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    //! This module provides two utility macros for testing custom derives. They can
    //! be used together to eliminate some of the boilerplate required in order to
    //! declare and test custom derive implementations.

    // XXX: Stop using `ignore` blocks for examples in this module.

    // Re-exports used by the decl_derive! and test_derive!
    pub mod syn {
        pub use syn::*; // For syn::parse_derive_input
    }

    pub mod quote {
        pub use quote::*; // For quote::Tokens
    }

    pub mod proc_macro {
        pub use proc_macro::*; // For proc_macro::TokenStream
    }

    /// The `decl_derive!` macro declares a custom derive wrapper. It will parse the
    /// incoming TokenStream into a `synstructure::Structure` object, and pass it
    /// into the inner function.
    ///
    /// Your inner function should have the following type:
    ///
    /// ```
    /// # extern crate quote;
    /// # extern crate synstructure;
    /// fn derive(input: synstructure::Structure) -> quote::Tokens {
    ///     // Your body here
    /// # unimplemented!()
    /// }
    /// ```
    ///
    /// # Usage
    ///
    /// ```ignore
    /// fn derive_interesting(mut input: synstructure::Structure) -> quote::Tokens {
    ///     // Your body here
    /// }
    /// decl_derive!([Interesting, attributes(interesting_ignore)] => derive_interesting);
    /// ```
    #[macro_export]
    macro_rules! decl_derive {
        // XXX: Switch to using this variant everywhere?
        ([$derives:ident $($derive_t:tt)*] => $inner:path) => {
            #[proc_macro_derive($derives $($derive_t)*)]
            #[allow(non_snake_case)]
            pub fn $derives(
                i: $crate::macros::proc_macro::TokenStream
            ) -> $crate::macros::proc_macro::TokenStream
            {
                let parsed = $crate::macros::syn::parse_derive_input(&i.to_string())
                    .expect(concat!("Failed to parse input to `#[derive(",
                                    stringify!($derives),
                                    ")]`"));
                $inner($crate::Structure::new(&parsed)).parse()
                    .expect(concat!("Failed to parse output from `#[derive(",
                                    stringify!($derives),
                                    ")]`"))
            }
        };
    }

    /// Run a test on a custom derive. This macro expands both the original struct
    /// and the expansion to ensure that they compile correctly, and confirms that
    /// feeding the original struct into the named derive will produce the written
    /// output.
    ///
    /// You can add `no_build` to the end of the macro invocation to disable
    /// checking that the written code compiles. This is useful in contexts where
    /// the procedural macro cannot depend on the crate where it is used during
    /// tests.
    ///
    /// # Usage
    ///
    /// ```ignore
    /// test_derive!{
    ///     super::derive_interesting {
    ///         struct A {
    ///             a: i32,
    ///             b: i32,
    ///         }
    ///     }
    ///     expands to {
    ///         impl ::Interesting for A {
    ///             fn is_interesting(&self) -> bool {
    ///                 match *self {
    ///                     A { a: ref __binding_0, b: ref __binding_1, } => {
    ///                         false ||
    ///                             ::Interesting::is_interesting(__binding_0) ||
    ///                             ::Interesting::is_interesting(__binding_1)
    ///                     }
    ///                 }
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    #[macro_export]
    macro_rules! test_derive {
        ($name:path { $($i:tt)* } expands to { $($o:tt)* }) => {
            {
                #[allow(dead_code)]
                fn ensure_compiles() {
                    $($i)*
                    $($o)*
                }

                test_derive!($name { $($i)* } expands to { $($o)* } no_build);
            }
        };

        ($name:path { $($i:tt)* } expands to { $($o:tt)* } no_build) => {
            {
                let i = stringify!( $($i)* );
                let parsed = $crate::macros::syn::parse_derive_input(i)
                    .expect(concat!("Failed to parse input to `#[derive(",
                                    stringify!($name),
                                    ")]`"));

                // NOTE: These outputs can get quite long, so we'd like to avoid
                // recursive macros like `quote!` for parsing them. Instead, we use
                // stringify (which is inconsistent with whitespace), split on
                // whitespace, and compare the lists of tokens.

                let res = $name($crate::Structure::new(&parsed));
                let expected = stringify!( $($o)* );

                let res_toks = res.as_str()
                    .split(|ch: char| ch.is_whitespace())
                    .filter(|s: &&str| !s.is_empty())
                    .collect::<Vec<&str>>();

                let exp_toks = expected
                    .split(|ch: char| ch.is_whitespace())
                    .filter(|s: &&str| !s.is_empty())
                    .collect::<Vec<&str>>();

                assert_eq!(
                    res_toks,
                    exp_toks
                )
            }
        };
    }

    /// A helper macro for declaring relatively straightforward derive
    /// implementations. It provides mechanisms for operating over structures
    /// performing modifications on each field etc.
    ///
    /// This macro is a helper wrapper over decl_derive!.
    ///
    /// # Warning
    ///
    /// This is an unstable experimental macro API, which may be changed or removed
    /// in a future version. I'm not yet confident enough that this API is useful
    /// enough to warrant its complexity and inclusion in synstructure.
    ///
    /// # Note
    ///
    /// This feature is implemented behind the `simple-derive` feature, and is only
    /// avaliable when that feature is enabled.
    ///
    /// # Example
    /// ```ignore
    /// simple_derive! {
    ///     // This macro implements the `Interesting` method exported by the `aa`
    ///     // crate. It will explicitly add an `extern crate` invocation to import the
    ///     // crate into the expanded context.
    ///     derive(Interesting) impl ::aa::Interesting {
    ///         // A "filter" block can be added. It evaluates its body with the (s)
    ///         // variable bound to a mutable reference to the input `Structure`
    ///         // object.
    ///         //
    ///         // This block can be used to perform general transformations, such as
    ///         // filtering out fields which should be ignored by all methods and for
    ///         // the purposes of binding type parameters.
    ///         filter(s) {
    ///             s.filter(|bi| bi.ast().ident != Some("a".into()));
    ///         }
    ///
    ///         // This is an implementation of a method in the implemented crate. The
    ///         // return value should be the series of match patterns to destructure
    ///         // the `self` argument with.
    ///         fn is_interesting(&self as s) -> bool {
    ///             s.fold(false, |acc, bi| {
    ///                 quote!(#acc || ::aa::Interesting::is_interesting(#bi))
    ///             })
    ///         }
    ///     }
    /// }
    /// ```
    #[cfg(feature = "simple-derive")]
    #[macro_export]
    macro_rules! simple_derive {
        // entry point
        (
            derive($name:ident) $iname:ident impl $path:path { $($rest:tt)* }
        ) => {
            simple_derive!(@I [$name, $iname, $path] { $($rest)* } [] []);
        };

        // Adding a filter block
        (
            @I $opt:tt {
                filter($s:ident) {
                    $($body:tt)*
                }
                $($rest:tt)*
            } [$($done:tt)*] [$($filter:tt)*]
        ) => {
            simple_derive!(
                @I $opt { $($rest)* } [$($done)*] [
                    $($filter)*
                    [
                        st_name = $s,
                        body = {
                            $($body)*
                        },
                    ]
                ]
            );
        };

        // &self bound method
        (
            @I $opt:tt {
                fn $fn_name:ident (&self as $s:ident $($params:tt)*) $(-> $t:ty)* {
                    $($body:tt)*
                }
                $($rest:tt)*
            } [$($done:tt)*] [$($filter:tt)*]
        ) => {
            simple_derive!(
                @I $opt { $($rest)* } [
                    $($done)*
                    [
                        st_name = $s,
                        bind_style = Ref,
                        body = { $($body)* },
                        result = result,
                        expanded = {
                            fn $fn_name(&self $($params)*) $(-> $t)* {
                                match *self { #result }
                            }
                        },
                    ]
                ] [$($filter)*]
            );
        };

        // &mut self bound method
        (
            @I $opt:tt {
                fn $fn_name:ident (&mut self as $s:ident $($params:tt)*) $(-> $t:ty)* {
                    $($body:tt)*
                }
                $($rest:tt)*
            } [$($done:tt)*] [$($filter:tt)*]
        ) => {
            simple_derive!(
                @I $opt { $($rest)* } [
                    $($done)*
                    [
                        st_name = $s,
                        bind_style = RefMut,
                        body = { $($body)* },
                        result = result,
                        expanded = {
                            fn $fn_name(&mut self $($params)*) $(-> $t)* {
                                match *self { #result }
                            }
                        },
                    ]
                ] [$($filter)*]
            );
        };

        // self bound method
        (
            @I $opt:tt {
                fn $fn_name:ident (self as $s:ident $($params:tt)*) $(-> $t:ty)* {
                    $($body:tt)*
                }
                $($rest:tt)*
            } [$($done:tt)*] [$($filter:tt)*]
        ) => {
            simple_derive!(
                @I $opt { $($rest)* } [
                    $($done)*
                    [
                        st_name = $s,
                        bind_style = Move,
                        body = { $($body)* },
                        result = result,
                        expanded = {
                            fn $fn_name(self $($params)*) $(-> $t)* {
                                match self { #result }
                            }
                        },
                    ]
                ] [$($filter)*]
            );
        };

        // XXX: Static methods?

        // codegen after data collection
        (
            @I [$name:ident, $iname:ident, $path:path] {} [$(
                [
                    st_name = $st_name:ident,
                    bind_style = $bind_style:ident,
                    body = $body:tt,
                    result = $result:ident,
                    expanded = { $($expanded:tt)* },
                ]
            )*] [$(
                [
                    st_name = $filter_st_name:ident,
                    body = $filter_body:tt,
                ]
            )*]
        ) => {
            decl_derive!([$name] => $iname);
            fn $iname(mut st: $crate::Structure) -> $crate::macros::quote::Tokens {
                let _ = &mut st; // Silence the unused mut warning

                // Filter/transform the `Structure` object before cloning it for
                // individual methods.
                $(
                    {
                        let $filter_st_name = &mut st;
                        $filter_body
                    }
                )*

                // Clone the `Structure` object and set the correct binding style,
                // then perform method specific expansion.
                $(
                    let $result = {
                        let mut $st_name = st.clone();
                        $st_name.bind_with(|_| ::synstructure::BindStyle::$bind_style);
                        let $result = {
                            $body
                        };
                        quote!{ $($expanded)* }
                    };
                )*

                st.bound_impl(stringify!($path), quote!{
                    $(#$result)*
                })
            }
        }
    }

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