rustc: move the formatter into ty::print::PrintCx.

src/librustc/lib.rs

@@ -31,6 +31,7 @@
 #![deny(rust_2018_idioms)]
 #![allow(explicit_outlives_requirements)]
 
+#![feature(arbitrary_self_types)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(core_intrinsics)]

src/librustc/mir/mod.rs

@@ -2369,7 +2369,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                 };
 
                 // When printing regions, add trailing space if necessary.
-                ty::print::PrintCx::with(|cx| {
+                ty::print::PrintCx::with(ty::print::FmtPrinter { fmt }, |cx| {
                     let region = if cx.is_verbose || cx.identify_regions {
                         let mut region = region.to_string();
                         if region.len() > 0 {
@@ -2380,7 +2380,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                         // Do not even print 'static
                         String::new()
                     };
-                    write!(fmt, "&{}{}{:?}", region, kind_str, place)
+                    write!(cx.printer.fmt, "&{}{}{:?}", region, kind_str, place)
                 })
             }
 

src/librustc/ty/item_path.rs

@@ -59,11 +59,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     /// root, unless with_forced_absolute_paths was used.
     pub fn item_path_str(self, def_id: DefId) -> String {
         debug!("item_path_str: def_id={:?}", def_id);
-        let mut cx = PrintCx::new(self);
         if FORCE_ABSOLUTE.with(|force| force.get()) {
-            AbsolutePathPrinter::print_item_path(&mut cx, def_id)
+            PrintCx::new(self, AbsolutePathPrinter).print_item_path(def_id)
         } else {
-            LocalPathPrinter::print_item_path(&mut cx, def_id)
+            PrintCx::new(self, LocalPathPrinter).print_item_path(def_id)
         }
     }
 
@@ -76,26 +75,23 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     /// suitable for user output. It always begins with a crate identifier.
     pub fn absolute_item_path_str(self, def_id: DefId) -> String {
         debug!("absolute_item_path_str: def_id={:?}", def_id);
-        let mut cx = PrintCx::new(self);
+        PrintCx::new(self, AbsolutePathPrinter).print_item_path(def_id)
-        AbsolutePathPrinter::print_item_path(&mut cx, def_id)
     }
 }
 
-impl PrintCx<'a, 'gcx, 'tcx> {
+impl<P: ItemPathPrinter> PrintCx<'a, 'gcx, 'tcx, P> {
-    pub fn default_print_item_path<P>(&mut self, def_id: DefId) -> P::Path
+    pub fn default_print_item_path(&mut self, def_id: DefId) -> P::Path {
-        where P: ItemPathPrinter
-    {
         debug!("default_print_item_path: def_id={:?}", def_id);
         let key = self.tcx.def_key(def_id);
         debug!("default_print_item_path: key={:?}", key);
         match key.disambiguated_data.data {
             DefPathData::CrateRoot => {
                 assert!(key.parent.is_none());
-                P::path_crate(self, def_id.krate)
+                self.path_crate(def_id.krate)
             }
 
             DefPathData::Impl => {
-                self.default_print_impl_path::<P>(def_id)
+                self.default_print_impl_path(def_id)
             }
 
             // Unclear if there is any value in distinguishing these.
@@ -121,20 +117,18 @@ impl PrintCx<'a, 'gcx, 'tcx> {
             data @ DefPathData::ImplTrait |
             data @ DefPathData::GlobalMetaData(..) => {
                 let parent_did = self.tcx.parent_def_id(def_id).unwrap();
-                let path = P::print_item_path(self, parent_did);
+                let path = self.print_item_path(parent_did);
-                P::path_append(path, &data.as_interned_str().as_symbol().as_str())
+                self.path_append(path, &data.as_interned_str().as_symbol().as_str())
             },
 
             DefPathData::StructCtor => { // present `X` instead of `X::{{constructor}}`
                 let parent_def_id = self.tcx.parent_def_id(def_id).unwrap();
-                P::print_item_path(self, parent_def_id)
+                self.print_item_path(parent_def_id)
             }
         }
     }
 
-    fn default_print_impl_path<P>(&mut self, impl_def_id: DefId) -> P::Path
+    fn default_print_impl_path(&mut self, impl_def_id: DefId) -> P::Path {
-        where P: ItemPathPrinter
-    {
         debug!("default_print_impl_path: impl_def_id={:?}", impl_def_id);
         let parent_def_id = self.tcx.parent_def_id(impl_def_id).unwrap();
 
@@ -147,7 +141,7 @@ impl PrintCx<'a, 'gcx, 'tcx> {
         };
 
         if !use_types {
-            return self.default_print_impl_path_fallback::<P>(impl_def_id);
+            return self.default_print_impl_path_fallback(impl_def_id);
         }
 
         // Decide whether to print the parent path for the impl.
@@ -171,11 +165,11 @@ impl PrintCx<'a, 'gcx, 'tcx> {
             // If the impl is not co-located with either self-type or
             // trait-type, then fallback to a format that identifies
             // the module more clearly.
-            let path = P::print_item_path(self, parent_def_id);
+            let path = self.print_item_path(parent_def_id);
             if let Some(trait_ref) = impl_trait_ref {
-                return P::path_append(path, &format!("<impl {} for {}>", trait_ref, self_ty));
+                return self.path_append(path, &format!("<impl {} for {}>", trait_ref, self_ty));
             } else {
-                return P::path_append(path, &format!("<impl {}>", self_ty));
+                return self.path_append(path, &format!("<impl {}>", self_ty));
             }
         }
 
@@ -184,7 +178,7 @@ impl PrintCx<'a, 'gcx, 'tcx> {
 
         if let Some(trait_ref) = impl_trait_ref {
             // Trait impls.
-            return P::path_impl(self, &format!("<{} as {}>", self_ty, trait_ref));
+            return self.path_impl(&format!("<{} as {}>", self_ty, trait_ref));
         }
 
         // Inherent impls. Try to print `Foo::bar` for an inherent
@@ -194,13 +188,13 @@ impl PrintCx<'a, 'gcx, 'tcx> {
             ty::Adt(adt_def, substs) => {
                 // FIXME(eddyb) always print without <> here.
                 if substs.types().next().is_none() { // ignore regions
-                    P::print_item_path(self, adt_def.did)
+                    self.print_item_path(adt_def.did)
                 } else {
-                    P::path_impl(self, &format!("<{}>", self_ty))
+                    self.path_impl(&format!("<{}>", self_ty))
                 }
             }
 
-            ty::Foreign(did) => P::print_item_path(self, did),
+            ty::Foreign(did) => self.print_item_path(did),
 
             ty::Bool |
             ty::Char |
@@ -208,28 +202,26 @@ impl PrintCx<'a, 'gcx, 'tcx> {
             ty::Uint(_) |
             ty::Float(_) |
             ty::Str => {
-                P::path_impl(self, &self_ty.to_string())
+                self.path_impl(&self_ty.to_string())
             }
 
             _ => {
-                P::path_impl(self, &format!("<{}>", self_ty))
+                self.path_impl(&format!("<{}>", self_ty))
             }
         }
     }
 
-    fn default_print_impl_path_fallback<P>(&mut self, impl_def_id: DefId) -> P::Path
+    fn default_print_impl_path_fallback(&mut self, impl_def_id: DefId) -> P::Path {
-        where P: ItemPathPrinter
-    {
         // If no type info is available, fall back to
         // pretty printing some span information. This should
         // only occur very early in the compiler pipeline.
         // FIXME(eddyb) this should just be using `tcx.def_span(impl_def_id)`
         let parent_def_id = self.tcx.parent_def_id(impl_def_id).unwrap();
-        let path = P::print_item_path(self, parent_def_id);
+        let path = self.print_item_path(parent_def_id);
         let hir_id = self.tcx.hir().as_local_hir_id(impl_def_id).unwrap();
         let item = self.tcx.hir().expect_item_by_hir_id(hir_id);
         let span_str = self.tcx.sess.source_map().span_to_string(item.span);
-        P::path_append(path, &format!("<impl at {}>", span_str))
+        self.path_append(path, &format!("<impl at {}>", span_str))
     }
 }
 
@@ -296,13 +288,17 @@ pub fn characteristic_def_id_of_type(ty: Ty<'_>) -> Option<DefId> {
 pub trait ItemPathPrinter: Sized {
     type Path;
 
-    fn print_item_path(cx: &mut PrintCx<'_, '_, '_>, def_id: DefId) -> Self::Path {
+    fn print_item_path(self: &mut PrintCx<'_, '_, '_, Self>, def_id: DefId) -> Self::Path {
-        cx.default_print_item_path::<Self>(def_id)
+        self.default_print_item_path(def_id)
     }
 
-    fn path_crate(cx: &mut PrintCx<'_, '_, '_>, cnum: CrateNum) -> Self::Path;
+    fn path_crate(self: &mut PrintCx<'_, '_, '_, Self>, cnum: CrateNum) -> Self::Path;
-    fn path_impl(cx: &mut PrintCx<'_, '_, '_>, text: &str) -> Self::Path;
+    fn path_impl(self: &mut PrintCx<'_, '_, '_, Self>, text: &str) -> Self::Path;
-    fn path_append(path: Self::Path, text: &str) -> Self::Path;
+    fn path_append(
+        self: &mut PrintCx<'_, '_, '_, Self>,
+        path: Self::Path,
+        text: &str,
+    ) -> Self::Path;
 }
 
 struct AbsolutePathPrinter;
@@ -310,13 +306,17 @@ struct AbsolutePathPrinter;
 impl ItemPathPrinter for AbsolutePathPrinter {
     type Path = String;
 
-    fn path_crate(cx: &mut PrintCx<'_, '_, '_>, cnum: CrateNum) -> Self::Path {
+    fn path_crate(self: &mut PrintCx<'_, '_, '_, Self>, cnum: CrateNum) -> Self::Path {
-        cx.tcx.original_crate_name(cnum).to_string()
+        self.tcx.original_crate_name(cnum).to_string()
     }
-    fn path_impl(_cx: &mut PrintCx<'_, '_, '_>, text: &str) -> Self::Path {
+    fn path_impl(self: &mut PrintCx<'_, '_, '_, Self>, text: &str) -> Self::Path {
         text.to_string()
     }
-    fn path_append(mut path: Self::Path, text: &str) -> Self::Path {
+    fn path_append(
+        self: &mut PrintCx<'_, '_, '_, Self>,
+        mut path: Self::Path,
+        text: &str,
+    ) -> Self::Path {
         if !path.is_empty() {
             path.push_str("::");
         }
@@ -332,7 +332,7 @@ impl LocalPathPrinter {
     /// from at least one local module and returns true. If the crate defining `def_id` is
     /// declared with an `extern crate`, the path is guaranteed to use the `extern crate`.
     fn try_print_visible_item_path(
-        cx: &mut PrintCx<'_, '_, '_>,
+        self: &mut PrintCx<'_, '_, '_, Self>,
         def_id: DefId,
     ) -> Option<<Self as ItemPathPrinter>::Path> {
         debug!("try_print_visible_item_path: def_id={:?}", def_id);
@@ -343,7 +343,7 @@ impl LocalPathPrinter {
             let cnum = def_id.krate;
 
             if cnum == LOCAL_CRATE {
-                return Some(Self::path_crate(cx, cnum));
+                return Some(self.path_crate(cnum));
             }
 
             // In local mode, when we encounter a crate other than
@@ -356,7 +356,7 @@ impl LocalPathPrinter {
             // 2. for an extern inferred from a path or an indirect crate,
             //    where there is no explicit `extern crate`, we just prepend
             //    the crate name.
-            match *cx.tcx.extern_crate(def_id) {
+            match *self.tcx.extern_crate(def_id) {
                 Some(ExternCrate {
                     src: ExternCrateSource::Extern(def_id),
                     direct: true,
@@ -365,14 +365,14 @@ impl LocalPathPrinter {
                 }) => {
                     debug!("try_print_visible_item_path: def_id={:?}", def_id);
                     let path = if !span.is_dummy() {
-                        Self::print_item_path(cx, def_id)
+                        self.print_item_path(def_id)
                     } else {
-                        Self::path_crate(cx, cnum)
+                        self.path_crate(cnum)
                     };
                     return Some(path);
                 }
                 None => {
-                    return Some(Self::path_crate(cx, cnum));
+                    return Some(self.path_crate(cnum));
                 }
                 _ => {},
             }
@@ -382,9 +382,9 @@ impl LocalPathPrinter {
             return None;
         }
 
-        let visible_parent_map = cx.tcx.visible_parent_map(LOCAL_CRATE);
+        let visible_parent_map = self.tcx.visible_parent_map(LOCAL_CRATE);
 
-        let mut cur_def_key = cx.tcx.def_key(def_id);
+        let mut cur_def_key = self.tcx.def_key(def_id);
         debug!("try_print_visible_item_path: cur_def_key={:?}", cur_def_key);
 
         // For a UnitStruct or TupleStruct we want the name of its parent rather than <unnamed>.
@@ -394,12 +394,12 @@ impl LocalPathPrinter {
                 index: cur_def_key.parent.expect("DefPathData::StructCtor missing a parent"),
             };
 
-            cur_def_key = cx.tcx.def_key(parent);
+            cur_def_key = self.tcx.def_key(parent);
         }
 
         let visible_parent = visible_parent_map.get(&def_id).cloned()?;
-        let path = Self::try_print_visible_item_path(cx, visible_parent)?;
+        let path = self.try_print_visible_item_path(visible_parent)?;
-        let actual_parent = cx.tcx.parent(def_id);
+        let actual_parent = self.tcx.parent(def_id);
 
         let data = cur_def_key.disambiguated_data.data;
         debug!(
@@ -441,7 +441,7 @@ impl LocalPathPrinter {
             // have access to the re-exported name.
             DefPathData::Module(actual_name) |
             DefPathData::TypeNs(actual_name) if Some(visible_parent) != actual_parent => {
-                cx.tcx.item_children(visible_parent)
+                self.tcx.item_children(visible_parent)
                     .iter()
                     .find(|child| child.def.def_id() == def_id)
                     .map(|child| child.ident.as_str())
@@ -451,7 +451,7 @@ impl LocalPathPrinter {
                 data.get_opt_name().map(|n| n.as_str()).unwrap_or_else(|| {
                     // Re-exported `extern crate` (#43189).
                     if let DefPathData::CrateRoot = data {
-                        cx.tcx.original_crate_name(def_id.krate).as_str()
+                        self.tcx.original_crate_name(def_id.krate).as_str()
                     } else {
                         Symbol::intern("<unnamed>").as_str()
                     }
@@ -459,21 +459,21 @@ impl LocalPathPrinter {
             },
         };
         debug!("try_print_visible_item_path: symbol={:?}", symbol);
-        Some(Self::path_append(path, &symbol))
+        Some(self.path_append(path, &symbol))
     }
 }
 
 impl ItemPathPrinter for LocalPathPrinter {
     type Path = String;
 
-    fn print_item_path(cx: &mut PrintCx<'_, '_, '_>, def_id: DefId) -> Self::Path {
+    fn print_item_path(self: &mut PrintCx<'_, '_, '_, Self>, def_id: DefId) -> Self::Path {
-        Self::try_print_visible_item_path(cx, def_id)
+        self.try_print_visible_item_path(def_id)
-            .unwrap_or_else(|| cx.default_print_item_path::<Self>(def_id))
+            .unwrap_or_else(|| self.default_print_item_path(def_id))
     }
 
-    fn path_crate(cx: &mut PrintCx<'_, '_, '_>, cnum: CrateNum) -> Self::Path {
+    fn path_crate(self: &mut PrintCx<'_, '_, '_, Self>, cnum: CrateNum) -> Self::Path {
         if cnum == LOCAL_CRATE {
-            if cx.tcx.sess.rust_2018() {
+            if self.tcx.sess.rust_2018() {
                 // We add the `crate::` keyword on Rust 2018, only when desired.
                 if SHOULD_PREFIX_WITH_CRATE.with(|flag| flag.get()) {
                     return keywords::Crate.name().to_string();
@@ -481,13 +481,17 @@ impl ItemPathPrinter for LocalPathPrinter {
             }
             String::new()
         } else {
-            cx.tcx.crate_name(cnum).to_string()
+            self.tcx.crate_name(cnum).to_string()
         }
     }
-    fn path_impl(_cx: &mut PrintCx<'_, '_, '_>, text: &str) -> Self::Path {
+    fn path_impl(self: &mut PrintCx<'_, '_, '_, Self>, text: &str) -> Self::Path {
         text.to_string()
     }
-    fn path_append(mut path: Self::Path, text: &str) -> Self::Path {
+    fn path_append(
+        self: &mut PrintCx<'_, '_, '_, Self>,
+        mut path: Self::Path,
+        text: &str,
+    ) -> Self::Path {
         if !path.is_empty() {
             path.push_str("::");
         }

src/librustc/ty/print.rs

@@ -4,6 +4,7 @@ use rustc_data_structures::fx::FxHashSet;
 use syntax::symbol::InternedString;
 
 use std::fmt;
+use std::ops::Deref;
 
 // FIXME(eddyb) this module uses `pub(crate)` for things used only
 // from `ppaux` - when that is removed, they can be re-privatized.
@@ -21,8 +22,9 @@ impl<'tcx> ty::fold::TypeVisitor<'tcx> for LateBoundRegionNameCollector {
     }
 }
 
-pub struct PrintCx<'a, 'gcx, 'tcx> {
+pub struct PrintCx<'a, 'gcx, 'tcx, P> {
     pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
+    pub printer: P,
     pub(crate) is_debug: bool,
     pub(crate) is_verbose: bool,
     pub(crate) identify_regions: bool,
@@ -31,10 +33,20 @@ pub struct PrintCx<'a, 'gcx, 'tcx> {
     pub(crate) binder_depth: usize,
 }
 
-impl PrintCx<'a, 'gcx, 'tcx> {
+// HACK(eddyb) this is solely for `self: &mut PrintCx<Self>`, e.g. to
-    pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
+// implement traits on the printer and call the methods on the context.
+impl<P> Deref for PrintCx<'_, '_, '_, P> {
+    type Target = P;
+    fn deref(&self) -> &P {
+        &self.printer
+    }
+}
+
+impl<P> PrintCx<'a, 'gcx, 'tcx, P> {
+    pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>, printer: P) -> Self {
         PrintCx {
             tcx,
+            printer,
             is_debug: false,
             is_verbose: tcx.sess.verbose(),
             identify_regions: tcx.sess.opts.debugging_opts.identify_regions,
@@ -44,8 +56,8 @@ impl PrintCx<'a, 'gcx, 'tcx> {
         }
     }
 
-    pub(crate) fn with<R>(f: impl FnOnce(PrintCx<'_, '_, '_>) -> R) -> R {
+    pub(crate) fn with<R>(printer: P, f: impl FnOnce(PrintCx<'_, '_, '_, P>) -> R) -> R {
-        ty::tls::with(|tcx| f(PrintCx::new(tcx)))
+        ty::tls::with(|tcx| f(PrintCx::new(tcx, printer)))
     }
     pub(crate) fn prepare_late_bound_region_info<T>(&mut self, value: &ty::Binder<T>)
     where T: TypeFoldable<'tcx>
@@ -57,24 +69,26 @@ impl PrintCx<'a, 'gcx, 'tcx> {
     }
 }
 
-pub trait Print<'tcx> {
+pub trait Print<'tcx, P> {
-    fn print<F: fmt::Write>(&self, f: &mut F, cx: &mut PrintCx<'_, '_, 'tcx>) -> fmt::Result;
+    type Output;
-    fn print_display<F: fmt::Write>(
+
-        &self,
+    fn print(&self, cx: &mut PrintCx<'_, '_, 'tcx, P>) -> Self::Output;
-        f: &mut F,
+    fn print_display(&self, cx: &mut PrintCx<'_, '_, 'tcx, P>) -> Self::Output {
-        cx: &mut PrintCx<'_, '_, 'tcx>,
-    ) -> fmt::Result {
         let old_debug = cx.is_debug;
         cx.is_debug = false;
-        let result = self.print(f, cx);
+        let result = self.print(cx);
         cx.is_debug = old_debug;
         result
     }
-    fn print_debug<F: fmt::Write>(&self, f: &mut F, cx: &mut PrintCx<'_, '_, 'tcx>) -> fmt::Result {
+    fn print_debug(&self, cx: &mut PrintCx<'_, '_, 'tcx, P>) -> Self::Output {
         let old_debug = cx.is_debug;
         cx.is_debug = true;
-        let result = self.print(f, cx);
+        let result = self.print(cx);
         cx.is_debug = old_debug;
         result
     }
 }
+
+pub struct FmtPrinter<F: fmt::Write> {
+    pub fmt: F,
+}

src/librustc_codegen_utils/lib.rs

@@ -4,6 +4,7 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 
+#![feature(arbitrary_self_types)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(custom_attribute)]

src/librustc_codegen_utils/symbol_names.rs

@@ -225,8 +225,7 @@ fn get_symbol_hash<'a, 'tcx>(
 
 fn def_symbol_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> ty::SymbolName {
     item_path::with_forced_absolute_paths(|| {
-        let mut cx = PrintCx::new(tcx);
+        PrintCx::new(tcx, SymbolPathPrinter).print_item_path(def_id).into_interned()
-        SymbolPathPrinter::print_item_path(&mut cx, def_id).into_interned()
     })
 }
 
@@ -401,17 +400,21 @@ struct SymbolPathPrinter;
 impl ItemPathPrinter for SymbolPathPrinter {
     type Path = SymbolPath;
 
-    fn path_crate(cx: &mut PrintCx<'_, '_, '_>, cnum: CrateNum) -> Self::Path {
+    fn path_crate(self: &mut PrintCx<'_, '_, '_, Self>, cnum: CrateNum) -> Self::Path {
-        let mut path = SymbolPath::new(cx.tcx);
+        let mut path = SymbolPath::new(self.tcx);
-        path.push(&cx.tcx.original_crate_name(cnum).as_str());
+        path.push(&self.tcx.original_crate_name(cnum).as_str());
         path
     }
-    fn path_impl(cx: &mut PrintCx<'_, '_, '_>, text: &str) -> Self::Path {
+    fn path_impl(self: &mut PrintCx<'_, '_, '_, Self>, text: &str) -> Self::Path {
-        let mut path = SymbolPath::new(cx.tcx);
+        let mut path = SymbolPath::new(self.tcx);
         path.push(text);
         path
     }
-    fn path_append(mut path: Self::Path, text: &str) -> Self::Path {
+    fn path_append(
+        self: &mut PrintCx<'_, '_, '_, Self>,
+        mut path: Self::Path,
+        text: &str,
+    ) -> Self::Path {
         path.push(text);
         path
     }

src/librustdoc/clean/mod.rs

@@ -4233,20 +4233,23 @@ where F: Fn(DefId) -> Def {
     impl ItemPathPrinter for AbsolutePathPrinter {
         type Path = Vec<String>;
 
-        fn path_crate(cx: &mut PrintCx<'_, '_, '_>, cnum: CrateNum) -> Self::Path {
+        fn path_crate(self: &mut PrintCx<'_, '_, '_, Self>, cnum: CrateNum) -> Self::Path {
-            vec![cx.tcx.original_crate_name(cnum).to_string()]
+            vec![self.tcx.original_crate_name(cnum).to_string()]
         }
-        fn path_impl(_: &mut PrintCx<'_, '_, '_>, text: &str) -> Self::Path {
+        fn path_impl(self: &mut PrintCx<'_, '_, '_, Self>, text: &str) -> Self::Path {
             vec![text.to_string()]
         }
-        fn path_append(mut path: Self::Path, text: &str) -> Self::Path {
+        fn path_append(
+            self: &mut PrintCx<'_, '_, '_, Self>,
+            mut path: Self::Path,
+            text: &str,
+        ) -> Self::Path {
             path.push(text.to_string());
             path
         }
     }
 
-    let mut cx = PrintCx::new(tcx);
+    let names = PrintCx::new(tcx, AbsolutePathPrinter).print_item_path(def_id);
-    let names = AbsolutePathPrinter::print_item_path(&mut cx, def_id);
 
     hir::Path {
         span: DUMMY_SP,

src/librustdoc/lib.rs

@@ -5,6 +5,7 @@
 
 #![feature(bind_by_move_pattern_guards)]
 #![feature(rustc_private)]
+#![feature(arbitrary_self_types)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(nll)]