reviewer comments and rebasing

9 files changed, 173 insertions, 154 deletions

diff --git a/src/librustc_plugin/registry.rs b/src/librustc_plugin/registry.rs
index f8bce297a42..7b048c0670d 100644
--- a/src/librustc_plugin/registry.rs
+++ b/src/librustc_plugin/registry.rs
@@ -15,8 +15,7 @@ use rustc::session::Session;
 
 use rustc::mir::transform::MirMapPass;
 
-use syntax::ext::base::{SyntaxExtension, NamedSyntaxExtension, NormalTT};
-use syntax::ext::base::{IdentTT, MultiModifier, MultiDecorator};
+use syntax::ext::base::{SyntaxExtension, NamedSyntaxExtension, NormalTT, IdentTT};
 use syntax::ext::base::MacroExpanderFn;
 use syntax::parse::token;
 use syntax::ast;
@@ -109,10 +108,7 @@ impl<'a> Registry<'a> {
             IdentTT(ext, _, allow_internal_unstable) => {
                 IdentTT(ext, Some(self.krate_span), allow_internal_unstable)
             }
-            MultiDecorator(ext) => MultiDecorator(ext),
-            MultiModifier(ext) => MultiModifier(ext),
-            SyntaxExtension::ProcMacro(ext) => SyntaxExtension::ProcMacro(ext),
-            SyntaxExtension::AttrProcMacro(ext) => SyntaxExtension::AttrProcMacro(ext),
+            _ => extension,
         }));
     }
 
diff --git a/src/librustc_resolve/macros.rs b/src/librustc_resolve/macros.rs
index 67ee4c307d3..67e725b6e72 100644
--- a/src/librustc_resolve/macros.rs
+++ b/src/librustc_resolve/macros.rs
@@ -73,7 +73,9 @@ impl<'a> base::Resolver for Resolver<'a> {
             let name = intern(&attrs[i].name());
             match self.expansion_data[0].module.macros.borrow().get(&name) {
                 Some(ext) => match **ext {
-                    MultiModifier(..) | MultiDecorator(..) => return Some(attrs.remove(i)),
+                    MultiModifier(..) | MultiDecorator(..) | SyntaxExtension::AttrProcMacro(..) => {
+                        return Some(attrs.remove(i))
+                    }
                     _ => {}
                 },
                 None => {}
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 82db9ffca83..91742680711 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-pub use self::SyntaxExtension::{MultiDecorator, MultiModifier, NormalTT, IdentTT, MacroRulesTT};
+pub use self::SyntaxExtension::{MultiDecorator, MultiModifier, NormalTT, IdentTT};
 
 use ast::{self, Attribute, Name, PatKind};
 use attr::HasAttrs;
@@ -18,6 +18,7 @@ use errors::DiagnosticBuilder;
 use ext::expand::{self, Invocation, Expansion};
 use ext::hygiene::Mark;
 use ext::tt::macro_rules;
+use fold;
 use parse;
 use parse::parser::{self, Parser};
 use parse::token;
@@ -61,14 +62,6 @@ impl HasAttrs for Annotatable {
 }
 
 impl Annotatable {
-    pub fn span(&self) -> Span {
-        match *self {
-            Annotatable::Item(ref item) => item.span,
-            Annotatable::TraitItem(ref trait_item) => trait_item.span,
-            Annotatable::ImplItem(ref impl_item) => impl_item.span,
-        }
-    }
-
     pub fn expect_item(self) -> P<ast::Item> {
         match self {
             Annotatable::Item(i) => i,
@@ -160,21 +153,19 @@ pub trait ProcMacro {
                    ecx: &'cx mut ExtCtxt,
                    span: Span,
                    ts: TokenStream)
-                   -> Box<MacResult+'cx>;
+                   -> TokenStream;
 }
 
 impl<F> ProcMacro for F
     where F: Fn(TokenStream) -> TokenStream
 {
     fn expand<'cx>(&self,
-                   ecx: &'cx mut ExtCtxt,
-                   span: Span,
+                   _ecx: &'cx mut ExtCtxt,
+                   _span: Span,
                    ts: TokenStream)
-                   -> Box<MacResult+'cx> {
-        let result = (*self)(ts);
+                   -> TokenStream {
         // FIXME setup implicit context in TLS before calling self.
-        let parser = ecx.new_parser_from_tts(&result.to_tts());
-        Box::new(TokResult { parser: parser, span: span })
+        (*self)(ts)
     }
 }
 
@@ -184,50 +175,63 @@ pub trait AttrProcMacro {
                    span: Span,
                    annotation: TokenStream,
                    annotated: TokenStream)
-                   -> Box<MacResult+'cx>;
+                   -> TokenStream;
 }
 
 impl<F> AttrProcMacro for F
     where F: Fn(TokenStream, TokenStream) -> TokenStream
 {
     fn expand<'cx>(&self,
-                   ecx: &'cx mut ExtCtxt,
-                   span: Span,
+                   _ecx: &'cx mut ExtCtxt,
+                   _span: Span,
                    annotation: TokenStream,
                    annotated: TokenStream)
-                   -> Box<MacResult+'cx> {
+                   -> TokenStream {
         // FIXME setup implicit context in TLS before calling self.
-        let parser = ecx.new_parser_from_tts(&(*self)(annotation, annotated).to_tts());
-        Box::new(TokResult { parser: parser, span: span })
+        (*self)(annotation, annotated)
     }
 }
 
-struct TokResult<'a> {
-    parser: Parser<'a>,
-    span: Span,
+pub struct TokResult<'a> {
+    pub parser: Parser<'a>,
+    pub span: Span,
+}
+
+impl<'a> TokResult<'a> {
+    // There is quite a lot of overlap here with ParserAnyMacro in ext/tt/macro_rules.rs
+    // We could probably share more code.
+    // FIXME(#36641) Unify TokResult and ParserAnyMacro.
+    fn ensure_complete_parse(&mut self, allow_semi: bool) {
+        let macro_span = &self.span;
+        self.parser.ensure_complete_parse(allow_semi, |parser| {
+            let token_str = parser.this_token_to_string();
+            let msg = format!("macro expansion ignores token `{}` and any following", token_str);
+            let span = parser.span;
+            parser.diagnostic()
+                  .struct_span_err(span, &msg)
+                  .span_note(*macro_span, "caused by the macro expansion here")
+                  .emit();
+        });
+    }
 }
 
 impl<'a> MacResult for TokResult<'a> {
     fn make_items(mut self: Box<Self>) -> Option<SmallVector<P<ast::Item>>> {
         if self.parser.sess.span_diagnostic.has_errors() {
-            return None;
+            return Some(SmallVector::zero());
         }
 
         let mut items = SmallVector::zero();
         loop {
             match self.parser.parse_item() {
-                Ok(Some(item)) => {
-                    // FIXME better span info.
-                    let mut item = item.unwrap();
-                    item.span = self.span;
-                    items.push(P(item));
-                }
+                Ok(Some(item)) => items.push(item),
                 Ok(None) => {
+                    self.ensure_complete_parse(false);
                     return Some(items);
                 }
                 Err(mut e) => {
                     e.emit();
-                    return None;
+                    return Some(SmallVector::zero());
                 }
             }
         }
@@ -236,57 +240,61 @@ impl<'a> MacResult for TokResult<'a> {
     fn make_impl_items(mut self: Box<Self>) -> Option<SmallVector<ast::ImplItem>> {
         let mut items = SmallVector::zero();
         loop {
+            if self.parser.token == token::Eof {
+                break;
+            }
             match self.parser.parse_impl_item() {
-                Ok(mut item) => {
-                    // FIXME better span info.
-                    item.span = self.span;
-                    items.push(item);
-
-                    return Some(items);
-                }
+                Ok(item) => items.push(item),
                 Err(mut e) => {
                     e.emit();
-                    return None;
+                    return Some(SmallVector::zero());
                 }
             }
         }
+        self.ensure_complete_parse(false);
+        Some(items)
     }
 
     fn make_trait_items(mut self: Box<Self>) -> Option<SmallVector<ast::TraitItem>> {
         let mut items = SmallVector::zero();
         loop {
+            if self.parser.token == token::Eof {
+                break;
+            }
             match self.parser.parse_trait_item() {
-                Ok(mut item) => {
-                    // FIXME better span info.
-                    item.span = self.span;
-                    items.push(item);
-
-                    return Some(items);
-                }
+                Ok(item) => items.push(item),
                 Err(mut e) => {
                     e.emit();
-                    return None;
+                    return Some(SmallVector::zero());
                 }
             }
         }
+        self.ensure_complete_parse(false);
+        Some(items)
     }
 
     fn make_expr(mut self: Box<Self>) -> Option<P<ast::Expr>> {
         match self.parser.parse_expr() {
-            Ok(e) => Some(e),
+            Ok(e) => {
+                self.ensure_complete_parse(true);
+                Some(e)
+            }
             Err(mut e) => {
                 e.emit();
-                return None;
+                Some(DummyResult::raw_expr(self.span))
             }
         }
     }
 
     fn make_pat(mut self: Box<Self>) -> Option<P<ast::Pat>> {
         match self.parser.parse_pat() {
-            Ok(e) => Some(e),
+            Ok(e) => {
+                self.ensure_complete_parse(false);
+                Some(e)
+            }
             Err(mut e) => {
                 e.emit();
-                return None;
+                Some(P(DummyResult::raw_pat(self.span)))
             }
         }
     }
@@ -295,28 +303,30 @@ impl<'a> MacResult for TokResult<'a> {
         let mut stmts = SmallVector::zero();
         loop {
             if self.parser.token == token::Eof {
-                return Some(stmts);
+                break;
             }
-            match self.parser.parse_full_stmt(true) {
-                Ok(Some(mut stmt)) => {
-                    stmt.span = self.span;
-                    stmts.push(stmt);
-                }
+            match self.parser.parse_full_stmt(false) {
+                Ok(Some(stmt)) => stmts.push(stmt),
                 Ok(None) => { /* continue */ }
                 Err(mut e) => {
                     e.emit();
-                    return None;
+                    return Some(SmallVector::zero());
                 }
             }
         }
+        self.ensure_complete_parse(false);
+        Some(stmts)
     }
 
     fn make_ty(mut self: Box<Self>) -> Option<P<ast::Ty>> {
         match self.parser.parse_ty() {
-            Ok(e) => Some(e),
+            Ok(e) => {
+                self.ensure_complete_parse(false);
+                Some(e)
+            }
             Err(mut e) => {
                 e.emit();
-                return None;
+                Some(DummyResult::raw_ty(self.span))
             }
         }
     }
@@ -1004,3 +1014,17 @@ pub fn get_exprs_from_tts(cx: &mut ExtCtxt,
     }
     Some(es)
 }
+
+pub struct ChangeSpan {
+    pub span: Span
+}
+
+impl Folder for ChangeSpan {
+    fn new_span(&mut self, _sp: Span) -> Span {
+        self.span
+    }
+
+    fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
+        fold::noop_fold_mac(mac, self)
+    }
+}
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index f022dd3a08b..eaa7684d8fb 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -21,8 +21,10 @@ use ext::base::*;
 use feature_gate::{self, Features};
 use fold;
 use fold::*;
+use parse::{ParseSess, lexer};
+use parse::parser::Parser;
 use parse::token::{intern, keywords};
-use parse::span_to_tts;
+use print::pprust;
 use ptr::P;
 use tokenstream::{TokenTree, TokenStream};
 use util::small_vector::SmallVector;
@@ -310,29 +312,18 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 kind.expect_from_annotatables(items)
             }
             SyntaxExtension::AttrProcMacro(ref mac) => {
-                let attr_toks = TokenStream::from_tts(span_to_tts(&fld.cx.parse_sess,
-                                                                  attr.span));
-                let item_toks = TokenStream::from_tts(span_to_tts(&fld.cx.parse_sess,
-                                                                  item.span()));
-                let result = mac.expand(self.cx, attr.span, attr_toks, item_toks);
-                let items = match item {
-                    Annotatable::Item(_) => result.make_items()
-                                                  .unwrap_or(SmallVector::zero())
-                                                  .into_iter()
-                                                  .map(|i| Annotatable::Item(i))
-                                                  .collect(),
-                    Annotatable::TraitItem(_) => result.make_trait_items()
-                                                       .unwrap_or(SmallVector::zero())
-                                                       .into_iter()
-                                                       .map(|i| Annotatable::TraitItem(P(i)))
-                                                       .collect(),
-                    Annotatable::ImplItem(_) => result.make_impl_items()
-                                                      .unwrap_or(SmallVector::zero())
-                                                      .into_iter()
-                                                      .map(|i| Annotatable::ImplItem(P(i)))
-                                                      .collect(),
-                };
-                kind.expect_from_annotatables(items)
+                let attr_toks = TokenStream::from_tts(tts_for_attr(&attr, &self.cx.parse_sess));
+                let item_toks = TokenStream::from_tts(tts_for_item(&item, &self.cx.parse_sess));
+
+                let tok_result = mac.expand(self.cx, attr.span, attr_toks, item_toks);
+                let parser = self.cx.new_parser_from_tts(&tok_result.to_tts());
+                let result = Box::new(TokResult { parser: parser, span: attr.span });
+
+                kind.make_from(result).unwrap_or_else(|| {
+                    let msg = format!("macro could not be expanded into {} position", kind.name());
+                    self.cx.span_err(attr.span, &msg);
+                    kind.dummy(attr.span)
+                })
             }
             _ => unreachable!(),
         }
@@ -413,12 +404,12 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 if ident.name != keywords::Invalid.name() {
                     let msg =
                         format!("macro {}! expects no ident argument, given '{}'", extname, ident);
-                    fld.cx.span_err(path.span, &msg);
-                    return None;
+                    self.cx.span_err(path.span, &msg);
+                    return kind.dummy(span);
                 }
 
-                fld.cx.bt_push(ExpnInfo {
-                    call_site: call_site,
+                self.cx.bt_push(ExpnInfo {
+                    call_site: span,
                     callee: NameAndSpan {
                         format: MacroBang(extname),
                         // FIXME procedural macros do not have proper span info
@@ -429,7 +420,14 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     },
                 });
 
-                Some(expandfun.expand(fld.cx, call_site, TokenStream::from_tts(marked_tts)))
+
+                let tok_result = expandfun.expand(self.cx,
+                                                  span,
+                                                  TokenStream::from_tts(marked_tts));
+                let parser = self.cx.new_parser_from_tts(&tok_result.to_tts());
+                let result = Box::new(TokResult { parser: parser, span: span });
+                // FIXME better span info.
+                kind.make_from(result).map(|i| i.fold_with(&mut ChangeSpan { span: span }))
             }
         };
 
@@ -502,6 +500,36 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     }
 }
 
+// These are pretty nasty. Ideally, we would keep the tokens around, linked from
+// the AST. However, we don't so we need to create new ones. Since the item might
+// have come from a macro expansion (possibly only in part), we can't use the
+// existing codemap.
+//
+// Therefore, we must use the pretty printer (yuck) to turn the AST node into a
+// string, which we then re-tokenise (double yuck), but first we have to patch
+// the pretty-printed string on to the end of the existing codemap (infinity-yuck).
+fn tts_for_item(item: &Annotatable, parse_sess: &ParseSess) -> Vec<TokenTree> {
+    let text = match *item {
+        Annotatable::Item(ref i) => pprust::item_to_string(i),
+        Annotatable::TraitItem(ref ti) => pprust::trait_item_to_string(ti),
+        Annotatable::ImplItem(ref ii) => pprust::impl_item_to_string(ii),
+    };
+    string_to_tts(text, parse_sess)
+}
+
+fn tts_for_attr(attr: &ast::Attribute, parse_sess: &ParseSess) -> Vec<TokenTree> {
+    string_to_tts(pprust::attr_to_string(attr), parse_sess)
+}
+
+fn string_to_tts(text: String, parse_sess: &ParseSess) -> Vec<TokenTree> {
+    let filemap = parse_sess.codemap()
+                            .new_filemap(String::from("<macro expansion>"), None, text);
+
+    let lexer = lexer::StringReader::new(&parse_sess.span_diagnostic, filemap);
+    let mut parser = Parser::new(parse_sess, Vec::new(), Box::new(lexer));
+    panictry!(parser.parse_all_token_trees())
+}
+
 impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
     fn fold_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
         let mut expr = self.cfg.configure_expr(expr).unwrap();
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index da82c9ffab1..3746a51d359 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -49,22 +49,19 @@ impl<'a> ParserAnyMacro<'a> {
     /// allowed to be there.
     fn ensure_complete_parse(&self, allow_semi: bool, context: &str) {
         let mut parser = self.parser.borrow_mut();
-        if allow_semi && parser.token == token::Semi {
-            parser.bump();
-        }
-        if parser.token != token::Eof {
+        parser.ensure_complete_parse(allow_semi, |parser| {
             let token_str = parser.this_token_to_string();
             let msg = format!("macro expansion ignores token `{}` and any \
                                following",
                               token_str);
             let span = parser.span;
-            let mut err = parser.diagnostic().struct_span_err(span, &msg[..]);
+            let mut err = parser.diagnostic().struct_span_err(span, &msg);
             let msg = format!("caused by the macro expansion here; the usage \
                                of `{}!` is likely invalid in {} context",
                                self.macro_ident, context);
-            err.span_note(self.site_span, &msg[..])
+            err.span_note(self.site_span, &msg)
                .emit();
-        }
+        });
     }
 }
 
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 53294e78710..6c0e2425d37 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -110,7 +110,6 @@ impl<'a> Reader for StringReader<'a> {
             Some(t) => self.pos > t,
             None => false,
         }
-
     }
     /// Return the next token. EFFECT: advances the string_reader.
     fn try_next_token(&mut self) -> Result<TokenAndSpan, ()> {
@@ -222,28 +221,6 @@ impl<'a> StringReader<'a> {
         sr
     }
 
-    pub fn from_span<'b>(span_diagnostic: &'b Handler,
-                         span: Span,
-                         codemap: &CodeMap)
-                         -> StringReader<'b> {
-        let start_pos = codemap.lookup_byte_offset(span.lo);
-        let last_pos = codemap.lookup_byte_offset(span.hi);
-        assert!(start_pos.fm.name == last_pos.fm.name, "Attempt to lex span which crosses files");
-        let mut sr = StringReader::new_raw_internal(span_diagnostic, start_pos.fm.clone());
-        sr.pos = span.lo;
-        sr.last_pos = span.lo;
-        sr.terminator = Some(span.hi);
-        sr.save_new_lines = false;
-
-        sr.bump();
-
-        if let Err(_) = sr.advance_token() {
-            sr.emit_fatal_errors();
-            panic!(FatalError);
-        }
-        sr
-    }
-
     pub fn curr_is(&self, c: char) -> bool {
         self.curr == Some(c)
     }
diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index 4ad8e227cbb..5aa0efdec11 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -258,13 +258,6 @@ fn file_to_filemap(sess: &ParseSess, path: &Path, spanopt: Option<Span>)
     }
 }
 
-pub fn span_to_tts(sess: &ParseSess, span: Span) -> Vec<tokenstream::TokenTree> {
-    let cfg = Vec::new();
-    let srdr = lexer::StringReader::from_span(&sess.span_diagnostic, span, &sess.code_map);
-    let mut p1 = Parser::new(sess, cfg, Box::new(srdr));
-    panictry!(p1.parse_all_token_trees())
-}
-
 /// Given a filemap, produce a sequence of token-trees
 pub fn filemap_to_tts(sess: &ParseSess, filemap: Rc<FileMap>)
     -> Vec<tokenstream::TokenTree> {
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 5cd4a046577..23085fadc5e 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -3872,15 +3872,17 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_stmt_(&mut self, macro_expanded: bool) -> Option<Stmt> {
-        self.parse_stmt_without_recovery(macro_expanded).unwrap_or_else(|mut e| {
+    fn parse_stmt_(&mut self, macro_legacy_warnings: bool) -> Option<Stmt> {
+        self.parse_stmt_without_recovery(macro_legacy_warnings).unwrap_or_else(|mut e| {
             e.emit();
             self.recover_stmt_(SemiColonMode::Break);
             None
         })
     }
 
-    fn parse_stmt_without_recovery(&mut self, macro_expanded: bool) -> PResult<'a, Option<Stmt>> {
+    fn parse_stmt_without_recovery(&mut self,
+                                   macro_legacy_warnings: bool)
+                                   -> PResult<'a, Option<Stmt>> {
         maybe_whole!(Some deref self, NtStmt);
 
         let attrs = self.parse_outer_attributes()?;
@@ -3950,7 +3952,7 @@ impl<'a> Parser<'a> {
                 // We used to incorrectly stop parsing macro-expanded statements here.
                 // If the next token will be an error anyway but could have parsed with the
                 // earlier behavior, stop parsing here and emit a warning to avoid breakage.
-                else if macro_expanded && self.token.can_begin_expr() && match self.token {
+                else if macro_legacy_warnings && self.token.can_begin_expr() && match self.token {
                     // These can continue an expression, so we can't stop parsing and warn.
                     token::OpenDelim(token::Paren) | token::OpenDelim(token::Bracket) |
                     token::BinOp(token::Minus) | token::BinOp(token::Star) |
@@ -4125,8 +4127,8 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse a statement, including the trailing semicolon.
-    pub fn parse_full_stmt(&mut self, macro_expanded: bool) -> PResult<'a, Option<Stmt>> {
-        let mut stmt = match self.parse_stmt_(macro_expanded) {
+    pub fn parse_full_stmt(&mut self, macro_legacy_warnings: bool) -> PResult<'a, Option<Stmt>> {
+        let mut stmt = match self.parse_stmt_(macro_legacy_warnings) {
             Some(stmt) => stmt,
             None => return Ok(None),
         };
@@ -4146,7 +4148,7 @@ impl<'a> Parser<'a> {
             }
             StmtKind::Local(..) => {
                 // We used to incorrectly allow a macro-expanded let statement to lack a semicolon.
-                if macro_expanded && self.token != token::Semi {
+                if macro_legacy_warnings && self.token != token::Semi {
                     self.warn_missing_semicolon();
                 } else {
                     self.expect_one_of(&[token::Semi], &[])?;
@@ -6169,4 +6171,15 @@ impl<'a> Parser<'a> {
             _ =>  Err(self.fatal("expected string literal"))
         }
     }
+
+    pub fn ensure_complete_parse<F>(&mut self, allow_semi: bool, on_err: F)
+        where F: FnOnce(&Parser)
+    {
+        if allow_semi && self.token == token::Semi {
+            self.bump();
+        }
+        if self.token != token::Eof {
+            on_err(self);
+        }
+    }
 }
diff --git a/src/libsyntax_ext/deriving/custom.rs b/src/libsyntax_ext/deriving/custom.rs
index 465fc0016e5..624fabd1424 100644
--- a/src/libsyntax_ext/deriving/custom.rs
+++ b/src/libsyntax_ext/deriving/custom.rs
@@ -15,7 +15,7 @@ use rustc_macro::{TokenStream, __internal};
 use syntax::ast::{self, ItemKind};
 use syntax::codemap::{ExpnInfo, MacroAttribute, NameAndSpan, Span};
 use syntax::ext::base::*;
-use syntax::fold::{self, Folder};
+use syntax::fold::Folder;
 use syntax::parse::token::intern;
 use syntax::print::pprust;
 
@@ -97,14 +97,3 @@ impl MultiItemModifier for CustomDerive {
     }
 }
 
-struct ChangeSpan { span: Span }
-
-impl Folder for ChangeSpan {
-    fn new_span(&mut self, _sp: Span) -> Span {
-        self.span
-    }
-
-    fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
-        fold::noop_fold_mac(mac, self)
-    }
-}