rustc: Teach rustc to use block results as fn return values. Closes #372

Author: brson

src/comp/middle/trans.rs

@@ -6892,7 +6892,14 @@ fn trans_fn(@local_ctxt cx, &ast::span sp, &ast::_fn f, ast::def_id fid,
 
     auto lltop = bcx.llbb;
 
-    auto res = trans_block(bcx, f.body, return);
+    auto block_ty = node_ann_type(cx.ccx, f.body.node.a);
+    auto res = if (!ty::type_is_nil(cx.ccx.tcx, block_ty)
+                   && !ty::type_is_bot(cx.ccx.tcx, block_ty)) {
+        trans_block(bcx, f.body, save_in(fcx.llretptr))
+    } else {
+        trans_block(bcx, f.body, return)
+    };
+
     if (!is_terminated(res.bcx)) {
         // FIXME: until LLVM has a unit type, we are moving around
         // C_nil values rather than their void type.

src/comp/middle/tstate/pre_post_conditions.rs

@@ -140,6 +140,8 @@ import front::ast::stmt_expr;
 import front::ast::block;
 import front::ast::block_;
 
+import middle::ty::expr_ann;
+
 import util::common::new_def_hash;
 import util::common::decl_lhs;
 import util::common::uistr;
@@ -696,6 +698,15 @@ fn find_pre_post_block(&fn_ctxt fcx, block b) -> () {
 
 fn find_pre_post_fn(&fn_ctxt fcx, &_fn f) -> () {
     find_pre_post_block(fcx, f.body);
+
+    // Treat the tail expression as a return statement
+    alt (f.body.node.expr) {
+        case (some(?tailexpr)) {
+            auto tailann = expr_ann(tailexpr);
+            set_postcond_false(fcx.ccx, tailann);
+        }
+        case (none) { /* fallthrough */ }
+    }
 }
 
 fn fn_pre_post(crate_ctxt ccx, &_fn f, &span sp, &ident i, &def_id id,

src/comp/middle/tstate/states.rs

@@ -150,6 +150,11 @@ import front::ast::stmt_expr;
 import front::ast::block;
 import front::ast::block_;
 
+import middle::ty::expr_ann;
+import middle::ty::expr_ty;
+import middle::ty::type_is_nil;
+import middle::ty::type_is_bot;
+
 import util::common::new_def_hash;
 import util::common::decl_lhs;
 import util::common::uistr;
@@ -753,8 +758,36 @@ fn find_pre_post_state_block(&fn_ctxt fcx, &prestate pres0, &block b)
 
 fn find_pre_post_state_fn(&fn_ctxt fcx, &_fn f) -> bool {
     auto num_local_vars = num_locals(fcx.enclosing);
-    ret find_pre_post_state_block(fcx,
-          empty_prestate(num_local_vars), f.body);
+    auto changed = find_pre_post_state_block(fcx,
+                     empty_prestate(num_local_vars), f.body);
+
+    // Treat the tail expression as a return statement
+    alt (f.body.node.expr) {
+        case (some(?tailexpr)) {
+            auto tailann = expr_ann(tailexpr);
+            auto tailty = expr_ty(fcx.ccx.tcx, tailexpr);
+
+            // Since blocks and alts and ifs that don't have results
+            // implicitly result in nil, we have to be careful to not
+            // interpret nil-typed block results as the result of a
+            // function with some other return type
+            if (!type_is_nil(fcx.ccx.tcx, tailty)
+                && !type_is_bot(fcx.ccx.tcx, tailty)) {
+
+                set_poststate_ann(fcx.ccx, tailann,
+                                  false_postcond(num_local_vars));
+                alt (fcx.enclosing.cf) {
+                    case (noreturn) {
+                        kill_poststate(fcx, tailann, fcx.id);
+                    }
+                    case (_) { }
+                }
+            }
+        }
+        case (none) { /* fallthrough */ }
+    }
+
+    ret changed;
 }
 
 //

src/test/compile-fail/missing-return2.rs

@@ -0,0 +1,14 @@
+// xfail-stage0
+// error-pattern: return
+
+fn f() -> int {
+  // Make sure typestate doesn't interpret this alt expression
+  // as the function result
+  alt (true) {
+    case (true) {
+    }
+  }
+}
+
+fn main() {
+}

src/test/run-fail/expr-fn-fail.rs

@@ -0,0 +1,8 @@
+// xfail-stage0
+// error-pattern:explicit failure
+
+fn f() -> ! { fail }
+
+fn main() {
+  f();
+}

src/test/run-pass/expr-fn.rs

@@ -0,0 +1,65 @@
+// xfail-stage0
+
+fn test_int() {
+  fn f() -> int { 10 }
+  assert (f() == 10);
+}
+
+fn test_vec() {
+  fn f() -> vec[int] { [10, 11] }
+  assert (f().(1) == 11);
+}
+
+fn test_generic() {
+  fn f[T](&T t) -> T { t }
+  assert (f(10) == 10);
+}
+
+fn test_alt() {
+  fn f() -> int {
+    alt (true) {
+      case (false) { 10 }
+      case (true) { 20 }
+    }
+  }
+  assert (f() == 20);
+}
+
+fn test_if() {
+  fn f() -> int { if (true) { 10 } else { 20 } }
+  assert (f() == 10);
+}
+
+fn test_block() {
+  fn f() -> int {{ 10 }}
+  assert (f() == 10);
+}
+
+fn test_ret() {
+  fn f() -> int {
+    ret 10 // no semi
+  }
+  assert (f() == 10);
+}
+
+// From issue #372
+fn test_372() {
+  fn f() -> int { auto x = { 3 }; x }
+  assert (f() == 3);
+}
+
+fn test_nil() {
+  ()
+}
+
+fn main() {
+  test_int();
+  test_vec();
+  test_generic();
+  test_alt();
+  test_if();
+  test_block();
+  test_ret();
+  test_372();
+  test_nil();
+}