1 files changed, 116 insertions, 0 deletions
diff --git a/rand/rand-derive/src/lib.rs b/rand/rand-derive/src/lib.rs
new file mode 100644
index 0000000..80c803a
--- /dev/null
+++ b/rand/rand-derive/src/lib.rs
@@ -0,0 +1,116 @@
+//! Support for `#[derive(Rand)]`
+//!
+//! # Examples
+//!
+//! ```
+//! extern crate rand;
+//! #[macro_use]
+//! extern crate rand_derive;
+//!
+//! #[derive(Rand, Debug)]
+//! struct MyStruct {
+//!     a: i32,
+//!     b: u32,
+//! }
+//!
+//! fn main() {
+//!     println!("{:?}", rand::random::<MyStruct>());
+//! }
+//! ```
+
+extern crate proc_macro;
+#[macro_use]
+extern crate quote;
+extern crate syn;
+
+use proc_macro::TokenStream;
+
+#[proc_macro_derive(Rand)]
+pub fn rand_derive(input: TokenStream) -> TokenStream {
+    let s = input.to_string();
+    let ast = syn::parse_derive_input(&s).unwrap();
+    let gen = impl_rand_derive(&ast);
+    gen.parse().unwrap()
+}
+
+fn impl_rand_derive(ast: &syn::MacroInput) -> quote::Tokens {
+    let name = &ast.ident;
+    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
+
+    let rand = match ast.body {
+        syn::Body::Struct(syn::VariantData::Struct(ref body)) => {
+            let fields = body
+                .iter()
+                .filter_map(|field| field.ident.as_ref())
+                .map(|ident| quote! { #ident: __rng.gen() })
+                .collect::<Vec<_>>();
+
+            quote! { #name { #(#fields,)* } }
+        },
+        syn::Body::Struct(syn::VariantData::Tuple(ref body)) => {
+            let fields = (0..body.len())
+                .map(|_| quote! { __rng.gen() })
+                .collect::<Vec<_>>();
+
+            quote! { #name (#(#fields),*) }
+        },
+        syn::Body::Struct(syn::VariantData::Unit) => {
+            quote! { #name }
+        },
+        syn::Body::Enum(ref body) => {
+            if body.is_empty() {
+                panic!("`Rand` cannot be derived for enums with no variants");
+            }
+
+            let len = body.len();
+            let mut arms = body
+                .iter()
+                .map(|variant| {
+                    let ident = &variant.ident;
+                    match variant.data {
+                        syn::VariantData::Struct(ref body) => {
+                            let fields = body
+                                .iter()
+                                .filter_map(|field| field.ident.as_ref())
+                                .map(|ident| quote! { #ident: __rng.gen() })
+                                .collect::<Vec<_>>();
+                            quote! { #name::#ident { #(#fields,)* } }
+                        },
+                        syn::VariantData::Tuple(ref body) => {
+                            let fields = (0..body.len())
+                                .map(|_| quote! { __rng.gen() })
+                                .collect::<Vec<_>>();
+
+                            quote! { #name::#ident (#(#fields),*) }
+                        },
+                        syn::VariantData::Unit => quote! { #name::#ident }
+                    }
+                });
+
+            match len {
+                1 => quote! { #(#arms)* },
+                2 => {
+                    let (a, b) = (arms.next(), arms.next());
+                    quote! { if __rng.gen() { #a } else { #b } }
+                },
+                _ => {
+                    let mut variants = arms
+                        .enumerate()
+                        .map(|(index, arm)| quote! { #index => #arm })
+                        .collect::<Vec<_>>();
+                    variants.push(quote! { _ => unreachable!() });
+                    quote! { match __rng.gen_range(0, #len) { #(#variants,)* } }
+                },
+            }
+        }
+    };
+
+    quote! {
+        impl #impl_generics ::rand::Rand for #name #ty_generics #where_clause {
+            #[inline]
+            fn rand<__R: ::rand::Rng>(__rng: &mut __R) -> Self {
+                #rand
+            }
+        }
+    }
+}