rustc: Add a region checking pass

Errors aren't reported yet, because the regions aren't properly inferred from the & operator at the moment and that would break the tests.

Author: pcwalton

src/rustc/driver/driver.rs

@@ -163,6 +163,8 @@ fn compile_upto(sess: session, cfg: ast::crate_cfg,
     let mutbl_map =
         time(time_passes, "mutability checking",
              bind middle::mutbl::check_crate(ty_cx, crate));
+    time(time_passes, "region checking",
+         bind middle::regionck::check_crate(ty_cx, crate));
     let (copy_map, ref_map) =
         time(time_passes, "alias checking",
              bind middle::alias::check_crate(ty_cx, crate));

src/rustc/middle/regionck.rs

@@ -0,0 +1,71 @@
+/*
+ * The region checking pass. Ensures that region-annotated pointers never
+ * outlive their referents.
+ */
+
+import driver::session::session;
+import middle::ty;
+import std::map::hashmap;
+import syntax::{ast, visit};
+
+type ctxt = {
+    tcx: ty::ctxt,
+    enclosing_block: option<ast::node_id>
+};
+
+fn check_expr(expr: @ast::expr, cx: ctxt, visitor: visit::vt<ctxt>) {
+    ty::walk_ty(cx.tcx, ty::expr_ty(cx.tcx, expr)) { |t|
+        alt ty::get(t).struct {
+            ty::ty_rptr(region, _) {
+                alt region {
+                    ty::re_named(_) | ty::re_caller(_) { /* ok */ }
+                    ty::re_block(rbi) {
+                        let referent_block_id = rbi;
+                        let enclosing_block_id = alt cx.enclosing_block {
+                            none {
+                                cx.tcx.sess.span_bug(expr.span, "block " +
+                                                     "region type outside " +
+                                                     "a block?!");
+                            }
+                            some(eb) { eb }
+                        };
+
+                        let parent_blocks = cx.tcx.region_map.parent_blocks;
+                        while enclosing_block_id != referent_block_id {
+                            if parent_blocks.contains_key(referent_block_id) {
+                                referent_block_id =
+                                    parent_blocks.get(referent_block_id);
+                            } else {
+                                // TODO: Enable this.
+
+                                //cx.tcx.sess.span_err(expr.span,
+                                //                     "reference escapes " +
+                                //                     "its block");
+                                break;
+                            }
+                        }
+                    }
+                }
+            }
+            _ { /* no-op */ }
+        }
+    }
+
+    visit::visit_expr(expr, cx, visitor);
+}
+
+fn check_block(blk: ast::blk, cx: ctxt, visitor: visit::vt<ctxt>) {
+    let new_cx: ctxt = { enclosing_block: some(blk.node.id) with cx };
+    visit::visit_block(blk, new_cx, visitor);
+}
+
+fn check_crate(ty_cx: ty::ctxt, crate: @ast::crate) {
+    let cx: ctxt = {tcx: ty_cx, enclosing_block: none};
+    let visitor = visit::mk_vt(@{
+        visit_expr: check_expr,
+        visit_block: check_block
+        with *visit::default_visitor()
+    });
+    visit::visit_crate(*crate, cx, visitor);
+}
+

src/rustc/rustc.rc

@@ -45,6 +45,7 @@ mod middle {
     mod capture;
     mod pat_util;
     mod region;
+    mod regionck;
 
     mod tstate {
         mod ck;