Add support for empty struct initilizer

Rust supports unit struct initilization such as S{} this takes this tree
and resolves it fully. This should really be all desugared via HIR but that
is in progress in another PR.

5 files changed, 60 insertions, 0 deletions

diff --git a/gcc/rust/backend/rust-compile-expr.h b/gcc/rust/backend/rust-compile-expr.h
index e92c7cd..fc8ad81 100644
--- a/gcc/rust/backend/rust-compile-expr.h
+++ b/gcc/rust/backend/rust-compile-expr.h
@@ -527,6 +527,20 @@ public:
       }
   }
 
+  void visit (HIR::StructExprStruct &struct_expr) override
+  {
+    TyTy::BaseType *tyty = nullptr;
+    if (!ctx->get_tyctx ()->lookup_type (
+	  struct_expr.get_mappings ().get_hirid (), &tyty))
+      {
+	rust_error_at (struct_expr.get_locus (), "unknown type");
+	return;
+      }
+
+    rust_assert (tyty->is_unit ());
+    translated = ctx->get_backend ()->unit_expression ();
+  }
+
   void visit (HIR::StructExprStructFields &struct_expr) override
   {
     TyTy::BaseType *tyty = nullptr;
diff --git a/gcc/rust/hir/rust-ast-lower-expr.h b/gcc/rust/hir/rust-ast-lower-expr.h
index 82d13d0..19ce8c2 100644
--- a/gcc/rust/hir/rust-ast-lower-expr.h
+++ b/gcc/rust/hir/rust-ast-lower-expr.h
@@ -467,6 +467,24 @@ public:
 				 expr.get_locus ());
   }
 
+  void visit (AST::StructExprStruct &struct_expr) override
+  {
+    HIR::PathInExpression *path
+      = ASTLowerPathInExpression::translate (&struct_expr.get_struct_name ());
+    HIR::PathInExpression copied_path (*path);
+    delete path;
+
+    auto crate_num = mappings->get_current_crate ();
+    Analysis::NodeMapping mapping (crate_num, struct_expr.get_node_id (),
+				   mappings->get_next_hir_id (crate_num),
+				   UNKNOWN_LOCAL_DEFID);
+
+    translated = new HIR::StructExprStruct (mapping, copied_path,
+					    struct_expr.get_inner_attrs (),
+					    struct_expr.get_outer_attrs (),
+					    struct_expr.get_locus ());
+  }
+
   void visit (AST::StructExprStructFields &struct_expr) override
   {
     // bit of a hack for now
diff --git a/gcc/rust/resolve/rust-ast-resolve-expr.h b/gcc/rust/resolve/rust-ast-resolve-expr.h
index f163ef5b..bbd8818 100644
--- a/gcc/rust/resolve/rust-ast-resolve-expr.h
+++ b/gcc/rust/resolve/rust-ast-resolve-expr.h
@@ -219,6 +219,14 @@ public:
     ResolveExpr::go (elems.get_elem_to_copy ().get (), elems.get_node_id ());
   }
 
+  // this this an empty struct constructor like 'S {}'
+  void visit (AST::StructExprStruct &struct_expr) override
+  {
+    ResolveExpr::go (&struct_expr.get_struct_name (),
+		     struct_expr.get_node_id ());
+  }
+
+  // this this a struct constructor with fields
   void visit (AST::StructExprStructFields &struct_expr) override
   {
     ResolveExpr::go (&struct_expr.get_struct_name (),
diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.h b/gcc/rust/typecheck/rust-hir-type-check-expr.h
index 236c7b9..bdebfd3 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.h
@@ -827,6 +827,21 @@ public:
       = TypeCheckExpr::Resolve (elems.get_elem_to_copy (), false);
   }
 
+  // empty struct
+  void visit (HIR::StructExprStruct &struct_expr) override
+  {
+    TyTy::BaseType *struct_path_ty
+      = TypeCheckExpr::Resolve (&struct_expr.get_struct_name (), false);
+    if (struct_path_ty->get_kind () != TyTy::TypeKind::ADT)
+      {
+	rust_error_at (struct_expr.get_struct_name ().get_locus (),
+		       "expected an ADT type for constructor");
+	return;
+      }
+
+    infered = struct_path_ty;
+  }
+
   void visit (HIR::StructExprStructFields &struct_expr) override
   {
     infered = TypeCheckStructExpr::Resolve (&struct_expr);
diff --git a/gcc/testsuite/rust/compile/torture/unit_type4.rs b/gcc/testsuite/rust/compile/torture/unit_type4.rs
new file mode 100644
index 0000000..ccbfa21
--- /dev/null
+++ b/gcc/testsuite/rust/compile/torture/unit_type4.rs
@@ -0,0 +1,5 @@
+struct S;
+
+fn main() {
+    let _s = S {};
+}