list: use predicate to enforce non-empty requirement

2 files changed, 6 insertions, 2 deletions

diff --git a/src/comp/middle/last_use.rs b/src/comp/middle/last_use.rs
index 7b1a0b6c0a3..75758c2cdf4 100644
--- a/src/comp/middle/last_use.rs
+++ b/src/comp/middle/last_use.rs
@@ -1,7 +1,7 @@
 import syntax::{visit, ast_util};
 import syntax::ast::*;
 import syntax::codemap::span;
-import std::list::{list, nil, cons, tail};
+import std::list::{is_not_empty, list, nil, cons, tail};
 import core::{vec, option};
 import std::list;
 
@@ -177,7 +177,9 @@ fn visit_block(tp: block_type, cx: ctx, visit: block()) {
     visit();
     local.second = true;
     visit();
-    cx.blocks = tail(cx.blocks);
+    let cx_blocks = cx.blocks;
+    check is_not_empty(cx_blocks);
+    cx.blocks = tail(cx_blocks);
     cx.current = join_branches(local.exits);
 }
 
diff --git a/src/comp/middle/resolve.rs b/src/comp/middle/resolve.rs
index 9eaaee2cb36..ceb8e53f7ce 100644
--- a/src/comp/middle/resolve.rs
+++ b/src/comp/middle/resolve.rs
@@ -266,6 +266,7 @@ fn map_crate(e: @env, c: @ast::crate) {
             let imp = follow_import(*e, sc, *path, vi.span);
             if option::is_some(imp) {
                 let glob = {def: option::get(imp), item: vi};
+                check list::is_not_empty(sc);
                 alt list::head(sc) {
                   scope_item(i) {
                     e.mod_map.get(i.id).glob_imports += [glob];
@@ -455,6 +456,7 @@ fn visit_block_with_scope(b: ast::blk, sc: scopes, v: vt<scopes>) {
 }
 
 fn visit_decl_with_scope(d: @decl, sc: scopes, v: vt<scopes>) {
+    check list::is_not_empty(sc);
     let loc_pos = alt list::head(sc) {
       scope_block(_, _, pos) { pos }
       _ { @mutable 0u }