Issue #2657: track mutability of bindings, also prevent move from bindings

Author: nikomatsakis

src/libsyntax/parse/lexer.rs

@@ -154,7 +154,7 @@ fn tt_next_token(&&r: tt_reader) -> {tok: token::token, sp: span} {
             ret ret_val;
           }
           tt_frame_up(option::some(tt_f)) {
-            r.cur <- tt_f;
+            r.cur = tt_f;
             /* the above `if` would need to be a `while` if we didn't know
             that the last thing in a `tt_delim` is always a `tt_flat` */
             r.cur.idx += 1u;

src/rustc/middle/borrowck.rs

@@ -175,6 +175,7 @@ fn check_crate(tcx: ty::ctxt,
     let bccx = @{tcx: tcx,
                  method_map: method_map,
                  last_use_map: last_use_map,
+                 binding_map: int_hash(),
                  root_map: root_map(),
                  mutbl_map: int_hash()};
 
@@ -189,6 +190,7 @@ fn check_crate(tcx: ty::ctxt,
 type borrowck_ctxt = @{tcx: ty::ctxt,
                        method_map: typeck::method_map,
                        last_use_map: liveness::last_use_map,
+                       binding_map: binding_map,
                        root_map: root_map,
                        mutbl_map: mutbl_map};
 
@@ -208,6 +210,10 @@ type root_map_key = {id: ast::node_id, derefs: uint};
 // this is used in trans for optimization purposes.
 type mutbl_map = std::map::hashmap<ast::node_id, ()>;
 
+// maps from each binding's id to the mutability of the location it
+// points at.  See gather_loan.rs for more detail (search for binding_map)
+type binding_map = std::map::hashmap<ast::node_id, ast::mutability>;
+
 // Errors that can occur"]
 enum bckerr_code {
     err_mut_uniq,
@@ -228,6 +234,7 @@ enum categorization {
     cat_rvalue,                     // result of eval'ing some misc expr
     cat_special(special_kind),      //
     cat_local(ast::node_id),        // local variable
+    cat_binding(ast::node_id),      // pattern binding
     cat_arg(ast::node_id),          // formal argument
     cat_stack_upvar(cmt),           // upvar in stack closure
     cat_deref(cmt, uint, ptr_kind), // deref of a ptr
@@ -381,6 +388,7 @@ impl to_str_methods for borrowck_ctxt {
           cat_stack_upvar(_) { "stack-upvar" }
           cat_rvalue { "rvalue" }
           cat_local(node_id) { #fmt["local(%d)", node_id] }
+          cat_binding(node_id) { #fmt["binding(%d)", node_id] }
           cat_arg(node_id) { #fmt["arg(%d)", node_id] }
           cat_deref(cmt, derefs, ptr) {
             #fmt["%s->(%s, %u)", self.cat_to_repr(cmt.cat),
@@ -466,6 +474,7 @@ impl to_str_methods for borrowck_ctxt {
           cat_special(sk_heap_upvar) { "variable declared in an outer block" }
           cat_rvalue { "non-lvalue" }
           cat_local(_) { mut_str + " local variable" }
+          cat_binding(_) { "pattern binding" }
           cat_arg(_) { "argument" }
           cat_deref(_, _, pk) { #fmt["dereference of %s %s pointer",
                                      mut_str, self.pk_to_sigil(pk)] }

src/rustc/middle/borrowck/categorization.rs

@@ -265,12 +265,16 @@ impl public_methods for borrowck_ctxt {
               mutbl:m, ty:expr_ty}
           }
 
-          ast::def_binding(vid) {
-            // no difference between a binding and any other local variable
-            // from out point of view, except that they are always immutable
+          ast::def_binding(pid) {
+            // bindings are "special" since they are implicit pointers.
+
+            // lookup the mutability for this binding that we found in
+            // gather_loans when we categorized it
+            let mutbl = self.binding_map.get(pid);
+
             @{id:id, span:span,
-              cat:cat_local(vid), lp:some(@lp_local(vid)),
-              mutbl:m_imm, ty:expr_ty}
+              cat:cat_binding(pid), lp:none,
+              mutbl:mutbl, ty:expr_ty}
           }
         }
     }

src/rustc/middle/borrowck/gather_loans.rs

@@ -364,6 +364,16 @@ impl methods for gather_loan_ctxt {
             // cat_discr in the method preserve():
             let cmt1 = self.bccx.cat_discr(cmt, alt_id);
             let arm_scope = ty::re_scope(arm_id);
+
+            // Remember the mutability of the location that this
+            // binding refers to.  This will be used later when
+            // categorizing the binding.  This is a bit of a hack that
+            // would be better fixed by #2329; in that case we could
+            // allow the user to specify if they want an imm, const,
+            // or mut binding, or else just reflect the mutability
+            // through the type of the region pointer.
+            self.bccx.binding_map.insert(pat.id, cmt1.mutbl);
+
             self.guarantee_valid(cmt1, m_const, arm_scope);
 
             for o_pat.each { |p|

src/rustc/middle/borrowck/loan.rs

@@ -43,7 +43,7 @@ impl loan_methods for loan_ctxt {
         }
 
         alt cmt.cat {
-          cat_rvalue | cat_special(_) {
+          cat_binding(_) | cat_rvalue | cat_special(_) {
             // should never be loanable
             self.bccx.tcx.sess.span_bug(
                 cmt.span,

src/rustc/middle/borrowck/preserve.rs

@@ -29,6 +29,12 @@ impl public_methods for borrowck_ctxt {
             }
             ok(())
           }
+          cat_binding(_) {
+            // Bindings are these kind of weird implicit pointers (cc
+            // #2329).  We require (in gather_loans) that they be
+            // rooted in an immutable location.
+            ok(())
+          }
           cat_arg(_) {
             // This can happen as not all args are lendable (e.g., &&
             // modes).  In that case, the caller guarantees stability.

src/rustc/middle/trans/base.rs

@@ -3335,7 +3335,7 @@ fn need_invoke(bcx: block) -> bool {
     loop {
         alt cur.kind {
           block_scope(inf) {
-            for inf.cleanups.each {|cleanup|
+            for vec::each(inf.cleanups) {|cleanup|
                 alt cleanup {
                   clean(_, cleanup_type) | clean_temp(_, _, cleanup_type) {
                     if cleanup_type == normal_exit_and_unwind {

src/test/compile-fail/borrowck-binding-mutbl.rs

@@ -0,0 +1,13 @@
+fn impure(_v: [int]) {
+}
+
+fn main() {
+    let x = {mut f: [3]};
+
+    alt x {
+      {f: v} => {
+        impure(v); //! ERROR illegal borrow unless pure: unique value in aliasable, mutable location
+        //!^ NOTE impure due to access to impure function
+      }
+    }
+}