auto merge of #13559 : FlaPer87/rust/remove-special-root, r=nikomatsakis

This patch removes the special auto-rooting for `@` from the borrow checker. With `@` moving into a library, it doesn't make sense to keep this code around anymore. It also simplifies `trans` by removing root checking from there 

@nikomatsakis

Closes: #11586

Author: bors

src/libfourcc/lib.rs

@@ -91,7 +91,7 @@ pub fn expand_syntax_ext(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]) ->
 
     let s = match expr.node {
         // expression is a literal
-        ast::ExprLit(lit) => match lit.node {
+        ast::ExprLit(ref lit) => match lit.node {
             // string literal
             ast::LitStr(ref s, _) => {
                 if s.get().char_len() != 4 {

src/librustc/driver/driver.rs

@@ -346,8 +346,7 @@ pub fn phase_3_run_analysis_passes(sess: Session,
     time(time_passes, "effect checking", (), |_|
          middle::effect::check_crate(&ty_cx, krate));
 
-    let middle::moves::MoveMaps {moves_map, moved_variables_set,
-                                 capture_map} =
+    let middle::moves::MoveMaps {moves_map, capture_map} =
         time(time_passes, "compute moves", (), |_|
              middle::moves::compute_moves(&ty_cx, krate));
 
@@ -357,14 +356,11 @@ pub fn phase_3_run_analysis_passes(sess: Session,
     time(time_passes, "liveness checking", (), |_|
          middle::liveness::check_crate(&ty_cx, &capture_map, krate));
 
-    let root_map =
-        time(time_passes, "borrow checking", (), |_|
-             middle::borrowck::check_crate(&ty_cx, &moves_map,
-                                           &moved_variables_set,
-                                           &capture_map, krate));
+    time(time_passes, "borrow checking", (), |_|
+         middle::borrowck::check_crate(&ty_cx, &moves_map,
+                                       &capture_map, krate));
 
     drop(moves_map);
-    drop(moved_variables_set);
 
     time(time_passes, "kind checking", (), |_|
          kind::check_crate(&ty_cx, krate));
@@ -389,7 +385,6 @@ pub fn phase_3_run_analysis_passes(sess: Session,
         exported_items: exported_items,
         public_items: public_items,
         maps: astencode::Maps {
-            root_map: root_map,
             capture_map: RefCell::new(capture_map)
         },
         reachable: reachable_map

src/librustc/middle/astencode.rs

@@ -54,7 +54,6 @@ use writer = serialize::ebml::writer;
 
 // Auxiliary maps of things to be encoded
 pub struct Maps {
-    pub root_map: middle::borrowck::root_map,
     pub capture_map: RefCell<middle::moves::CaptureMap>,
 }
 

src/librustc/middle/borrowck/gather_loans/lifetime.rs

@@ -65,9 +65,6 @@ struct GuaranteeLifetimeContext<'a> {
 }
 
 impl<'a> GuaranteeLifetimeContext<'a> {
-    fn tcx(&self) -> &'a ty::ctxt {
-        self.bccx.tcx
-    }
 
     fn check(&self, cmt: &mc::cmt, discr_scope: Option<ast::NodeId>) -> R {
         //! Main routine. Walks down `cmt` until we find the "guarantor".
@@ -90,29 +87,10 @@ impl<'a> GuaranteeLifetimeContext<'a> {
                 Ok(())
             }
 
-            mc::cat_deref(ref base, derefs, mc::GcPtr) => {
-                let base_scope = self.scope(base);
-
-                // L-Deref-Managed-Imm-User-Root
-                let omit_root =
-                    self.bccx.is_subregion_of(self.loan_region, base_scope) &&
-                    self.is_rvalue_or_immutable(base) &&
-                    !self.is_moved(base);
-
-                if !omit_root {
-                    // L-Deref-Managed-Imm-Compiler-Root
-                    // L-Deref-Managed-Mut-Compiler-Root
-                    self.check_root(cmt, base, derefs, discr_scope)
-                } else {
-                    debug!("omitting root, base={}, base_scope={:?}",
-                           base.repr(self.tcx()), base_scope);
-                    Ok(())
-                }
-            }
-
             mc::cat_downcast(ref base) |
             mc::cat_deref(ref base, _, mc::OwnedPtr) |     // L-Deref-Send
-            mc::cat_interior(ref base, _) => {             // L-Field
+            mc::cat_interior(ref base, _) |                // L-Field
+            mc::cat_deref(ref base, _, mc::GcPtr) => {
                 self.check(base, discr_scope)
             }
 
@@ -174,74 +152,6 @@ impl<'a> GuaranteeLifetimeContext<'a> {
         }
     }
 
-    fn is_rvalue_or_immutable(&self,
-                              cmt: &mc::cmt) -> bool {
-        //! We can omit the root on an `@T` value if the location
-        //! that holds the box is either (1) an rvalue, in which case
-        //! it is in a non-user-accessible temporary, or (2) an immutable
-        //! lvalue.
-
-        cmt.mutbl.is_immutable() || match cmt.guarantor().cat {
-            mc::cat_rvalue(..) => true,
-            _ => false
-        }
-    }
-
-    fn check_root(&self,
-                  cmt_deref: &mc::cmt,
-                  cmt_base: &mc::cmt,
-                  derefs: uint,
-                  discr_scope: Option<ast::NodeId>) -> R {
-        debug!("check_root(cmt_deref={}, cmt_base={}, derefs={:?}, \
-                discr_scope={:?})",
-               cmt_deref.repr(self.tcx()),
-               cmt_base.repr(self.tcx()),
-               derefs,
-               discr_scope);
-
-        // Make sure that the loan does not exceed the maximum time
-        // that we can root the value, dynamically.
-        let root_region = ty::ReScope(self.root_scope_id);
-        if !self.bccx.is_subregion_of(self.loan_region, root_region) {
-            return Err(self.report_error(
-                err_out_of_root_scope(root_region, self.loan_region)));
-        }
-
-        // Extract the scope id that indicates how long the rooting is required
-        let root_scope = match self.loan_region {
-            ty::ReScope(id) => id,
-            _ => {
-                // the check above should fail for anything is not ReScope
-                self.bccx.tcx.sess.span_bug(
-                    cmt_base.span,
-                    format!("cannot issue root for scope region: {:?}",
-                         self.loan_region));
-            }
-        };
-
-        // If inside of a match arm, expand the rooting to the entire
-        // match. See the detailed discussion in `check()` above.
-        let root_scope = match discr_scope {
-            None => root_scope,
-            Some(id) => {
-                if self.bccx.is_subscope_of(root_scope, id) {
-                    id
-                } else {
-                    root_scope
-                }
-            }
-        };
-
-        // Add a record of what is required
-        let rm_key = root_map_key {id: cmt_deref.id, derefs: derefs};
-        let root_info = RootInfo {scope: root_scope};
-
-        self.bccx.root_map.borrow_mut().insert(rm_key, root_info);
-
-        debug!("root_key: {:?} root_info: {:?}", rm_key, root_info);
-        Ok(())
-    }
-
     fn check_scope(&self, max_scope: ty::Region) -> R {
         //! Reports an error if `loan_region` is larger than `valid_scope`
 
@@ -252,32 +162,6 @@ impl<'a> GuaranteeLifetimeContext<'a> {
         }
     }
 
-    fn is_moved(&self, cmt: &mc::cmt) -> bool {
-        //! True if `cmt` is something that is potentially moved
-        //! out of the current stack frame.
-
-        match cmt.guarantor().cat {
-            mc::cat_local(id) |
-            mc::cat_arg(id) => {
-                self.bccx.moved_variables_set.contains(&id)
-            }
-            mc::cat_rvalue(..) |
-            mc::cat_static_item |
-            mc::cat_copied_upvar(..) |
-            mc::cat_deref(..) |
-            mc::cat_upvar(..) => {
-                false
-            }
-            ref r @ mc::cat_downcast(..) |
-            ref r @ mc::cat_interior(..) |
-            ref r @ mc::cat_discr(..) => {
-                self.tcx().sess.span_bug(
-                    cmt.span,
-                    format!("illegal guarantor category: {:?}", r));
-            }
-        }
-    }
-
     fn scope(&self, cmt: &mc::cmt) -> ty::Region {
         //! Returns the maximal region scope for the which the
         //! lvalue `cmt` is guaranteed to be valid without any

src/librustc/middle/borrowck/gather_loans/restrictions.rs

@@ -101,12 +101,18 @@ impl<'a> RestrictionsContext<'a> {
                 self.extend(result, cmt.mutbl, LpInterior(i), restrictions)
             }
 
-            mc::cat_deref(cmt_base, _, pk @ mc::OwnedPtr) => {
+            mc::cat_deref(cmt_base, _, pk @ mc::OwnedPtr) |
+            mc::cat_deref(cmt_base, _, pk @ mc::GcPtr) => {
                 // R-Deref-Send-Pointer
                 //
                 // When we borrow the interior of an owned pointer, we
                 // cannot permit the base to be mutated, because that
                 // would cause the unique pointer to be freed.
+                //
+                // For a managed pointer, the rules are basically the
+                // same, because this could be the last ref.
+                // Eventually we should make these non-special and
+                // just rely on Deref<T> implementation.
                 let result = self.restrict(
                     cmt_base,
                     restrictions | RESTR_MUTATE);
@@ -134,11 +140,6 @@ impl<'a> RestrictionsContext<'a> {
                 Safe
             }
 
-            mc::cat_deref(_, _, mc::GcPtr) => {
-                // R-Deref-Imm-Managed
-                Safe
-            }
-
             mc::cat_deref(cmt_base, _, pk @ mc::BorrowedPtr(ty::MutBorrow, lt)) => {
                 // R-Deref-Mut-Borrowed
                 if !self.bccx.is_subregion_of(self.loan_region, lt) {