Export the #[derive(FromPrimitive)] from rust proper

.gitignore

@@ -1,2 +1,4 @@
-/target
 /Cargo.lock
+/num_macros/Cargo.lock
+/num_macros/target
+/target

Cargo.toml

@@ -16,3 +16,7 @@ rational, and complex types.
 [dependencies]
 rustc-serialize = "0.3.5"
 rand = "0.3.3"
+
+[dev-dependencies.num_macros]
+path = "num_macros/"
+version = "0.1.22"

num_macros/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "num_macros"
+version = "0.1.22"
+authors = ["The Rust Project Developers"]
+license = "MIT/Apache-2.0"
+homepage = "https://github.com/rust-lang/num"
+repository = "https://github.com/rust-lang/num"
+documentation = "http://doc.rust-lang.org/num"
+keywords = ["mathematics", "numerics"]
+description = """
+Numeric syntax extensions.
+"""
+
+[lib]
+name = "num_macros"
+plugin = true

num_macros/src/lib.rs

@@ -0,0 +1,200 @@
+// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(plugin_registrar, rustc_private)]
+
+extern crate syntax;
+extern crate rustc;
+
+use syntax::ast::{MetaItem, Item, Expr};
+use syntax::ast;
+use syntax::codemap::Span;
+use syntax::ext::base::ExtCtxt;
+use syntax::ext::build::AstBuilder;
+use syntax::ext::deriving::generic::*;
+use syntax::ext::deriving::generic::ty::*;
+use syntax::parse::token::InternedString;
+use syntax::ptr::P;
+use syntax::ext::base::Decorator;
+use syntax::parse::token;
+
+use rustc::plugin::Registry;
+
+macro_rules! pathvec {
+    ($($x:ident)::+) => (
+        vec![ $( stringify!($x) ),+ ]
+    )
+}
+
+macro_rules! path {
+    ($($x:tt)*) => (
+        ::syntax::ext::deriving::generic::ty::Path::new( pathvec!( $($x)* ) )
+    )
+}
+
+macro_rules! path_local {
+    ($x:ident) => (
+        ::syntax::ext::deriving::generic::ty::Path::new_local(stringify!($x))
+    )
+}
+
+macro_rules! pathvec_std {
+    ($cx:expr, $first:ident :: $($rest:ident)::+) => (
+        if $cx.use_std {
+            pathvec!(std :: $($rest)::+)
+        } else {
+            pathvec!($first :: $($rest)::+)
+        }
+    )
+}
+
+macro_rules! path_std {
+    ($($x:tt)*) => (
+        ::syntax::ext::deriving::generic::ty::Path::new( pathvec_std!( $($x)* ) )
+    )
+}
+
+pub fn expand_deriving_from_primitive(cx: &mut ExtCtxt,
+                                      span: Span,
+                                      mitem: &MetaItem,
+                                      item: &Item,
+                                      push: &mut FnMut(P<Item>))
+{
+    let inline = cx.meta_word(span, InternedString::new("inline"));
+    let attrs = vec!(cx.attribute(span, inline));
+    let trait_def = TraitDef {
+        span: span,
+        attributes: Vec::new(),
+        path: path!(num::FromPrimitive),
+        additional_bounds: Vec::new(),
+        generics: LifetimeBounds::empty(),
+        methods: vec!(
+            MethodDef {
+                name: "from_i64",
+                generics: LifetimeBounds::empty(),
+                explicit_self: None,
+                args: vec!(Literal(path_local!(i64))),
+                ret_ty: Literal(Path::new_(pathvec_std!(cx, core::option::Option),
+                                           None,
+                                           vec!(Box::new(Self_)),
+                                           true)),
+                // #[inline] liable to cause code-bloat
+                attributes: attrs.clone(),
+                combine_substructure: combine_substructure(Box::new(|c, s, sub| {
+                    cs_from("i64", c, s, sub)
+                })),
+            },
+            MethodDef {
+                name: "from_u64",
+                generics: LifetimeBounds::empty(),
+                explicit_self: None,
+                args: vec!(Literal(path_local!(u64))),
+                ret_ty: Literal(Path::new_(pathvec_std!(cx, core::option::Option),
+                                           None,
+                                           vec!(Box::new(Self_)),
+                                           true)),
+                // #[inline] liable to cause code-bloat
+                attributes: attrs,
+                combine_substructure: combine_substructure(Box::new(|c, s, sub| {
+                    cs_from("u64", c, s, sub)
+                })),
+            }
+        ),
+        associated_types: Vec::new(),
+    };
+
+    trait_def.expand(cx, mitem, item, push)
+}
+
+fn cs_from(name: &str, cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
+    if substr.nonself_args.len() != 1 {
+        cx.span_bug(trait_span, "incorrect number of arguments in `derive(FromPrimitive)`")
+    }
+
+    let n = &substr.nonself_args[0];
+
+    match *substr.fields {
+        StaticStruct(..) => {
+            cx.span_err(trait_span, "`FromPrimitive` cannot be derived for structs");
+            return cx.expr_fail(trait_span, InternedString::new(""));
+        }
+        StaticEnum(enum_def, _) => {
+            if enum_def.variants.is_empty() {
+                cx.span_err(trait_span,
+                            "`FromPrimitive` cannot be derived for enums with no variants");
+                return cx.expr_fail(trait_span, InternedString::new(""));
+            }
+
+            let mut arms = Vec::new();
+
+            for variant in &enum_def.variants {
+                match variant.node.kind {
+                    ast::TupleVariantKind(ref args) => {
+                        if !args.is_empty() {
+                            cx.span_err(trait_span,
+                                        "`FromPrimitive` cannot be derived for \
+                                        enum variants with arguments");
+                            return cx.expr_fail(trait_span,
+                                                InternedString::new(""));
+                        }
+                        let span = variant.span;
+
+                        // expr for `$n == $variant as $name`
+                        let path = cx.path(span, vec![substr.type_ident, variant.node.name]);
+                        let variant = cx.expr_path(path);
+                        let ty = cx.ty_ident(span, cx.ident_of(name));
+                        let cast = cx.expr_cast(span, variant.clone(), ty);
+                        let guard = cx.expr_binary(span, ast::BiEq, n.clone(), cast);
+
+                        // expr for `Some($variant)`
+                        let body = cx.expr_some(span, variant);
+
+                        // arm for `_ if $guard => $body`
+                        let arm = ast::Arm {
+                            attrs: vec!(),
+                            pats: vec!(cx.pat_wild(span)),
+                            guard: Some(guard),
+                            body: body,
+                        };
+
+                        arms.push(arm);
+                    }
+                    ast::StructVariantKind(_) => {
+                        cx.span_err(trait_span,
+                                    "`FromPrimitive` cannot be derived for enums \
+                                    with struct variants");
+                        return cx.expr_fail(trait_span,
+                                            InternedString::new(""));
+                    }
+                }
+            }
+
+            // arm for `_ => None`
+            let arm = ast::Arm {
+                attrs: vec!(),
+                pats: vec!(cx.pat_wild(trait_span)),
+                guard: None,
+                body: cx.expr_none(trait_span),
+            };
+            arms.push(arm);
+
+            cx.expr_match(trait_span, n.clone(), arms)
+        }
+        _ => cx.span_bug(trait_span, "expected StaticEnum in derive(FromPrimitive)")
+    }
+}
+
+#[plugin_registrar]
+#[doc(hidden)]
+pub fn plugin_registrar(reg: &mut Registry) {
+    reg.register_syntax_extension(
+        token::intern("derive_NumFromPrimitive"),
+        Decorator(Box::new(expand_deriving_from_primitive)));
+}

tests/test_macro.rs

@@ -0,0 +1,36 @@
+// Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(custom_derive, plugin)]
+#![plugin(num_macros)]
+
+extern crate num;
+
+#[derive(Debug, PartialEq, NumFromPrimitive)]
+enum Color {
+    Red,
+    Blue,
+    Green,
+}
+
+#[test]
+fn test_from_primitive() {
+    let v: Vec<Option<Color>> = vec![
+        num::FromPrimitive::from_u64(0),
+        num::FromPrimitive::from_u64(1),
+        num::FromPrimitive::from_u64(2),
+        num::FromPrimitive::from_u64(3),
+    ];
+
+    assert_eq!(
+        v,
+        vec![Some(Color::Red), Some(Color::Blue), Some(Color::Green), None]
+    );
+}