Fix C++ compatibility of unions with degenerate variant names

This fixes the C codegen so that when a union has a variant with the same name as the union, the generated code can be compiled as C or C++.

Prior to this change it was valid C but not valid C++ due to differences in the rules for anonymous structs.

I also added a test that fails before this change and passes afterwards.

src/sail_c_backend/c_backend.ml

@@ -962,7 +962,7 @@ let rec sgen_cval = function
   | V_struct (fields, _) ->
       Printf.sprintf "{%s}"
         (Util.string_of_list ", " (fun (field, cval) -> zencode_id field ^ " = " ^ sgen_cval cval) fields)
-  | V_ctor_unwrap (f, ctor, _) -> Printf.sprintf "%s.%s" (sgen_cval f) (sgen_uid ctor)
+  | V_ctor_unwrap (f, ctor, _) -> Printf.sprintf "%s.variants.%s" (sgen_cval f) (sgen_uid ctor)
   | V_tuple _ -> Reporting.unreachable Parse_ast.Unknown __POS__ "Cannot generate C value for a tuple literal"
 
 and sgen_call op cvals =
@@ -1475,7 +1475,8 @@ let codegen_type_def =
         c_function ~return:"static void" (sail_create n "struct %s *op" n)
           ([string (Printf.sprintf "op->kind = Kind_%s;" (sgen_id ctor_id))]
           @
-          if not (is_stack_ctyp ctyp) then [sail_create ~suffix:";" (sgen_ctyp_name ctyp) "&op->%s" (sgen_id ctor_id)]
+          if not (is_stack_ctyp ctyp) then
+            [sail_create ~suffix:";" (sgen_ctyp_name ctyp) "&op->variants.%s" (sgen_id ctor_id)]
           else []
           )
       in
@@ -1485,7 +1486,7 @@ let codegen_type_def =
       in
       let clear_field v ctor_id ctyp =
         if is_stack_ctyp ctyp then None
-        else Some (sail_kill ~suffix:";" (sgen_ctyp_name ctyp) "&%s->%s" v (sgen_id ctor_id))
+        else Some (sail_kill ~suffix:";" (sgen_ctyp_name ctyp) "&%s->variants.%s" v (sgen_id ctor_id))
       in
       let codegen_clear =
         let n = sgen_id id in
@@ -1499,23 +1500,24 @@ let codegen_type_def =
           )
           ([each_ctor "rop->" (clear_field "rop") tus; string ("rop->kind = Kind_" ^ sgen_id ctor_id) ^^ semi]
           @
-          if is_stack_ctyp ctyp then [ksprintf string "rop->%s = op;" (sgen_id ctor_id)]
+          if is_stack_ctyp ctyp then [ksprintf string "rop->variants.%s = op;" (sgen_id ctor_id)]
           else
             [
-              sail_create ~suffix:";" (sgen_ctyp_name ctyp) "&rop->%s" (sgen_id ctor_id);
-              sail_copy ~suffix:";" (sgen_ctyp_name ctyp) "&rop->%s, op" (sgen_id ctor_id);
+              sail_create ~suffix:";" (sgen_ctyp_name ctyp) "&rop->variants.%s" (sgen_id ctor_id);
+              sail_copy ~suffix:";" (sgen_ctyp_name ctyp) "&rop->variants.%s, op" (sgen_id ctor_id);
             ]
           )
       in
       let codegen_setter =
         let n = sgen_id id in
         let set_field ctor_id ctyp =
           Some
-            ( if is_stack_ctyp ctyp then string (Printf.sprintf "rop->%s = op.%s;" (sgen_id ctor_id) (sgen_id ctor_id))
+            ( if is_stack_ctyp ctyp then
+                string (Printf.sprintf "rop->variants.%s = op.variants.%s;" (sgen_id ctor_id) (sgen_id ctor_id))
               else
-                sail_create ~suffix:";" (sgen_ctyp_name ctyp) "&rop->%s" (sgen_id ctor_id)
-                ^^ sail_copy ~prefix:" " ~suffix:";" (sgen_ctyp_name ctyp) "&rop->%s, op.%s" (sgen_id ctor_id)
-                     (sgen_id ctor_id)
+                sail_create ~suffix:";" (sgen_ctyp_name ctyp) "&rop->variants.%s" (sgen_id ctor_id)
+                ^^ sail_copy ~prefix:" " ~suffix:";" (sgen_ctyp_name ctyp) "&rop->variants.%s, op.variants.%s"
+                     (sgen_id ctor_id) (sgen_id ctor_id)
             )
         in
         c_function ~return:"static void"
@@ -1528,7 +1530,8 @@ let codegen_type_def =
       in
       let codegen_eq =
         let codegen_eq_test ctor_id ctyp =
-          c_return (sail_equal (sgen_ctyp_name ctyp) "op1.%s, op2.%s" (sgen_id ctor_id) (sgen_id ctor_id))
+          c_return
+            (sail_equal (sgen_ctyp_name ctyp) "op1.variants.%s, op2.variants.%s" (sgen_id ctor_id) (sgen_id ctor_id))
         in
         let rec codegen_eq_tests = function
           | [] -> c_return (string "false")
@@ -1559,7 +1562,7 @@ let codegen_type_def =
                   (separate space [string "enum"; string ("kind_" ^ sgen_id id); string "kind" ^^ semi]
                   ^^ hardline ^^ string "union" ^^ space
                   ^^ surround 2 0 lbrace (separate_map (semi ^^ hardline) codegen_tu tus ^^ semi) rbrace
-                  ^^ semi
+                  ^^ space ^^ string "variants" ^^ semi
                   )
                   rbrace
              ^^ semi;

test/c/run_tests.py

@@ -29,9 +29,6 @@ def no_valgrind():
 def test_c(name, c_opts, sail_opts, valgrind, compiler='cc'):
     banner('Testing {} with C options: {} Sail options: {} valgrind: {}'.format(name, c_opts, sail_opts, valgrind))
     results = Results(name)
-    if compiler == 'c++':
-        # tl_pat.c:66:31: error: ‘zX::<unnamed union>::<unnamed struct>::zX’ has the same name as the class in which it is declared
-        results.expect_failure("tl_pat.sail", "same name as the class in which it is declared")
     if valgrind and no_valgrind():
         print('skipping because no valgrind found')
         return results.finish()

test/c/union_variant_names.expect

@@ -0,0 +1 @@
+22

test/c/union_variant_names.sail

@@ -0,0 +1,36 @@
+default Order dec
+
+$include <prelude.sail>
+$include <string.sail>
+
+// Ensure that unions with variants that match the union name work.
+// In the past the generated C code was not compatible with C++ due
+// to different rules around anonymous unions.
+
+union n0 = {
+    n0 : int,
+}
+
+union n1 = {
+    n2 : int,
+    n1 : int,
+}
+
+// newtype is syntactic sugar for a single entry union.
+newtype n3 = n3 : int
+
+enum n4 = { n4 }
+
+function main() -> unit = {
+  // Prevent dead-code elimination of the types.
+  // This is not very robust but it works for now.
+  let v0 = n0(1);
+  let v1 = n1(2);
+  let v3 = n3(3);
+  let v4 = n4;
+  let x : int = match v1 {
+    n2(d) => d + 10,
+    n1(d) => d + 20,
+  };
+  print_endline(dec_str(x));
+}