Return expressions can be empty which us unit-type

The parser has the same bug as in #225 for break expressions. This
tidies up the type resolver and GENERIC translation to handle the
case where there is no return expression as well.

Fixes #226

4 files changed, 33 insertions, 7 deletions

diff --git a/gcc/rust/backend/rust-compile-expr.h b/gcc/rust/backend/rust-compile-expr.h
index 92cb392..0c8d25a 100644
--- a/gcc/rust/backend/rust-compile-expr.h
+++ b/gcc/rust/backend/rust-compile-expr.h
@@ -84,14 +84,18 @@ public:
 
   void visit (HIR::ReturnExpr &expr)
   {
-    Bexpression *compiled_expr
-      = CompileExpr::Compile (expr.return_expr.get (), ctx);
-    rust_assert (compiled_expr != nullptr);
-
     auto fncontext = ctx->peek_fn ();
 
     std::vector<Bexpression *> retstmts;
-    retstmts.push_back (compiled_expr);
+    if (expr.has_return_expr ())
+      {
+	Bexpression *compiled_expr
+	  = CompileExpr::Compile (expr.return_expr.get (), ctx);
+	rust_assert (compiled_expr != nullptr);
+
+	retstmts.push_back (compiled_expr);
+      }
+
     auto s = ctx->get_backend ()->return_statement (fncontext.fndecl, retstmts,
 						    expr.get_locus ());
     ctx->add_statement (s);
diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 18e6983..fcb3d18 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -7400,8 +7400,10 @@ Parser<ManagedTokenSource>::parse_return_expr (
     }
 
   // parse expression to return, if it exists
-  std::unique_ptr<AST::Expr> returned_expr = parse_expr ();
-  // FIXME: ensure this doesn't ruin the middle of any expressions or anything
+  ParseRestrictions restrictions;
+  restrictions.expr_can_be_null = true;
+  std::unique_ptr<AST::Expr> returned_expr
+    = parse_expr (std::vector<AST::Attribute> (), restrictions);
 
   return std::unique_ptr<AST::ReturnExpr> (
     new AST::ReturnExpr (locus, std::move (returned_expr),
diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.h b/gcc/rust/typecheck/rust-hir-type-check-expr.h
index 9fe6e4f..c8493f0 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.h
@@ -137,6 +137,12 @@ public:
 
   void visit (HIR::ReturnExpr &expr)
   {
+    if (!expr.has_return_expr ())
+      {
+	infered = new TyTy::UnitType (expr.get_mappings ().get_hirid ());
+	return;
+      }
+
     auto fn_return_tyty = context->peek_return_type ();
     rust_assert (fn_return_tyty != nullptr);
 
diff --git a/gcc/testsuite/rust.test/compilable/loop3.rs b/gcc/testsuite/rust.test/compilable/loop3.rs
new file mode 100644
index 0000000..76fadfb
--- /dev/null
+++ b/gcc/testsuite/rust.test/compilable/loop3.rs
@@ -0,0 +1,14 @@
+fn main() {
+    let mut a = 1;
+    let mut b = 1;
+
+    // first number in Fibonacci sequence over 10:
+    loop {
+        if b > 10 {
+            return;
+        }
+        let c = a + b;
+        a = b;
+        b = c;
+    }
+}