Auto merge of #31400 - durka:civilized-deriving, r=alexcrichton

You can `#[derive(FromPrimitive)]`, but it [fails later in the compile](https://play.rust-lang.org/?gist=82cb8ad2fac49e3fe472&version=stable) due to hardcoding `std::num::FromPrimitive` which [was removed](https://github.com/rust-lang/rust/commit/eeb94886adccb3f13003f92f117115d17846ce1f) (for some reason Github doesn't show `FromPrimitive` in the diff, but `git show` does).

Anyway, this PR removes the code. I didn't mark it as a breaking change, even though [this extremely contrived code using highly unstable features](https://play.rust-lang.org/?gist=1e1b1bbff962837b228a&version=nightly) is broken by it -- should I?

3 files changed, 4 insertions, 168 deletions

diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index 919540724ca..dcaa9644603 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -63,7 +63,6 @@ pub mod decodable;
 pub mod hash;
 pub mod debug;
 pub mod default;
-pub mod primitive;
 
 #[path="cmp/partial_eq.rs"]
 pub mod partial_eq;
@@ -178,8 +177,6 @@ derive_traits! {
 
     "Default" => default::expand_deriving_default,
 
-    "FromPrimitive" => primitive::expand_deriving_from_primitive,
-
     "Send" => bounds::expand_deriving_unsafe_bound,
     "Sync" => bounds::expand_deriving_unsafe_bound,
     "Copy" => bounds::expand_deriving_copy,
diff --git a/src/libsyntax_ext/deriving/primitive.rs b/src/libsyntax_ext/deriving/primitive.rs
deleted file mode 100644
index 121fe01976e..00000000000
--- a/src/libsyntax_ext/deriving/primitive.rs
+++ /dev/null
@@ -1,142 +0,0 @@
-// Copyright 2012-2013 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.
-
-use deriving::generic::*;
-use deriving::generic::ty::*;
-
-use syntax::ast::{MetaItem, Expr};
-use syntax::ast;
-use syntax::codemap::Span;
-use syntax::ext::base::{ExtCtxt, Annotatable};
-use syntax::ext::build::AstBuilder;
-use syntax::parse::token::InternedString;
-use syntax::ptr::P;
-
-pub fn expand_deriving_from_primitive(cx: &mut ExtCtxt,
-                                      span: Span,
-                                      mitem: &MetaItem,
-                                      item: &Annotatable,
-                                      push: &mut FnMut(Annotatable))
-{
-    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_std!(cx, core::num::FromPrimitive),
-        additional_bounds: Vec::new(),
-        generics: LifetimeBounds::empty(),
-        is_unsafe: false,
-        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(),
-                is_unsafe: false,
-                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,
-                is_unsafe: false,
-                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> {
-    let n = match (substr.nonself_args.len(), substr.nonself_args.get(0)) {
-        (1, Some(o_f)) => o_f,
-        _ => cx.span_bug(trait_span, "incorrect number of arguments in `derive(FromPrimitive)`")
-    };
-
-    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 {
-                let def = &variant.node.data;
-                if !def.is_unit() {
-                    cx.span_err(trait_span, "`FromPrimitive` cannot be derived \
-                                             for enums with non-unit variants");
-                    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);
-            }
-
-            // 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)")
-    }
-}
diff --git a/src/test/compile-fail/deriving-primitive.rs b/src/test/compile-fail/deriving-primitive.rs
index e8e37d88049..be822a173ab 100644
--- a/src/test/compile-fail/deriving-primitive.rs
+++ b/src/test/compile-fail/deriving-primitive.rs
@@ -1,4 +1,4 @@
-// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -8,27 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::num::FromPrimitive;
-use std::isize;
+#[derive(FromPrimitive)] //~ERROR `#[derive]` for custom traits is not stable
+enum Foo {}
 
-#[derive(FromPrimitive)]
-struct A { x: isize }
-//~^^ ERROR `FromPrimitive` cannot be derived for structs
-//~^^^ ERROR `FromPrimitive` cannot be derived for structs
+fn main() {}
 
-#[derive(FromPrimitive)]
-struct B(isize);
-//~^^ ERROR `FromPrimitive` cannot be derived for structs
-//~^^^ ERROR `FromPrimitive` cannot be derived for structs
-
-#[derive(FromPrimitive)]
-enum C { Foo(isize), Bar(usize) }
-//~^^ ERROR `FromPrimitive` cannot be derived for enums with non-unit variants
-//~^^^ ERROR `FromPrimitive` cannot be derived for enums with non-unit variants
-
-#[derive(FromPrimitive)]
-enum D { Baz { x: isize } }
-//~^^ ERROR `FromPrimitive` cannot be derived for enums with non-unit variants
-//~^^^ ERROR `FromPrimitive` cannot be derived for enums with non-unit variants
-
-pub fn main() {}