Ensure dataflow of a proc never looks at blocks from closed-over context.

Details: in a program like:
```
type T = proc(int) -> int; /* 4 */

pub fn outer(captured /* pat 16 */: T) -> T {
    (proc(x /* pat 23 */) {
        ((captured /* 29 */).foo((x /* 30 */)) /* 28 */)
    } /* block 27 */ /* 20 */)
} /* block 19 */ /* 12 */
```
the `captured` arg is moved from the outer fn into the inner proc (id=20).

The old dataflow analysis for flowed_move_data_moves, when looking at
the inner proc, would attempt to add a kill bit for `captured` at the
end of its scope; the problem is that it thought the end of the
`captured` arg's scope was the outer fn (id=12), even though at that
point in the analysis, the `captured` arg's scope should now be
restricted to the proc itself (id=20).

This patch fixes handling of upvars so that dataflow of a fn/proc
should never attempts to add a gen or kill bit to any NodeId outside
of the current fn/proc.  It accomplishes this by adding an `LpUpvar`
variant to `borrowck::LoanPath`, so for cases like `captured` above
will carry both their original `var_id`, as before, as well as the
`NodeId` for the closure that is capturing them.

As a drive-by fix to another occurrence of a similar bug that
nikomatsakis pointed out to me earlier, this also fixes
`gather_loans::compute_kill_scope` so that it computes the kill scope
of the `captured` arg to be block 27; that is, the block for the proc
itself (id=20).

(This is an updated version that generalizes the new loan path variant
to cover all upvars, and thus renamed the variant from `LpCopiedUpvar`
to just `LpUpvar`.)

Author: pnkfelix

src/librustc/middle/borrowck/check_loans.rs

@@ -242,7 +242,7 @@ impl<'a> CheckLoanCtxt<'a> {
         let mut loan_path = loan_path;
         loop {
             match *loan_path {
-                LpVar(_) => {
+                LpVar(_) | LpUpvar(_) => {
                     break;
                 }
                 LpExtend(ref lp_base, _, _) => {
@@ -632,7 +632,7 @@ impl<'a> CheckLoanCtxt<'a> {
          */
 
         match **lp {
-            LpVar(_) => {
+            LpVar(_) | LpUpvar(_) => {
                 // assigning to `x` does not require that `x` is initialized
             }
             LpExtend(ref lp_base, _, LpInterior(_)) => {

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

@@ -395,7 +395,8 @@ impl<'a> GatherLoanCtxt<'a> {
         //! from a local variable, mark the mutability decl as necessary.
 
         match *loan_path {
-            LpVar(local_id) => {
+            LpVar(local_id) |
+            LpUpvar(ty::UpvarId{ var_id: local_id, closure_expr_id: _ }) => {
                 self.tcx().used_mut_nodes.borrow_mut().insert(local_id);
             }
             LpExtend(ref base, mc::McInherited, _) => {
@@ -445,8 +446,8 @@ impl<'a> GatherLoanCtxt<'a> {
         //! with immutable `&` pointers, because borrows of such pointers
         //! do not require restrictions and hence do not cause a loan.
 
+        let lexical_scope = lp.kill_scope(self.bccx.tcx);
         let rm = &self.bccx.tcx.region_maps;
-        let lexical_scope = rm.var_scope(lp.node_id());
         if rm.is_subscope_of(lexical_scope, loan_scope) {
             lexical_scope
         } else {

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

@@ -67,13 +67,23 @@ impl<'a> RestrictionsContext<'a> {
             }
 
             mc::cat_local(local_id) |
-            mc::cat_arg(local_id) |
-            mc::cat_upvar(ty::UpvarId {var_id: local_id, ..}, _) => {
-                // R-Variable
+            mc::cat_arg(local_id) => {
+                // R-Variable, locally declared
                 let lp = Rc::new(LpVar(local_id));
                 SafeIf(lp.clone(), vec!(lp))
             }
 
+            mc::cat_upvar(upvar_id, _) => {
+                // R-Variable, captured into closure
+                let lp = Rc::new(LpUpvar(upvar_id));
+                SafeIf(lp.clone(), vec!(lp))
+            }
+
+            mc::cat_copied_upvar(..) => {
+                // FIXME(#2152) allow mutation of upvars
+                Safe
+            }
+
             mc::cat_downcast(cmt_base) => {
                 // When we borrow the interior of an enum, we have to
                 // ensure the enum itself is not mutated, because that
@@ -107,7 +117,6 @@ impl<'a> RestrictionsContext<'a> {
                 self.extend(result, cmt.mutbl, LpDeref(pk))
             }
 
-            mc::cat_copied_upvar(..) | // FIXME(#2152) allow mutation of upvars
             mc::cat_static_item(..) => {
                 Safe
             }

src/librustc/middle/borrowck/mod.rs

@@ -201,6 +201,7 @@ pub struct Loan {
 #[deriving(PartialEq, Eq, Hash)]
 pub enum LoanPath {
     LpVar(ast::NodeId),               // `x` in doc.rs
+    LpUpvar(ty::UpvarId),             // `x` captured by-value into closure
     LpExtend(Rc<LoanPath>, mc::MutabilityCategory, LoanPathElem)
 }
 
@@ -210,11 +211,25 @@ pub enum LoanPathElem {
     LpInterior(mc::InteriorKind) // `LV.f` in doc.rs
 }
 
+pub fn closure_to_block(closure_id: ast::NodeId,
+                    tcx: &ty::ctxt) -> ast::NodeId {
+    match tcx.map.get(closure_id) {
+        ast_map::NodeExpr(expr) => match expr.node {
+            ast::ExprProc(_decl, block) |
+            ast::ExprFnBlock(_decl, block) => { block.id }
+            _ => fail!("encountered non-closure id: {}", closure_id)
+        },
+        _ => fail!("encountered non-expr id: {}", closure_id)
+    }
+}
+
 impl LoanPath {
-    pub fn node_id(&self) -> ast::NodeId {
+    pub fn kill_scope(&self, tcx: &ty::ctxt) -> ast::NodeId {
         match *self {
-            LpVar(local_id) => local_id,
-            LpExtend(ref base, _, _) => base.node_id()
+            LpVar(local_id) => tcx.region_maps.var_scope(local_id),
+            LpUpvar(upvar_id) =>
+                closure_to_block(upvar_id.closure_expr_id, tcx),
+            LpExtend(ref base, _, _) => base.kill_scope(tcx),
         }
     }
 }
@@ -234,12 +249,18 @@ pub fn opt_loan_path(cmt: &mc::cmt) -> Option<Rc<LoanPath>> {
         }
 
         mc::cat_local(id) |
-        mc::cat_arg(id) |
-        mc::cat_copied_upvar(mc::CopiedUpvar { upvar_id: id, .. }) |
-        mc::cat_upvar(ty::UpvarId {var_id: id, ..}, _) => {
+        mc::cat_arg(id) => {
             Some(Rc::new(LpVar(id)))
         }
 
+        mc::cat_upvar(ty::UpvarId {var_id: id, closure_expr_id: proc_id}, _) |
+        mc::cat_copied_upvar(mc::CopiedUpvar { upvar_id: id,
+                                               onceness: _,
+                                               capturing_proc: proc_id }) => {
+            let upvar_id = ty::UpvarId{ var_id: id, closure_expr_id: proc_id };
+            Some(Rc::new(LpUpvar(upvar_id)))
+        }
+
         mc::cat_deref(ref cmt_base, _, pk) => {
             opt_loan_path(cmt_base).map(|lp| {
                 Rc::new(LpExtend(lp, cmt.mutbl, LpDeref(pk)))
@@ -693,6 +714,7 @@ impl<'a> BorrowckCtxt<'a> {
                                    loan_path: &LoanPath,
                                    out: &mut String) {
         match *loan_path {
+            LpUpvar(ty::UpvarId{ var_id: id, closure_expr_id: _ }) |
             LpVar(id) => {
                 out.push_str(ty::local_var_name_str(self.tcx, id).get());
             }
@@ -734,7 +756,7 @@ impl<'a> BorrowckCtxt<'a> {
                 self.append_autoderefd_loan_path_to_str(&**lp_base, out)
             }
 
-            LpVar(..) | LpExtend(_, _, LpInterior(..)) => {
+            LpVar(..) | LpUpvar(..) | LpExtend(_, _, LpInterior(..)) => {
                 self.append_loan_path_to_str(loan_path, out)
             }
         }
@@ -796,6 +818,12 @@ impl Repr for LoanPath {
                 (format!("$({})", tcx.map.node_to_str(id))).to_string()
             }
 
+            &LpUpvar(ty::UpvarId{ var_id, closure_expr_id }) => {
+                let s = tcx.map.node_to_str(var_id);
+                let s = format!("$({} captured by id={})", s, closure_expr_id);
+                s.to_string()
+            }
+
             &LpExtend(ref lp, _, LpDeref(_)) => {
                 (format!("{}.*", lp.repr(tcx))).to_string()
             }

src/librustc/middle/borrowck/move_data.rs

@@ -231,7 +231,7 @@ impl MoveData {
         }
 
         let index = match *lp {
-            LpVar(..) => {
+            LpVar(..) | LpUpvar(..) => {
                 let index = MovePathIndex(self.paths.borrow().len());
 
                 self.paths.borrow_mut().push(MovePath {
@@ -302,7 +302,7 @@ impl MoveData {
             }
             None => {
                 match **lp {
-                    LpVar(..) => { }
+                    LpVar(..) | LpUpvar(..) => { }
                     LpExtend(ref b, _, _) => {
                         self.add_existing_base_paths(b, result);
                     }
@@ -418,6 +418,11 @@ impl MoveData {
                     let path = *self.path_map.borrow().get(&path.loan_path);
                     self.kill_moves(path, kill_id, dfcx_moves);
                 }
+                LpUpvar(ty::UpvarId { var_id: _, closure_expr_id }) => {
+                    let kill_id = closure_to_block(closure_expr_id, tcx);
+                    let path = *self.path_map.borrow().get(&path.loan_path);
+                    self.kill_moves(path, kill_id, dfcx_moves);
+                }
                 LpExtend(..) => {}
             }
         }
@@ -430,6 +435,10 @@ impl MoveData {
                     let kill_id = tcx.region_maps.var_scope(id);
                     dfcx_assign.add_kill(kill_id, assignment_index);
                 }
+                LpUpvar(ty::UpvarId { var_id: _, closure_expr_id }) => {
+                    let kill_id = closure_to_block(closure_expr_id, tcx);
+                    dfcx_assign.add_kill(kill_id, assignment_index);
+                }
                 LpExtend(..) => {
                     tcx.sess.bug("var assignment for non var path");
                 }

src/librustc/middle/dataflow.rs

@@ -266,34 +266,24 @@ impl<'a, O:DataFlowOperator> DataFlowContext<'a, O> {
 
     pub fn add_gen(&mut self, id: ast::NodeId, bit: uint) {
         //! Indicates that `id` generates `bit`
-        if self.nodeid_to_index.contains_key(&id) {
-            debug!("add_gen(id={:?}, bit={:?})", id, bit);
-            let cfgidx = to_cfgidx_or_die(id, &self.nodeid_to_index);
-            let (start, end) = self.compute_id_range(cfgidx);
-            {
-                let gens = self.gens.mut_slice(start, end);
-                set_bit(gens, bit);
-            }
-        } else {
-            debug!("{:s} add_gen skip (id={:?}, bit={:?}); id not in current fn",
-                   self.analysis_name, id, bit);
-        }
+        debug!("{:s} add_gen(id={:?}, bit={:?})",
+               self.analysis_name, id, bit);
+        assert!(self.nodeid_to_index.contains_key(&id));
+        let cfgidx = to_cfgidx_or_die(id, &self.nodeid_to_index);
+        let (start, end) = self.compute_id_range(cfgidx);
+        let gens = self.gens.mut_slice(start, end);
+        set_bit(gens, bit);
     }
 
     pub fn add_kill(&mut self, id: ast::NodeId, bit: uint) {
         //! Indicates that `id` kills `bit`
-        if self.nodeid_to_index.contains_key(&id) {
-            debug!("add_kill(id={:?}, bit={:?})", id, bit);
-            let cfgidx = to_cfgidx_or_die(id, &self.nodeid_to_index);
-            let (start, end) = self.compute_id_range(cfgidx);
-            {
-                let kills = self.kills.mut_slice(start, end);
-                set_bit(kills, bit);
-            }
-        } else {
-            debug!("{:s} add_kill skip (id={:?}, bit={:?}); id not in current fn",
-                   self.analysis_name, id, bit);
-        }
+        debug!("{:s} add_kill(id={:?}, bit={:?})",
+               self.analysis_name, id, bit);
+        assert!(self.nodeid_to_index.contains_key(&id));
+        let cfgidx = to_cfgidx_or_die(id, &self.nodeid_to_index);
+        let (start, end) = self.compute_id_range(cfgidx);
+        let kills = self.kills.mut_slice(start, end);
+        set_bit(kills, bit);
     }
 
     fn apply_gen_kill(&mut self, cfgidx: CFGIndex, bits: &mut [uint]) {

src/librustc/middle/mem_categorization.rs

@@ -97,6 +97,7 @@ pub enum categorization {
 pub struct CopiedUpvar {
     pub upvar_id: ast::NodeId,
     pub onceness: ast::Onceness,
+    pub capturing_proc: ast::NodeId,
 }
 
 // different kinds of pointers:
@@ -559,7 +560,9 @@ impl<'t,TYPER:Typer> MemCategorizationContext<'t,TYPER> {
                               span:span,
                               cat:cat_copied_upvar(CopiedUpvar {
                                   upvar_id: var_id,
-                                  onceness: closure_ty.onceness}),
+                                  onceness: closure_ty.onceness,
+                                  capturing_proc: fn_node_id,
+                              }),
                               mutbl:McImmutable,
                               ty:expr_ty
                           }))