Handle sequential let semantics properly in typestate

Closes #824

src/comp/middle/tstate/pre_post_conditions.rs

@@ -4,20 +4,7 @@ import std::option;
 import std::option::none;
 import std::option::some;
 
-import tstate::ann::pre_and_post;
-import tstate::ann::get_post;
-import tstate::ann::postcond;
-import tstate::ann::true_precond;
-import tstate::ann::false_postcond;
-import tstate::ann::empty_poststate;
-import tstate::ann::require;
-import tstate::ann::require_and_preserve;
-import tstate::ann::union;
-import tstate::ann::intersect;
-import tstate::ann::pp_clone;
-import tstate::ann::empty_prestate;
-import tstate::ann::set_precondition;
-import tstate::ann::set_postcondition;
+import tstate::ann::*;
 import aux::*;
 import bitvectors::bit_num;
 import bitvectors::promises;
@@ -28,7 +15,7 @@ import bitvectors::declare_var;
 import bitvectors::gen_poststate;
 import bitvectors::relax_precond_block;
 import bitvectors::gen;
-import tritv::tritv_clone;
+import tritv::*;
 import syntax::ast::*;
 import syntax::visit;
 import std::map::new_int_hash;
@@ -591,6 +578,8 @@ fn find_pre_post_stmt(fcx: &fn_ctxt, s: &stmt) {
  stmt_decl(adecl, id) {
  alt adecl.node {
  decl_local(alocals) {
+ let e_pp;
+ let prev_pp = empty_pre_post(num_constraints(fcx.enclosing));
  for alocal: @local in alocals {
  alt alocal.node.init {
  some(an_init) {
@@ -611,7 +600,16 @@ fn find_pre_post_stmt(fcx: &fn_ctxt, s: &stmt) {
  }
 
  for each pat: @pat in pat_bindings(alocal.node.pat) {
- let ident = alt pat.node { pat_bind(n) { n } };
+ /* FIXME: This won't be necessary when typestate
+ works well enough for pat_bindings to return a
+ refinement-typed thing. */
+ let ident = alt pat.node {
+ pat_bind(n) { n }
+ _ {
+ fcx.ccx.tcx.sess.span_bug(pat.span,
+ "Impossible LHS");
+ }
+ };
  alt p {
  some(p) {
  copy_in_postcond(fcx, id,
@@ -629,6 +627,29 @@ fn find_pre_post_stmt(fcx: &fn_ctxt, s: &stmt) {
  if an_init.op == init_move && is_path(an_init.expr) {
  forget_in_postcond(fcx, id, an_init.expr.id);
  }
+
+ /* Clear out anything that the previous initializer
+ guaranteed */
+ e_pp = expr_pp(fcx.ccx, an_init.expr);
+ tritv_copy(prev_pp.precondition,
+ seq_preconds(fcx, [prev_pp, e_pp]));
+ /* Include the LHSs too, since those aren't in the
+ postconds of the RHSs themselves */
+ for each pat: @pat in pat_bindings(alocal.node.pat) {
+ alt pat.node {
+ pat_bind(n) {
+ set_in_postcond(bit_num(fcx, ninit(pat.id, n)),
+ prev_pp);
+ }
+ _ {
+ fcx.ccx.tcx.sess.span_bug(pat.span,
+ "Impossible LHS");
+ }
+ };
+ }
+ copy_pre_post_(fcx.ccx, id,
+ prev_pp.precondition,
+ prev_pp.postcondition);
  }
  none. {
  for each p: @pat in pat_bindings(alocal.node.pat) {

src/test/run-pass/multi-let.rs

@@ -0,0 +1,4 @@
+fn main() {
+ let x = 10, y = x;
+ assert (y == 10);
+}