1 files changed, 69 insertions, 0 deletions
diff --git a/src/libsyntax/parse/classify.rs b/src/libsyntax/parse/classify.rs
new file mode 100644
index 00000000000..471fe15788d
--- /dev/null
+++ b/src/libsyntax/parse/classify.rs
@@ -0,0 +1,69 @@
+/*
+  Predicates on exprs and stmts that the pretty-printer and parser use
+ */
+import ast_util::*;
+
+fn expr_requires_semi_to_be_stmt(e: @ast::expr) -> bool {
+    alt e.node {
+      ast::expr_if(_, _, _) | ast::expr_if_check(_, _, _)
+      | ast::expr_alt(_, _, _) | ast::expr_block(_)
+      | ast::expr_while(_, _) | ast::expr_loop(_)
+      | ast::expr_call(_, _, true) {
+        false
+      }
+      _ { true }
+    }
+}
+
+fn stmt_ends_with_semi(stmt: ast::stmt) -> bool {
+    alt stmt.node {
+      ast::stmt_decl(d, _) {
+        ret alt d.node {
+              ast::decl_local(_) { true }
+              ast::decl_item(_) { false }
+            }
+      }
+      ast::stmt_expr(e, _) {
+        ret expr_requires_semi_to_be_stmt(e);
+      }
+      ast::stmt_semi(e, _) {
+        ret false;
+      }
+    }
+}
+
+fn need_parens(expr: @ast::expr, outer_prec: uint) -> bool {
+    alt expr.node {
+      ast::expr_binary(op, _, _) { operator_prec(op) < outer_prec }
+      ast::expr_cast(_, _) { parse::prec::as_prec < outer_prec }
+      // This may be too conservative in some cases
+      ast::expr_assign(_, _) { true }
+      ast::expr_move(_, _) { true }
+      ast::expr_swap(_, _) { true }
+      ast::expr_assign_op(_, _, _) { true }
+      ast::expr_ret(_) { true }
+      ast::expr_assert(_) { true }
+      ast::expr_check(_, _) { true }
+      ast::expr_log(_, _, _) { true }
+      _ { !parse::classify::expr_requires_semi_to_be_stmt(expr) }
+    }
+}
+
+fn ends_in_lit_int(ex: @ast::expr) -> bool {
+    alt ex.node {
+      ast::expr_lit(@{node: ast::lit_int(_, ast::ty_i), _}) { true }
+      ast::expr_binary(_, _, sub) | ast::expr_unary(_, sub) |
+      ast::expr_move(_, sub) | ast::expr_copy(sub) |
+      ast::expr_assign(_, sub) |
+      ast::expr_assign_op(_, _, sub) | ast::expr_swap(_, sub) |
+      ast::expr_log(_, _, sub) | ast::expr_assert(sub) |
+      ast::expr_check(_, sub) { ends_in_lit_int(sub) }
+      ast::expr_fail(osub) | ast::expr_ret(osub) {
+        alt osub {
+          some(ex) { ends_in_lit_int(ex) }
+          _ { false }
+        }
+      }
+      _ { false }
+    }
+}