         },
///         { "$foo": "$$bar" }
///     ]
/// };
///
/// // Generated document are identicals
/// assert_eq!(a, b);
/// ```
///
/// Nested structs
/// ```
/// use mongodm::mongo::bson::doc;
/// use mongodm::field;
///
/// struct Foo {
///     bar: Bar,
/// }
///
/// struct Bar {
///     lorem: String,
///     baz: Baz,
/// }
///
/// struct Baz {
///     dolor: String,
/// }
///
/// assert_eq!(
///     doc! { field!((bar in Foo).(lorem in Bar)): "ipsum" },
///     doc! { "bar.lorem": "ipsum" },
/// );
///
/// assert_eq!(
///     doc! { field!(@@(bar in Foo).(baz in Bar).(dolor in Baz)): "sit amet" },
///     doc! { "$$bar.baz.dolor": "sit amet" },
/// );
/// ```
///
/// If the field doesn't exist, compilation will fail.
///
/// ```compile_fail
/// use mongodm::mongo::bson::doc;
/// use mongodm::field;
///
/// struct MyModel {
///     foo: i64,
///     bar: Bar,
/// }
///
/// struct Bar {
///     baz: i64,
/// }
///
/// // Doesn't compile because `baz` isn't a member of `MyModel`
/// doc! { field!(baz in MyModel): 0 };
///
/// // Doesn't compile because `foo` isn't a member of `Bar`
/// doc! { field!((bar in MyModel).(foo in Bar)): 0 };
/// ```
#[macro_export]
macro_rules! field {
    ( $field:ident in $type:path ) => {{
        #[allow(unknown_lints, unneeded_field_pattern)]
        const _: fn() = || {
            let $type { $field: _, .. };
        };
        stringify!( $field )
    }};
    ( @ $field:ident in $type:path ) => {{
        #[allow(unknown_lints, unneeded_field_pattern)]
        const _: fn() = || {
            let $type { $field: _, .. };
        };
        concat!("$", stringify!($field))
    }};
    ( @ @ $field:ident in $type:path ) => {{
        #[allow(unknown_lints, unneeded_field_pattern)]
        const _: fn() = || {
            let $type { $field: _, .. };
        };
        concat!("$$", stringify!($field))
    }};
    ( ( $field:ident in $type:path ) )  => {{
        $crate::field!( $field in $type )
    }};
    // FIXME: ideally we want a compile-time string instead of format!
    ( ( $field:ident in $type:path ) . $( $rest:tt ).+ ) => {{
        format!("{}.{}", $crate::field!( $field in $type ), $crate::field!( $( $rest ).+ ))
    }};
    ( @ ( $field:ident in $type:path ) . $( $rest:tt ).+ ) => {{
        format!("${}.{}", $crate::field!( $field in $type ), $crate::field!( $( $rest ).+ ))
    }};
    ( @ @ ( $field:ident in $type:path ) . $( $rest:tt ).+ ) => {{
        format!("$${}.{}", $crate::field!( $field in $type ), $crate::field!( $( $rest ).+ ))
    }};
}

/// Shorthand for `field!`.
///
/// # Example
///
/// ```
/// use mongodm::mongo::bson::doc;
/// use mongodm::f;
/// use mongodm::operator::*;
///
/// struct MyModel {
///     foo: i64,
///     bar: i64,
///     lorem: String,
/// }
///
/// // Statically checked
/// let a = doc! {
///     And: [
///         { f!(foo in MyModel): { Exists: true } },
///         {
///             Or: [
///                 { f!(bar in MyModel): { GreaterThan: 100 } },
///                 { f!(lorem in MyModel): "ipsum" }
///             ]
///         },
///         // dollar and double dollar signs can inserted by prefixing with @
///         { f!(@foo in MyModel): f!(@@bar in MyModel) }
///     ]
/// };
///
/// // Hardcoded strings
/// let b = doc! {
///     "$and": [
///         { "foo": { "$exists": true } },
///         {
///             "$or": [
///                 { "bar": { "$gt": 100 } },
///                 { "lorem": "ipsum" }
///             ]
///         },
///         { "$foo": "$$bar" }
///     ]
/// };
///
/// // Generated document are identicals
/// assert_eq!(a, b);
/// ```
#[macro_export]
macro_rules! f {
    ( $field:ident in $type:path ) => {{
        $crate::field!($field in $type)
    }};
    ( @ $field:ident in $type:path ) => {{
        $crate::field!( @ $field in $type)
    }};
    ( @ @ $field:ident in $type:path ) => {{
        $crate::field!( @ @ $field in $type)
    }};
    ( ( $field:ident in $type:path ) )  => {{
        $crate::field!( ( $field in $type ) )
    }};
    ( ( $field:ident in $type:path ) . $( $rest:tt ).+ ) => {{
        $crate::field!( ( $field in $type ) . $( $rest ).+ )
    }};
    ( @ ( $field:ident in $type:path ) . $( $rest:tt ).+ ) => {{
        $crate::field!( @ ( $field in $type ) . $( $rest ).+ )
    }};
    ( @ @ ( $field:ident in $type:path ) . $( $rest:tt ).+ ) => {{
        $crate::field!( @ @ ( $field in $type ) . $( $rest ).+ )
    }};
}