From 31f5ab3f0c59f65e6758fe5ffadb617a98dcd5b4 Mon Sep 17 00:00:00 2001
From: Nick Cameron <ncameron@mozilla.com>
Date: Sun, 14 Dec 2014 15:42:41 +1300
Subject: [PATCH] Allow `Self` in impls.

---
 src/libsyntax/ext/base.rs      |  2 +-
 src/libsyntax/ext/expand.rs    | 51 +++++++++++++++++++++++++++++++---
 src/test/run-pass/self-impl.rs | 42 ++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+), 5 deletions(-)
 create mode 100644 src/test/run-pass/self-impl.rs

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 3947a602809..aefbb2a1fea 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -490,7 +490,7 @@ impl<'a> ExtCtxt<'a> {
 
     /// Returns a `Folder` for deeply expanding all macros in a AST node.
     pub fn expander<'b>(&'b mut self) -> expand::MacroExpander<'b, 'a> {
-        expand::MacroExpander { cx: self }
+        expand::MacroExpander::new(self)
     }
 
     pub fn new_parser_from_tts(&self, tts: &[ast::TokenTree])
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 20c8ff20b71..01d55eba316 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -15,6 +15,7 @@ use ast::{ItemMac, MacStmtWithSemicolon, Mrk, Stmt, StmtDecl, StmtMac};
 use ast::{StmtExpr, StmtSemi};
 use ast::TokenTree;
 use ast;
+use ast_util::path_to_ident;
 use ext::mtwt;
 use ext::build::AstBuilder;
 use attr;
@@ -37,6 +38,30 @@ enum Either<L,R> {
     Right(R)
 }
 
+pub fn expand_type(t: P<ast::Ty>,
+                   fld: &mut MacroExpander,
+                   impl_ty: Option<P<ast::Ty>>)
+                   -> P<ast::Ty> {
+    debug!("expanding type {} with impl_ty {}", t, impl_ty);
+    let t = match (t.node.clone(), impl_ty) {
+        // Expand uses of `Self` in impls to the concrete type.
+        (ast::Ty_::TyPath(ref path, _), Some(ref impl_ty)) => {
+            let path_as_ident = path_to_ident(path);
+            // Note unhygenic comparison here. I think this is correct, since
+            // even though `Self` is almost just a type parameter, the treatment
+            // for this expansion is as if it were a keyword.
+            if path_as_ident.is_some() &&
+               path_as_ident.unwrap().name == token::special_idents::type_self.name {
+                impl_ty.clone()
+            } else {
+                t
+            }
+        }
+        _ => t
+    };
+    fold::noop_fold_ty(t, fld)
+}
+
 pub fn expand_expr(e: P<ast::Expr>, fld: &mut MacroExpander) -> P<ast::Expr> {
     e.and_then(|ast::Expr {id, node, span}| match node {
         // expr_mac should really be expr_ext or something; it's the
@@ -1059,6 +1084,14 @@ fn expand_and_rename_fn_decl_and_block(fn_decl: P<ast::FnDecl>, block: P<ast::Bl
 /// A tree-folder that performs macro expansion
 pub struct MacroExpander<'a, 'b:'a> {
     pub cx: &'a mut ExtCtxt<'b>,
+    // The type of the impl currently being expanded.
+    current_impl_type: Option<P<ast::Ty>>,
+}
+
+impl<'a, 'b> MacroExpander<'a, 'b> {
+    pub fn new(cx: &'a mut ExtCtxt<'b>) -> MacroExpander<'a, 'b> {
+        MacroExpander { cx: cx, current_impl_type: None }
+    }
 }
 
 impl<'a, 'b> Folder for MacroExpander<'a, 'b> {
@@ -1071,7 +1104,14 @@ impl<'a, 'b> Folder for MacroExpander<'a, 'b> {
     }
 
     fn fold_item(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
-        expand_item(item, self)
+        let prev_type = self.current_impl_type.clone();
+        if let ast::Item_::ItemImpl(_, _, _, ref ty, _) = item.node {
+            self.current_impl_type = Some(ty.clone());
+        }
+
+        let result = expand_item(item, self);
+        self.current_impl_type = prev_type;
+        result
     }
 
     fn fold_item_underscore(&mut self, item: ast::Item_) -> ast::Item_ {
@@ -1094,6 +1134,11 @@ impl<'a, 'b> Folder for MacroExpander<'a, 'b> {
         expand_method(method, self)
     }
 
+    fn fold_ty(&mut self, t: P<ast::Ty>) -> P<ast::Ty> {
+        let impl_type = self.current_impl_type.clone();
+        expand_type(t, self, impl_type)
+    }
+
     fn new_span(&mut self, span: Span) -> Span {
         new_span(self.cx, span)
     }
@@ -1138,9 +1183,7 @@ pub fn expand_crate(parse_sess: &parse::ParseSess,
                     user_exts: Vec<NamedSyntaxExtension>,
                     c: Crate) -> Crate {
     let mut cx = ExtCtxt::new(parse_sess, c.config.clone(), cfg);
-    let mut expander = MacroExpander {
-        cx: &mut cx,
-    };
+    let mut expander = MacroExpander::new(&mut cx);
 
     for ExportedMacros { crate_name, macros } in imported_macros.into_iter() {
         let name = format!("<{} macros>", token::get_ident(crate_name))
diff --git a/src/test/run-pass/self-impl.rs b/src/test/run-pass/self-impl.rs
new file mode 100644
index 00000000000..3ece042aef0
--- /dev/null
+++ b/src/test/run-pass/self-impl.rs
@@ -0,0 +1,42 @@
+// Copyright 2014 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.
+
+// Test that we can use `Self` types in impls in the expected way.
+
+struct Foo;
+
+// Test uses on inherant impl.
+impl Foo {
+    fn foo(_x: Self, _y: &Self, _z: Box<Self>) -> Self {
+        Foo
+    }
+}
+
+// Test uses when implementing a trait and with a type parameter.
+pub struct Baz<X> {
+    pub f: X,
+}
+
+trait Bar<X> {
+    fn bar(x: Self, y: &Self, z: Box<Self>) -> Self;
+}
+
+impl Bar<int> for Box<Baz<int>> {
+    fn bar(_x: Self, _y: &Self, _z: Box<Self>) -> Self {
+        box Baz { f: 42 }
+    }
+}
+
+fn main() {
+    let _: Foo = Foo::foo(Foo, &Foo, box Foo);
+    let _: Box<Baz<int>> = Bar::bar(box Baz { f: 42 },
+                                    &box Baz { f: 42 },
+                                    box box Baz { f: 42 });
+}