Correct mismatch between the way that pattern ids and expression ids map to types (pattern ids map to the input type, expression ids map to the output type)

Author: nikomatsakis

src/librustc/middle/borrowck/check_loans.rs

@@ -378,7 +378,7 @@ pub impl<'self> CheckLoanCtxt<'self> {
                     // Dynamically check writes to `@mut`
 
                     let key = root_map_key {
-                        id: base.id,
+                        id: guarantor.id,
                         derefs: deref_count
                     };
                     debug!("Inserting write guard at %?", key);

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

@@ -97,7 +97,7 @@ impl GuaranteeLifetimeContext {
                 );
 
                 if !omit_root {
-                    self.check_root(base, derefs, ptr_mutbl, discr_scope);
+                    self.check_root(cmt, base, derefs, ptr_mutbl, discr_scope);
                 } else {
                     debug!("omitting root, base=%s, base_scope=%?",
                            base.repr(self.tcx()), base_scope);
@@ -168,12 +168,14 @@ impl GuaranteeLifetimeContext {
     }
 
     fn check_root(&self,
+                  cmt_deref: mc::cmt,
                   cmt_base: mc::cmt,
                   derefs: uint,
                   ptr_mutbl: ast::mutability,
                   discr_scope: Option<ast::node_id>) {
-        debug!("check_root(cmt_base=%s, derefs=%? ptr_mutbl=%?, \
+        debug!("check_root(cmt_deref=%s, cmt_base=%s, derefs=%?, ptr_mutbl=%?, \
                 discr_scope=%?)",
+               cmt_deref.repr(self.tcx()),
                cmt_base.repr(self.tcx()),
                derefs,
                ptr_mutbl,
@@ -234,7 +236,7 @@ impl GuaranteeLifetimeContext {
         };
 
         // Add a record of what is required
-        let rm_key = root_map_key {id: cmt_base.id, derefs: derefs};
+        let rm_key = root_map_key {id: cmt_deref.id, derefs: derefs};
         let root_info = RootInfo {scope: root_scope, freeze: opt_dyna};
         self.bccx.root_map.insert(rm_key, root_info);
 

src/librustc/middle/borrowck/mod.rs

@@ -172,11 +172,19 @@ pub struct BorrowStats {
 
 pub type LoanMap = @mut HashMap<ast::node_id, @Loan>;
 
-// the keys to the root map combine the `id` of the expression with
-// the number of types that it is autodereferenced. So, for example,
-// if you have an expression `x.f` and x has type ~@T, we could add an
-// entry {id:x, derefs:0} to refer to `x` itself, `{id:x, derefs:1}`
-// to refer to the deref of the unique pointer, and so on.
+// The keys to the root map combine the `id` of the deref expression
+// with the number of types that it is *autodereferenced*. So, for
+// example, imagine I have a variable `x: @@@T` and an expression
+// `(*x).f`.  This will have 3 derefs, one explicit and then two
+// autoderefs. These are the relevant `root_map_key` values that could
+// appear:
+//
+//    {id:*x, derefs:0} --> roots `x` (type: @@@T, due to explicit deref)
+//    {id:*x, derefs:1} --> roots `*x` (type: @@T, due to autoderef #1)
+//    {id:*x, derefs:2} --> roots `**x` (type: @T, due to autoderef #2)
+//
+// Note that there is no entry with derefs:3---the type of that expression
+// is T, which is not a box.
 #[deriving(Eq, IterBytes)]
 pub struct root_map_key {
     id: ast::node_id,