From 6f8b476d34eebd2e0f6dfc59fbef40f500b0ffcf Mon Sep 17 00:00:00 2001
From: Erick Tryzelaar <erick.tryzelaar@gmail.com>
Date: Thu, 24 Dec 2015 11:21:29 -0500
Subject: [PATCH] fix(derive): Restore #[derive] functionality

In the core rust repo, this was migrated into a separate crate.
I don't think it's necessary to replicate that crate since
all we want is #[derive] support.
---
 syntex_syntax/src/ext/base.rs         |   4 +
 syntex_syntax/src/ext/deriving/mod.rs | 107 ++++++++++++++++++++++++++
 syntex_syntax/src/lib.rs              |   1 +
 3 files changed, 112 insertions(+)
 create mode 100644 syntex_syntax/src/ext/deriving/mod.rs

diff --git a/syntex_syntax/src/ext/base.rs b/syntex_syntax/src/ext/base.rs
index 6f1d828a..e5cb1880 100644
--- a/syntex_syntax/src/ext/base.rs
+++ b/syntex_syntax/src/ext/base.rs
@@ -466,7 +466,11 @@ fn initial_syntax_expander_table<'feat>(_ecfg: &expand::ExpansionConfig<'feat>)
 
     /*
     syntax_expanders.insert(intern("macro_rules"), MacroRulesTT);
+    */
+
+    ext::deriving::register_all(&mut syntax_expanders);
 
+    /*
     if ecfg.enable_quotes() {
         // Quasi-quoting expanders
         syntax_expanders.insert(intern("quote_tokens"),
diff --git a/syntex_syntax/src/ext/deriving/mod.rs b/syntex_syntax/src/ext/deriving/mod.rs
new file mode 100644
index 00000000..b95aedda
--- /dev/null
+++ b/syntex_syntax/src/ext/deriving/mod.rs
@@ -0,0 +1,107 @@
+// 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.
+
+//! The compiler code necessary to implement the `#[derive]` extensions.
+//!
+//! FIXME (#2810): hygiene. Search for "__" strings (in other files too). We also assume "extra" is
+//! the standard library, and "std" is the core library.
+
+use ast::{MetaItem, MetaWord};
+use attr::AttrMetaMethods;
+use ext::base::{ExtCtxt, SyntaxEnv, MultiModifier, Annotatable};
+use ext::build::AstBuilder;
+use feature_gate;
+use codemap::Span;
+use parse::token::{intern, intern_and_get_ident};
+
+fn expand_derive(cx: &mut ExtCtxt,
+                 span: Span,
+                 mitem: &MetaItem,
+                 annotatable: Annotatable)
+                 -> Annotatable {
+    annotatable.map_item_or(|item| {
+        item.map(|mut item| {
+            if mitem.value_str().is_some() {
+                cx.span_err(mitem.span, "unexpected value in `derive`");
+            }
+
+            let traits = mitem.meta_item_list().unwrap_or(&[]);
+            if traits.is_empty() {
+                cx.span_warn(mitem.span, "empty trait list in `derive`");
+            }
+
+            for titem in traits.iter().rev() {
+                let tname = match titem.node {
+                    MetaWord(ref tname) => tname,
+                    _ => {
+                        cx.span_err(titem.span, "malformed `derive` entry");
+                        continue;
+                    }
+                };
+
+                if !(is_builtin_trait(tname) || cx.ecfg.enable_custom_derive()) {
+                    feature_gate::emit_feature_err(&cx.parse_sess.span_diagnostic,
+                                                   "custom_derive",
+                                                   titem.span,
+                                                   feature_gate::GateIssue::Language,
+                                                   feature_gate::EXPLAIN_CUSTOM_DERIVE);
+                    continue;
+                }
+
+                // #[derive(Foo, Bar)] expands to #[derive_Foo] #[derive_Bar]
+                item.attrs.push(cx.attribute(titem.span, cx.meta_word(titem.span,
+                    intern_and_get_ident(&format!("derive_{}", tname)))));
+            }
+
+            item
+        })
+    }, |a| {
+        cx.span_err(span, "`derive` can only be applied to items");
+        a
+    })
+}
+
+pub fn register_all(env: &mut SyntaxEnv) {
+    env.insert(intern("derive"),
+               MultiModifier(Box::new(expand_derive)));
+}
+
+fn is_builtin_trait(name: &str) -> bool {
+    match name {
+        "Clone" => true,
+
+        "Hash" => true,
+
+        "RustcEncodable" => true,
+
+        "RustcDecodable" => true,
+
+        "PartialEq" => true,
+        "Eq" => true,
+        "PartialOrd" => true,
+        "Ord" => true,
+
+        "Debug" => true,
+
+        "Default" => true,
+
+        "FromPrimitive" => true,
+
+        "Send" => true,
+        "Sync" => true,
+        "Copy" => true,
+
+        // deprecated
+        "Encodable" => true,
+        "Decodable" => true,
+
+        _ => false,
+    }
+}
diff --git a/syntex_syntax/src/lib.rs b/syntex_syntax/src/lib.rs
index 616b5c37..4f5f439e 100644
--- a/syntex_syntax/src/lib.rs
+++ b/syntex_syntax/src/lib.rs
@@ -97,6 +97,7 @@ pub mod print {
 pub mod ext {
     pub mod base;
     pub mod build;
+    pub mod deriving;
     pub mod expand;
     pub mod mtwt;
     pub mod quote;