serde/json/test: add JSONTestSuite parsing conformance suite

Fetch the test_parsing corpus from https://github.com/nst/JSONTestSuite
(MIT, Nicolas Seriot) via a pinned http_archive and run it as a
parameterized gtest. File-name prefixes encode the expected parser
behavior per RFC 8259: y_ must be accepted, n_ must be rejected, i_ is
implementation-defined (the parser just must not crash).

The current parser passes all 318 cases with default config.

get_runfile_path gains an optional repo parameter (default _main) so
callers can resolve data from external Bazel repositories.

Author: nvartolomei

MODULE.bazel

@@ -482,3 +482,20 @@ http_archive(
     strip_prefix = "antithesis-sdk-cpp-0.4.7",
     urls = ["https://github.com/antithesishq/antithesis-sdk-cpp/archive/refs/tags/0.4.7.tar.gz"],
 )
+
+# JSON parser conformance corpus used by
+# //src/v/serde/json/tests:json_test_suite_test. MIT-licensed; see
+# https://github.com/nst/JSONTestSuite.
+http_archive(
+    name = "nst_json_test_suite",
+    build_file_content = """
+filegroup(
+    name = "test_parsing",
+    srcs = glob(["test_parsing/*.json"]),
+    visibility = ["//visibility:public"],
+)
+""",
+    integrity = "sha256-Mqsvs3zCZnnb2RZNu3BTvO8QE0ZD1TywzvRd52gNzcw=",
+    strip_prefix = "JSONTestSuite-1ef36fa01286573e846ac449e8683f8833c5b26a",
+    urls = ["https://github.com/nst/JSONTestSuite/archive/1ef36fa01286573e846ac449e8683f8833c5b26a.tar.gz"],
+)

src/v/serde/json/tests/BUILD

@@ -102,6 +102,27 @@ redpanda_cc_gtest(
     ],
 )
 
+redpanda_cc_gtest(
+    name = "json_test_suite_test",
+    timeout = "short",
+    srcs = [
+        "json_test_suite_test.cc",
+    ],
+    cpu = 1,
+    data = ["@nst_json_test_suite//:test_parsing"],
+    deps = [
+        ":test_cases",
+        "//src/v/bytes:iobuf",
+        "//src/v/serde/json:parser",
+        "//src/v/test_utils:gtest",
+        "//src/v/test_utils:runfiles",
+        "//src/v/utils:file_io",
+        "@googletest//:gtest",
+        "@googletest//:gtest_main",
+        "@seastar",
+    ],
+)
+
 redpanda_test_cc_library(
     name = "data",
     srcs = [

src/v/serde/json/tests/json_test_suite_test.cc

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2026 Redpanda Data, Inc.
+ *
+ * Use of this software is governed by the Business Source License
+ * included in the file licenses/BSL.md
+ *
+ * As of the Change Date specified in that file, in accordance with
+ * the Business Source License, use of this software will be governed
+ * by the Apache License, Version 2.0
+ */
+
+#include "serde/json/parser.h"
+#include "serde/json/tests/test_cases.h"
+#include "test_utils/runfiles.h"
+#include "test_utils/test.h"
+#include "utils/file_io.h"
+
+#include <gtest/gtest.h>
+
+#include <filesystem>
+#include <string>
+
+using namespace serde::json;
+
+/// Test suite from https://github.com/nst/JSONTestSuite.
+///
+/// File-name prefixes encode the expected parser behavior per RFC 8259:
+/// - y_ must be accepted
+/// - n_ must be rejected
+/// - i_ parsers are free to accept or reject
+class json_test_suite_test
+  : public seastar_test
+  , public ::testing::WithParamInterface<std::string> {};
+
+TEST_P_CORO(json_test_suite_test, test_parsing) {
+    const auto& test_case_path = GetParam();
+    auto filename = std::filesystem::path(test_case_path).filename().string();
+
+    auto contents = co_await read_fully(test_case_path);
+    auto parser = serde::json::parser(std::move(contents), parser_config{});
+
+    while (co_await parser.next()) {
+    }
+
+    auto final_token = parser.token();
+    ASSERT_TRUE_CORO(final_token == token::eof || final_token == token::error)
+      << "parser::next() returned false but final token is neither eof nor "
+         "error: "
+      << final_token;
+    bool accepted = final_token == token::eof;
+
+    if (filename.starts_with("y_")) {
+        EXPECT_TRUE(accepted) << filename << ": expected accept, got reject";
+    } else if (filename.starts_with("n_")) {
+        EXPECT_FALSE(accepted) << filename << ": expected reject, got accept";
+    } else {
+        vassert(
+          filename.starts_with("i_"),
+          "Unexpected test case name prefix: {}",
+          filename);
+        // Implementation-defined: either outcome is acceptable. The parser
+        // must not crash.
+    }
+}
+
+INSTANTIATE_TEST_SUITE_P(
+  json_test_suite,
+  json_test_suite_test,
+  ::testing::ValuesIn(
+    serde::json::testing::collect_json_test_cases(
+      test_utils::get_runfile_path("test_parsing", "nst_json_test_suite"))),
+  [](const ::testing::TestParamInfo<std::string>& info) {
+      // GTest requires parameter names to match [a-zA-Z0-9_] and to be
+      // unique. Use the filename stem and hex-escape any non-alphanumeric
+      // chars (using `_XX`) to preserve uniqueness across similar names.
+      auto stem = std::filesystem::path(info.param).stem().string();
+      std::string out;
+      out.reserve(stem.size());
+      for (auto c : stem) {
+          auto uc = static_cast<unsigned char>(c);
+          if (std::isalnum(uc) || uc == '_') {
+              out.push_back(c);
+          } else {
+              fmt::format_to(std::back_inserter(out), "_{:02x}", uc);
+          }
+      }
+      return out;
+  });

src/v/test_utils/runfiles.cc

@@ -10,7 +10,7 @@
 
 namespace test_utils {
 
-std::string get_runfile_path(std::string_view path) {
+std::string get_runfile_path(std::string_view path, std::string_view repo) {
     using bazel::tools::cpp::runfiles::Runfiles;
     std::string error;
     std::unique_ptr<Runfiles> runfiles;
@@ -25,7 +25,7 @@ std::string get_runfile_path(std::string_view path) {
     if (runfiles == nullptr) {
         throw std::runtime_error(error);
     }
-    return runfiles->Rlocation(fmt::format("_main/{}", path));
+    return runfiles->Rlocation(fmt::format("{}/{}", repo, path));
 }
 
 } // namespace test_utils

src/v/test_utils/runfiles.h

@@ -6,12 +6,19 @@
 namespace test_utils {
 
 /*
- * Usage:
- *  - Add a `data = [path/to/some.file]` to the test target
- *  - Call get_runfile_path with "root/.../path/to/some.file"
+ * Resolve `path` to an absolute filesystem path at test runtime.
  *
- * The return value is the path to the file.
+ * `path` is a repo-relative path (e.g. "src/v/.../testdata/foo.json" for
+ * files from this repository). The file must be listed in the test
+ * target's `data = [...]` attribute so Bazel stages it into the
+ * runfiles tree.
+ *
+ * `repo` selects which Bazel repository the path is rooted in. It
+ * defaults to "_main" (this repository). For files exposed by an
+ * external repository — e.g. a `http_archive` declared in MODULE.bazel —
+ * pass that repository's name.
  */
-std::string get_runfile_path(std::string_view);
+std::string
+get_runfile_path(std::string_view path, std::string_view repo = "_main");
 
 } // namespace test_utils