Fix parser bug with builtin function using builtin struct.

The issue was that we add the binding of the struct name twice, binding it first to the NameDef and then refining it to point to the StructDef. The special handling in bindings.h for the builtins module was not precise enough and would cause it to ignore the redefinition, leaving the name unexpectedly bound to the NameDef instead of the StructDef.

PiperOrigin-RevId: 863021072

Author: richmckeever

xls/dslx/frontend/bindings.h

@@ -150,8 +150,12 @@ class Bindings {
     // NameDefs shadow the corresponding BuiltinNameDefs for the same entities.
     // Without this check, a builtin that uses another builtin in its signature
     // would cause problems in type concretization.
-    if (IsBuiltinModule() && ResolveNode(name).has_value()) {
-      return;
+    if (IsBuiltinModule()) {
+      std::optional<BoundNode> existing = ResolveNode(name);
+      if (existing.has_value() &&
+          std::holds_alternative<BuiltinNameDef*>(*existing)) {
+        return;
+      }
     }
     local_bindings_[std::move(name)] = binding;
   }

xls/dslx/frontend/builtin_stubs.x

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+struct State<T: type> {}
+
 fn and_reduce<N: u32>(x: uN[N]) -> u1;
 
 fn array_rev<T: type, N: u32>(x: T[N]) -> T[N];
@@ -71,6 +73,8 @@ fn or_reduce<N: u32>(x: uN[N]) -> u1;
 
 fn priority_sel<N: u32, M: u32, S: bool>(x: uN[N], y: xN[S][M][N], z: xN[S][M]) -> xN[S][M];
 
+fn read<T: type>(source: State<T>) -> T;
+
 fn recv_if_non_blocking<T: type>(tok: token, channel: chan<T> in, predicate: bool, value: T) -> (token, T, bool);
 
 fn recv_if<T: type>(tok: token, channel: chan<T> in, predicate: bool, value: T) -> (token, T);
@@ -104,6 +108,8 @@ fn umulp<N: u32>(x: uN[N], y: uN[N]) -> (uN[N], uN[N]);
 
 fn widening_cast<DEST: type, SRC: type>(x: SRC) -> DEST;
 
+fn write<T: type>(dest: State<T>, value: T);
+
 fn xor_reduce<N: u32>(x: uN[N]) -> u1;
 
 fn zip<LHS_TYPE: type, N: u32, RHS_TYPE: type>(lhs: LHS_TYPE[N], rhs: RHS_TYPE[N]) ->
@@ -115,5 +121,3 @@ fn zip<LHS_TYPE: type, N: u32, RHS_TYPE: type>(lhs: LHS_TYPE[N], rhs: RHS_TYPE[N
 trait ToBits {
   fn to_bits(self) -> bits[bit_count<Self>()];
 }
-
-struct State<T: type> {}

xls/dslx/type_system/testdata/type_info_to_proto_test_BitsConstructorTypeProto.txt

@@ -35,4 +35,4 @@
 5:46-5:50: NUMBER :: `true` :: uN[1]
 5:52-5:56: NUMBER :: `true` :: uN[1]
 5:60-5:65: NUMBER :: `false` :: uN[1]
-23:37-23:39: TYPE_ANNOTATION :: `()` :: typeof(())
+25:37-25:39: TYPE_ANNOTATION :: `()` :: typeof(())