[DSLX:fmt] Add support for zero! macro construct.

PiperOrigin-RevId: 572722446

xls/dslx/fmt/BUILD

@@ -72,6 +72,7 @@ cc_test(
     deps = [
         ":ast_fmt",
         ":pretty_print",
+        "@com_google_absl//absl/container:flat_hash_set",
         "@com_google_absl//absl/status:statusor",
         "//xls/common:xls_gunit",
         "//xls/common:xls_gunit_main",

xls/dslx/fmt/ast_fmt.cc

@@ -717,7 +717,14 @@ DocRef Fmt(const UnrollFor& n, const Comments& comments, DocArena& arena) {
 }
 
 DocRef Fmt(const ZeroMacro& n, const Comments& comments, DocArena& arena) {
-  XLS_LOG(FATAL) << "handle zero macro: " << n.ToString();
+  return ConcatNGroup(arena, {
+                                 arena.MakeText("zero!"),
+                                 arena.oangle(),
+                                 FmtExprOrType(n.type(), comments, arena),
+                                 arena.cangle(),
+                                 arena.oparen(),
+                                 arena.cparen(),
+                             });
 }
 
 DocRef Fmt(const Unop& n, const Comments& comments, DocArena& arena) {

xls/dslx/fmt/ast_fmt_test.cc

@@ -20,6 +20,7 @@
 #include <vector>
 
 #include "gtest/gtest.h"
+#include "absl/container/flat_hash_set.h"
 #include "absl/status/statusor.h"
 #include "xls/common/logging/logging.h"
 #include "xls/common/status/matchers.h"
@@ -123,10 +124,20 @@ let x: u32 = u32:42)");
 // Use `ModuleFmtTest` for formatting of entire modules.
 class FunctionFmtTest : public testing::Test {
  public:
-  absl::StatusOr<std::string> DoFmt(std::string_view original) {
+  // Args:
+  //  original: The text to parse-then-auto-format.
+  //  builtin_name_defs: Names to initialize in the bindings as built-in.
+  absl::StatusOr<std::string> DoFmt(
+      std::string_view original,
+      const absl::flat_hash_set<std::string>& builtin_name_defs = {}) {
     XLS_CHECK(!scanner_.has_value());
     scanner_.emplace("fake.x", std::string{original});
     parser_.emplace("fake", &scanner_.value());
+
+    for (const std::string& name : builtin_name_defs) {
+      bindings_.Add(name, parser_->module().GetOrCreateBuiltinNameDef(name));
+    }
+
     XLS_ASSIGN_OR_RETURN(
         f_, parser_->ParseFunction(/*is_public=*/false, bindings_));
     Comments comments = Comments::Create(scanner_->comments());
@@ -135,6 +146,8 @@ class FunctionFmtTest : public testing::Test {
     return PrettyPrint(arena_, doc, /*text_width=*/100);
   }
 
+  Bindings& bindings() { return bindings_; }
+
  private:
   DocArena arena_;
   std::optional<Scanner> scanner_;
@@ -377,6 +390,13 @@ TEST_F(FunctionFmtTest, MatchMultiPattern) {
   EXPECT_EQ(got, want);
 }
 
+TEST_F(FunctionFmtTest, ZeroMacro) {
+  const std::string_view original = "fn f()->u32{zero!<u32>()}";
+  XLS_ASSERT_OK_AND_ASSIGN(std::string got, DoFmt(original, {"zero!"}));
+  const std::string_view want = R"(fn f() -> u32 { zero!<u32>() })";
+  EXPECT_EQ(got, want);
+}
+
 // -- ModuleFmtTest cases, formatting entire modules
 
 TEST(ModuleFmtTest, TwoSimpleFunctions) {