From 694ce4d66f2ba5e2a0435ea636bde7c5c5ba2f27 Mon Sep 17 00:00:00 2001
From: Michael Pfaff <michael@pfaff.dev>
Date: Sat, 28 May 2022 10:55:14 -0400
Subject: [PATCH] Overhaul

---
 src/lib.rs    | 126 +++++++--
 src/macros.rs | 702 +++++++++++++++++++++++++++-----------------------
 2 files changed, 483 insertions(+), 345 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 978ab6b..d7ad0a2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,9 +1,104 @@
-/// A dynamic query structure.
+//! A crate providing a (mostly) straighforward syntax for defining dynamic structures for
+//! efficient querying.
+//! 
+//! # Features
+//! 
+//! - Filter a struct or enum according to a query definition.
+//! - Inspect definitions manually to avoid unnecessary computations before filtering.
+//!
+//! # Attributes
+//!
+//! Attributes are fully supported on structs, struct fields, enums, enum variants, and enum
+//! variant fields. Additionally, attributes can be applied to some aspects of definitions, though
+//! this may be supported for all aspects in the future.
+//!
+//! # Structs
+//! 
+//! Only struct structs (yes, that is what they're [called](https://doc.rust-lang.org/reference/items/structs.html)),
+//! are supported. Struct structs with no fields are also not supported.
+//!
+//! This fails:
+//! ```compile_fail
+//! # #[macro_use] extern crate ql;
+//! #
+//! query_def! {
+//!     struct Foo {
+//!     }
+//! }
+//! #
+//! # fn main() {
+//! # }
+//! ```
+//!
+//! This works:
+//! ```
+//! # #[macro_use] extern crate ql;
+//! #
+//! query_def! {
+//!     struct Foo {
+//!         a: (bool),
+//!         b: (usize),
+//!         c: (String),
+//!         d: (Vec<String>),
+//!     }
+//! }
+//! #
+//! # fn main() {
+//! # }
+//! ```
+//!
+//! # Enums
+//! 
+//! Fieldless and struct enums are supported, but struct enums with no fields are not.
+//! 
+//! This fails:
+//! ```compile_fail
+//! # #[macro_use] extern crate ql;
+//! #
+//! query_def! {
+//!     enum Foo {
+//!         A { }
+//!     }
+//! }
+//! #
+//! # fn main() {
+//! # }
+//! ```
+//!
+//! This works:
+//! ```
+//! # #[macro_use] extern crate ql;
+//! #
+//! query_def! {
+//!     enum Foo {
+//!         A
+//!     }
+//! }
+//! #
+//! # fn main() {
+//! # }
+//! ```
+//!
+//! Incorrect syntax in the macro invocation can lead to very confusing errors.
+//!
+//! For example, the incorrect enum syntax shown earlier will fail with this message:
+//!
+//! ```text
+//! error: no rules expected the token `struct`
+//! ```
+
+
+/// A dynamic struct whose fields can be recursively filtered according to a
+/// [definition](`Self::Definition`).
 pub trait DynamicQuery {
+    /// A type defining the fields to include in the filtered structure.
     type Definition;
 
+    /// Filters the fields of this structure in place.
     fn filter_ref(&mut self, def: &Self::Definition);
 
+    /// Filters the fields of this structure in place. This method takes ownership of the
+    /// structure, making it more suitable for pipelines.
     #[inline(always)]
     fn filter(mut self, def: &Self::Definition) -> Self
     where
@@ -18,20 +113,20 @@ pub trait DynamicQuery {
 #[doc(hidden)]
 pub use paste;
 
+#[cfg(feature = "serde")]
+#[doc(hidden)]
+pub use serde;
+
 mod macros;
 
 #[cfg(test)]
 mod tests {
-    use serde::{Deserialize, Serialize};
-
     use super::DynamicQuery;
 
     // just tests that the macro compiles
-    crate::query_def_struct! {
-        /// Foo doc.
+    crate::query_def! {
         #[derive(PartialEq)]
-        Foo {
-            /// Field doc.
+        struct Foo {
             #[serde(flatten)]
             bar: (Bar),
             baz: (bool),
@@ -39,15 +134,12 @@ mod tests {
             bars_by_bazs: 'map (bool, Bar),
         }
 
-        /// Bar doc.
         #[derive(PartialEq)]
-        Bar {
+        struct Bar {
             baz_inner: (bool),
         }
-    }
 
-    crate::query_def_enum! {
-        FooOrBar {
+        enum FooOrBar {
             Foo {
                 value: 'dyn (Foo),
             },
@@ -57,22 +149,20 @@ mod tests {
             }
         }
 
-        OptionalFooOrBarDyn {
+        enum OptionalFooOrBarDyn {
             Some {
                 value: 'dyn (FooOrBar),
             },
 
-            None {
-            }
+            None,
         }
 
-        OptionalFooOrBar {
+        enum OptionalFooOrBar {
             Some {
                 value: (FooOrBar),
             },
 
-            None {
-            }
+            None
         }
     }
 
diff --git a/src/macros.rs b/src/macros.rs
index 54261e8..375f994 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -1,16 +1,16 @@
 #[doc(hidden)]
 #[macro_export]
 macro_rules! query_def_type {
-    (@ ($type:ty)) => {
+    (($type:ty)) => {
         $type
     };
-    (@ 'dyn ($type:ty)) => {
+    ('dyn ($type:ty)) => {
         $type
     };
-    (@ 'vec ($type:ty)) => {
+    ('vec ($type:ty)) => {
         ::std::vec::Vec<$type>
     };
-    (@ 'map ($key:ty, $value:ty)) => {
+    ('map ($key:ty, $value:ty)) => {
         ::std::collections::HashMap<$key, $value>
     };
 }
@@ -21,16 +21,16 @@ macro_rules! query_def_field {
     (@dyn $type:ty) => {
         Option<<$type as $crate::DynamicQuery>::Definition>
     };
-    (@ ($type:ty)) => {
+    (($type:ty)) => {
         bool
     };
-    (@ 'dyn ($type:ty)) => {
+    ('dyn ($type:ty)) => {
         $crate::query_def_field!(@dyn $type)
     };
-    (@ 'vec ($type:ty)) => {
+    ('vec ($type:ty)) => {
         $crate::query_def_field!(@dyn $type)
     };
-    (@ 'map ($key:ty, $value:ty)) => {
+    ('map ($key:ty, $value:ty)) => {
         $crate::query_def_field!(@dyn $value)
     };
 }
@@ -39,8 +39,9 @@ macro_rules! query_def_field {
 #[macro_export]
 macro_rules! query_def_filter {
     // note about this: 'dyn is implied for 'vec and 'map because if the type is not 'dyn, then the
-    // special handling is not necessary in the first place.
-    (@ $query:expr, $value:ident, 'vec ($_type:path)) => {
+    // special handling is not necessary in the first place (i.e. you can just do `(Vec<Type>)`
+    // instead of `'vec (Type)`.
+    ($query:expr, $value:ident, 'vec ($_type:path)) => {
         match $query {
             Some(query) => {
                 if let Some(ref mut value) = $value {
@@ -54,7 +55,7 @@ macro_rules! query_def_filter {
             }
         }
     };
-    (@ $query:expr, $value:ident, 'map ($_key:path, $_value:path)) => {
+    ($query:expr, $value:ident, 'map ($_key:path, $_value:path)) => {
         match $query {
             Some(query) => {
                 if let Some(ref mut value) = $value {
@@ -68,14 +69,14 @@ macro_rules! query_def_filter {
             }
         }
     };
-    (@ $query:expr, $value:ident, 'dyn ($($_type:tt)+)) => {
+    ($query:expr, $value:ident, 'dyn ($($_type:tt)+)) => {
         if let Some(ref mut value) = $value {
             if let Some(ref query) = $query {
                 value.filter_ref(&query);
             }
         }
     };
-    (@ $query:expr, $value:ident, ($($_type:tt)+)) => {
+    ($query:expr, $value:ident, ($($_type:tt)+)) => {
         if !*$query {
             *$value = None;
         }
@@ -85,368 +86,415 @@ macro_rules! query_def_filter {
 #[doc(hidden)]
 #[macro_export]
 macro_rules! query_def_internal_struct {
-    (@
-        $(
-            $(#[$meta:meta])
-            *
-            $vis:vis $data:ident$((
-                $(#[$def_meta:meta])
-                +
-            ))? {
-                $(
-                    $(#[$field_meta:meta])
-                    *
-                    $field:ident: $($qualifier:lifetime)? ($($type:tt)+),
-                )+
-            }
-        )
-        *
+    (
+        $( #[$meta:meta] )*
+        $vis:vis $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $(
+                $( #[$field_meta:meta] )*
+                $field:ident: $( $qualifier:lifetime )? ($( $type:tt )+)
+            ),+
+
+            $(,)?
+        }
     ) => {
-        $(
-            #[derive(Debug, Clone)]
-            $(#[$meta])
-            *
-            $vis struct $data {
+        #[derive(Debug, Clone)]
+        $( #[$meta] )*
+        $vis struct $data {
+            $(
+                $( #[$field_meta] )*
+                pub $field: Option<$crate::query_def_type!($( $qualifier )? ($( $type )+))>
+            ),+
+        }
+
+        $crate::paste::paste! {
+            #[derive(Debug, Clone, Copy, Default)]
+            $( $( #[$def_meta] )+ )?
+            $vis struct [<$data Def>] {
+                $( pub $field: $crate::query_def_field!($( $qualifier )? ($( $type )+)) ),+
+            }
+        }
+
+        impl $crate::DynamicQuery for $data {
+            type Definition = $crate::paste::paste! { [<$data Def>] };
+
+            fn filter_ref(&mut self, def: &Self::Definition) {
                 $(
-                    $(#[$field_meta])
-                    *
-                    pub $field: Option<$crate::query_def_type!(@ $($qualifier)? ($($type)+))>,
+                    let query = &def.$field;
+                    let value = &mut self.$field;
+                    $crate::query_def_filter!(query, value, $( $qualifier )? ($( $type )+));
                 )+
             }
+        }
+    };
+}
 
-            $crate::paste::paste! {
-                #[derive(Debug, Clone, Copy, Default)]
-                $( $( #[$def_meta] )+ )?
-                $vis struct [<$data Def>] {
-                    $(
-                        pub $field: $crate::query_def_field!(@ $($qualifier)? ($($type)+)),
-                    )+
-                }
-            }
-
-            impl $crate::DynamicQuery for $data {
-                type Definition = $crate::paste::paste! { [<$data Def>] };
-
-                fn filter_ref(&mut self, def: &Self::Definition) {
-                    $(
-                        let query = &def.$field;
-                        let value = &mut self.$field;
-                        $crate::query_def_filter!(@ query, value, $($qualifier)? ($($type)+));
-                    )
-                    +
-                }
-            }
-        )
-        *
+#[doc(hidden)]
+#[macro_export]
+macro_rules! query_def_internal_enum_variant_def {
+    (
+        $( #[$variant_def_meta:meta] )*
+        $vis:vis $name:ident
+    ) => {
+        #[derive(Debug, Clone, Copy, Default)]
+        $( #[$variant_def_meta] )*
+        $vis struct $name;
+    };
+    (
+        $( #[$variant_def_meta:meta] )*
+        $vis:vis $name:ident {
+            $( $field:ident$((
+                $( #[$variant_def_field_meta:meta] )+
+            ))?: $($qualifier:lifetime)? ($($type:tt)+) ),+
+        }
+    ) => {
+        #[derive(Debug, Clone, Copy, Default)]
+        $( #[$variant_def_meta] )*
+        $vis struct $name {
+            $(
+                $( $( #[$variant_def_field_meta] )+ )?
+                pub $field: $crate::query_def_field!($( $qualifier )? ($( $type )+))
+            ),+
+        }
     };
 }
 
 #[doc(hidden)]
 #[macro_export]
 macro_rules! query_def_internal_enum {
-    (@
-        $(
-            $(#[$meta:meta])
-            *
-            $vis:vis $data:ident$((
-                $(#[$def_meta:meta])
-                +
-            ))? {
-                $(
-                    $( #[$variant_meta:meta] )*
-                    $variant:ident$((
-                        $(#[$variant_def_meta:meta])
-                        +
-                    ))? {
-                        $(
-                            $(#[$field_meta:meta])
-                            *
-                            $field:ident: $($qualifier:lifetime)? ($($type:tt)+),
-                        )*
-                    }
-                ),+
-            }
-        )
-        *
-    ) => {
-        $(
-            #[derive(Debug, Clone)]
-            $(#[$meta])
-            *
-            $vis enum $data {
-                $(
-                    $( #[$variant_meta] )*
-                    $variant {
-                        $(
-                            $(#[$field_meta])
-                            *
-                            $field: Option<$crate::query_def_type!(@ $($qualifier)? ($($type)+))>,
-                        )*
-                    }
-                ),+
-            }
-
-            $crate::paste::paste! {
-                #[derive(Debug, Clone, Copy, Default)]
-                $( $( #[$def_meta] )+ )?
-                $vis struct [<$data Def>] {
+    (
+        $( #[$meta:meta] )*
+        $vis:vis $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $(
+                $( #[$variant_meta:meta] )*
+                $variant:ident$((
+                    $( #[$variant_def_meta:meta] )+
+                ))? $({
                     $(
-                        pub [<$variant:snake:lower>]: [<$data Def Variant $variant>],
+                        $( #[$field_meta:meta] )*
+                        $field:ident$((
+                            $( #[$variant_def_field_meta:meta] )+
+                        ))?: $( $qualifier:lifetime )? ($( $type:tt )+)
+                    ),+
+                    $(,)?
+                })?
+            ),+
+
+            $(,)?
+        }
+    ) => {
+        #[derive(Debug, Clone)]
+        $( #[$meta] )*
+        $vis enum $data {
+            $(
+                $( #[$variant_meta] )*
+                $variant $({
+                    $(
+                        $( #[$field_meta] )*
+                        $field: Option<$crate::query_def_type!($( $qualifier )? ($( $type )+))>
+                    ),*
+                })?
+            ),+
+        }
+
+        $crate::paste::paste! {
+            #[derive(Debug, Clone, Copy, Default)]
+            $( $( #[$def_meta] )+ )?
+            $vis struct [<$data Def>] {
+                $( pub [<$variant:snake:lower>]: [<$data Def Variant $variant>] ),+
+            }
+        }
+
+//        $crate::paste::paste! {
+//            impl [<$data Def>] {
+//                $(
+//                    pub type $variant = [<$data Def Variant $variant>];
+//                )+
+//            }
+//        }
+
+        $crate::paste::paste! {
+            $(
+                $crate::query_def_internal_enum_variant_def! {
+                    $( $( #[$variant_def_meta] )+ )?
+                    $vis [<$data Def Variant $variant>] $({
+                        $( $field$((
+                            $( #[$variant_def_field_meta] )+
+                        ))?: $( $qualifier )? ($( $type )+) ),+
+                    })?
+                }
+            )+
+        }
+
+        impl $crate::DynamicQuery for $data {
+            type Definition = $crate::paste::paste! { [<$data Def>] };
+
+            fn filter_ref(&mut self, def: &Self::Definition) {
+                match self {
+                    $(
+                        Self::$variant $({ $( ref mut $field ),* })? => {
+                            $($(
+                                let query = &$crate::paste::paste! { &def.[<$variant:snake:lower>] }.$field;
+                                $crate::query_def_filter!(query, $field, $( $qualifier )? ($( $type )+));
+                            )*)?
+                        }
                     )+
                 }
             }
-
-            $crate::paste::paste! {
-//                impl [<$data Def>] {
-//                    $(
-//                        pub type $variant = [<$data Def Variant $variant>];
-//                    )+
-//                }
-
-                $(
-                    #[derive(Debug, Clone, Copy, Default)]
-                    $( $( #[$variant_def_meta] )+ )?
-                    $vis struct [<$data Def Variant $variant>] {
-                        $(
-                            pub $field: $crate::query_def_field!(@ $($qualifier)? ($($type)+)),
-                        )*
-                    }
-                )+
-            }
-
-            impl $crate::DynamicQuery for $data {
-                type Definition = $crate::paste::paste! { [<$data Def>] };
-
-                fn filter_ref(&mut self, def: &Self::Definition) {
-                    match self {
-                        $(
-                            Self::$variant { $( ref mut $field ),* } => {
-                                $(
-                                    let query = &$crate::paste::paste! { &def.[<$variant:snake:lower>] }.$field;
-                                    $crate::query_def_filter!(@ query, $field, $($qualifier)? ($($type)+));
-                                )*
-                            }
-                        )+
-                    }
-                }
-            }
-        )
-        *
+        }
     };
 }
 
-/// Defines a dynamic query structure.
 #[cfg(not(feature = "serde"))]
+#[doc(hidden)]
 #[macro_export]
-macro_rules! query_def_struct {
+macro_rules! query_def_0 {
     (
-        $(
-            $(#[$meta:meta])
-            *
-            $vis:vis $data:ident$((
-                $(#[$def_meta:meta])
-                +
-            ))? {
-                $(
-                    $(#[$field_meta:meta])
-                    *
-                    $field:ident: $($qualifier:lifetime)? ($($type:tt)+),
-                )+
-            }
-        )
-        *
-    ) => {
-        $crate::query_def_internal_struct!(@
-        $(
-            $(#[$meta])
-            *
-            $vis $data$((
-                $(#[$def_meta])
-                +
-            ))? {
-                $(
-                    $(#[$field_meta])
-                    *
-                    $field: $($qualifier)? ($($type)+),
-                )+
-            }
-        )
-        *
-        );
-    };
-}
+        $( #[$meta:meta] )*
+        $vis:vis struct $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $(
+                $( #[$field_meta:meta] )*
+                $field:ident: $( $qualifier:lifetime )? ($( $type:tt )+)
+            ),+
 
-/// Defines a dynamic enumerated query structure.
-#[cfg(not(feature = "serde"))]
-#[macro_export]
-macro_rules! query_def_enum {
-    (
-        $(
-            $(#[$meta:meta])
-            *
-            $vis:vis $data:ident$((
-                $(#[$def_meta:meta])
-                +
-            ))? {
-                $(
-                    $(#[$variant_meta:meta])
-                    *
-                    $variant:ident$((
-                        $(#[$variant_def_meta:meta])
-                        +
-                    ))? {
-                        $(
-                            $(#[$field_meta:meta])
-                            *
-                            $field:ident: $($qualifier:lifetime)? ($($type:tt)+),
-                        )*
-                    }
-                ),+
-            }
-        )
-        *
+            $(,)?
+        }
     ) => {
-        $crate::query_def_internal_enum!(@
-        $(
-            $(#[$meta])
-            *
+        $crate::query_def_internal_struct! {
+            $( #[$meta] )*
             $vis $data$((
-                $(#[$def_meta])
-                +
+                $( #[$def_meta] )+
             ))? {
                 $(
-                    $(#[$variant_meta])
-                    *
+                    $( #[$field_meta] )*
+                    $field: $( $qualifier )? ($( $type )+),
+                )+
+            }
+        }
+    };
+    (
+        $( #[$meta:meta] )*
+        $vis:vis enum $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $(
+                $( #[$variant_meta:meta] )*
+                $variant:ident$((
+                    $( #[$variant_def_meta:meta] )+
+                ))? $({
+                    $(
+                        $( #[$field_meta:meta] )*
+                        $field:ident: $( $qualifier:lifetime )? ($( $type:tt )+)
+                    ),+
+
+                    $(,)?
+                })?
+            ),+
+
+            $(,)?
+        }
+    ) => {
+        $crate::query_def_internal_enum! {
+            $( #[$meta] )*
+            $vis $data$((
+                $( #[$def_meta] )+
+            ))? {
+                $(
+                    $( #[$variant_meta] )*
                     $variant$((
-                        $(#[$variant_def_meta])
-                        ?
-                    ))? {
+                        $( #[$variant_def_meta] )?
+                    ))? $({
                         $(
-                            $(#[$field_meta])
-                            *
-                            $field: $($qualifier)? ($($type)+),
-                        )*
-                    }
+                            $( #[$field_meta] )*
+                            $field: $( $qualifier )? ($( $type )+)
+                        ),+
+                    })?
                 ),+
             }
-        )
-        *
-        );
+        }
     };
 }
 
-/// Defines a dynamic query structure.
 #[cfg(feature = "serde")]
+#[doc(hidden)]
 #[macro_export]
-macro_rules! query_def_struct {
+macro_rules! query_def_0 {
     (
-        $(
-            $(#[$meta:meta])
-            *
-            $vis:vis $data:ident$((
-                $(#[$def_meta:meta])
-                +
-            ))? {
-                $(
-                    $(#[$field_meta:meta])
-                    *
-                    $field:ident: $($qualifier:lifetime)? ($($type:tt)+),
-                )+
-            }
-        )
-        *
+        $( #[$meta:meta] )*
+        $vis:vis struct $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $(
+                $( #[$field_meta:meta] )*
+                $field:ident: $( $qualifier:lifetime )? ($( $type:tt )+)
+            ),+
+
+            $(,)?
+        }
     ) => {
-        $crate::query_def_internal_struct!(@
-        $(
-            #[derive(Serialize, Deserialize)]
-            $(#[$meta])
-            *
+        $crate::query_def_internal_struct! {
+            #[derive($crate::serde::Serialize, $crate::serde::Deserialize)]
+            $( #[$meta] )*
             $vis $data(
-                #[derive(Serialize, Deserialize)]
+                #[derive($crate::serde::Serialize, $crate::serde::Deserialize)]
                 #[serde(default)]
-                $(
-                $(#[$def_meta])
-                +
-                )?
+                $( $( #[$def_meta] )+ )?
             ) {
                 $(
                     #[serde(skip_serializing_if = "Option::is_none")]
-                    $(#[$field_meta])
-                    *
-                    $field: $($qualifier)? ($($type)+),
-                )+
+                    $( #[$field_meta] )*
+                    $field: $( $qualifier )? ($( $type )+)
+                ),+
             }
-        )
-        *
-        );
+        }
+    };
+    (
+        $( #[$meta:meta] )*
+        $vis:vis enum $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $(
+                $( #[$variant_meta:meta] )*
+                $variant:ident$((
+                    $( #[$variant_def_meta:meta] )+
+                ))? $({
+                    $(
+                        $( #[$field_meta:meta] )*
+                        $field:ident: $( $qualifier:lifetime )? ($( $type:tt )+)
+                    ),+
+
+                    $(,)?
+                })?
+            ),+
+
+            $(,)?
+        }
+    ) => {
+        $crate::query_def_internal_enum! {
+            #[derive($crate::serde::Serialize, $crate::serde::Deserialize)]
+            $( #[$meta] )*
+            $vis $data(
+                #[derive($crate::serde::Serialize, $crate::serde::Deserialize)]
+                #[serde(default)]
+                $( $( #[$def_meta] )+ )?
+            ) {
+                $(
+                    $( #[$variant_meta] )*
+                    $variant(
+                        #[derive($crate::serde::Serialize, $crate::serde::Deserialize)]
+                        $( $( #[$variant_def_meta] )+ )?
+                    ) $({
+                        $(
+                            #[serde(skip_serializing_if = "Option::is_none")]
+                            $( #[$field_meta] )*
+                            $field(
+                                #[serde(default)]
+                            ): $( $qualifier )? ($( $type )+),
+                        )+
+                    })?
+                ),+
+            }
+        }
     };
 }
 
-/// Defines a dynamic enumerated query structure.
-#[cfg(feature = "serde")]
+/// Defines a dynamic query structure.
+///
+/// # Structs
+/// 
+/// Only struct structs (yes, that is what they're [called](https://doc.rust-lang.org/reference/items/structs.html)), are supported. Struct structs with no fields are also not supported.
+///
+/// This fails:
+/// ```compile_fail
+/// # #[macro_use] extern crate ql;
+/// #
+/// query_def! {
+///     struct Foo {
+///     }
+/// }
+/// #
+/// # fn main() {
+/// # }
+/// ```
+///
+/// This works:
+/// ```
+/// # #[macro_use] extern crate ql;
+/// #
+/// query_def! {
+///     struct Foo {
+///         a: (bool),
+///         b: (usize),
+///         c: (String),
+///         d: (Vec<String>),
+///     }
+/// }
+/// #
+/// # fn main() {
+/// # }
+/// ```
+///
+/// # Enums
+/// 
+/// Fieldless and struct enums are supported, but struct enums with no fields are not.
+/// 
+/// This fails:
+/// ```compile_fail
+/// # #[macro_use] extern crate ql;
+/// #
+/// query_def! {
+///     enum Foo {
+///         A { }
+///     }
+/// }
+/// #
+/// # fn main() {
+/// # }
+/// ```
+///
+/// This works:
+/// ```
+/// # #[macro_use] extern crate ql;
+/// #
+/// query_def! {
+///     enum Foo {
+///         A
+///     }
+/// }
+/// #
+/// # fn main() {
+/// # }
+/// ```
+///
+/// Incorrect syntax in the macro invocation can lead to very confusing errors.
+///
+/// For example, the incorrect enum syntax shown earlier will fail with this message:
+///
+/// ```text
+/// error: no rules expected the token `struct`
+/// ```
 #[macro_export]
-macro_rules! query_def_enum {
-    (
-        $(
-            $(#[$meta:meta])
-            *
-            $vis:vis $data:ident$((
-                $(#[$def_meta:meta])
-                +
+macro_rules! query_def {
+    ($(
+        $( #[$meta:meta] )*
+        $vis:vis $type:ident $data:ident$((
+            $( #[$def_meta:meta] )+
+        ))? {
+            $($body:tt)+
+        }
+    )*) => {
+        $($crate::query_def_0! {
+            $( #[$meta] )*
+            $vis $type $data$((
+                $( #[$def_meta] )+
             ))? {
-                $(
-                    $(#[$variant_meta:meta])
-                    *
-                    $variant:ident$((
-                        $(#[$variant_def_meta:meta])
-                        +
-                    ))? {
-                        $(
-                            $(#[$field_meta:meta])
-                            *
-                            $field:ident: $($qualifier:lifetime)? ($($type:tt)+),
-                        )*
-                    }
-                ),+
+                $($body)+
             }
-        )
-        *
-    ) => {
-        $crate::query_def_internal_enum!(@
-        $(
-            #[derive(Serialize, Deserialize)]
-            $(#[$meta])
-            *
-            $vis $data(
-                #[derive(Serialize, Deserialize)]
-                #[serde(default)]
-                $(
-                $(#[$def_meta])
-                +
-                )?
-            ) {
-                $(
-                    $(#[$variant_meta])
-                    *
-                    $variant(
-                        #[derive(Serialize, Deserialize)]
-                        #[serde(default)]
-                        $(
-                        $(#[$variant_def_meta])
-                        +
-                        )?
-                    ) {
-                        $(
-                            #[serde(skip_serializing_if = "Option::is_none")]
-                            $(#[$field_meta])
-                            *
-                            $field: $($qualifier)? ($($type)+),
-                        )*
-                    }
-                ),+
-            }
-        )
-        *
-        );
+        })*
     };
 }