Adds a time zone fuzz test

Based on
https://github.com/google/oss-fuzz/blob/master/projects/cctz/fuzz_cctz.cc
but uses the Google FuzzTest framework and runs directly in the CCTZ
project using Bazel

Author: derekmauro

.github/workflows/ci.yaml

@@ -19,6 +19,7 @@ jobs:
     - name: Tests
       run: >
         bazel test ...
+        --build_tag_filters=-fuzztest
         --copt=-DGTEST_REMOVE_LEGACY_TEST_CASEAPI_=1
         --copt=-Werror
         --cxxopt=-Wall
@@ -43,7 +44,7 @@ jobs:
         --show_timestamps
         --test_env="TZDIR=${GITHUB_WORKSPACE}/testdata/zoneinfo"
         --test_output=errors
-        --test_tag_filters=-benchmark
+        --test_tag_filters=-benchmark,-fuzztest
 
   Linux-Clang:
     runs-on: ubuntu-latest
@@ -99,6 +100,32 @@ jobs:
         --test_output=errors
         --test_tag_filters=-benchmark
 
+  Linux-FuzzTest:
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - name: Configure Fuzztest
+      run: bazel run @fuzztest//bazel:setup_configs > fuzztest.bazelrc
+    - name: Fuzz
+      run: >
+        bazel --bazelrc=fuzztest.bazelrc test ...
+        --action_env=CC=clang
+        --build_tag_filters=fuzztest
+        --config=fuzztest
+        --copt=-DGTEST_REMOVE_LEGACY_TEST_CASEAPI_=1
+        --define=absl=1
+        --features=external_include_paths
+        --keep_going
+        --show_timestamps
+        --test_arg=--fuzz_for=30s
+        --test_env="TZDIR=${GITHUB_WORKSPACE}/testdata/zoneinfo"
+        --test_output=errors
+        --test_tag_filters=fuzztest
+
   macOS:
     runs-on: macos-latest
     steps:
@@ -110,13 +137,14 @@ jobs:
     - name: Tests
       run: >
         bazel test ...
+        --build_tag_filters=-fuzztest
         --cxxopt="-std=c++17"
         --features=external_include_paths
         --keep_going
         --show_timestamps
         --test_env="TZDIR=${GITHUB_WORKSPACE}/testdata/zoneinfo"
         --test_output=errors
-        --test_tag_filters=-benchmark
+        --test_tag_filters=-benchmark,-fuzztest
 
   Windows:
     runs-on: windows-latest
@@ -129,8 +157,9 @@ jobs:
     - name: Tests
       run: >
         bazel test ...
+        --build_tag_filters=-fuzztest
         --keep_going
         --show_timestamps
         --test_env="TZDIR=$env:GITHUB_WORKSPACE\testdata\zoneinfo"
         --test_output=errors
-        --test_tag_filters=-benchmark
+        --test_tag_filters=-benchmark,-fuzztest

BUILD

@@ -75,9 +75,12 @@ cc_library(
 
 ### tests
 
-test_suite(
-    name = "all_tests",
-    visibility = ["//visibility:public"],
+cc_library(
+    name = "time_zone_test_util",
+    testonly = True,
+    srcs = ["src/time_zone_test_util.cc"],
+    hdrs = ["src/time_zone_test_util.h"],
+    visibility = ["//visibility:private"],
 )
 
 cc_test(
@@ -110,11 +113,34 @@ cc_test(
     deps = [
         ":civil_time",
         ":time_zone",
+        ":time_zone_test_util",
         "@googletest//:gtest",
         "@googletest//:gtest_main",
     ],
 )
 
+cc_test(
+    name = "time_zone_fuzz_test",
+    srcs = [
+        "src/time_zone_fuzz_test.cc",
+        "src/time_zone_if.h",
+        "src/time_zone_impl.h",
+        "src/time_zone_info.h",
+        "src/tzfile.h",
+    ],
+    tags = [
+        "fuzztest",
+    ],
+    deps = [
+        ":civil_time",
+        ":time_zone",
+        ":time_zone_test_util",
+        "@fuzztest//fuzztest",
+        "@fuzztest//fuzztest:fuzztest_gtest_main",
+        "@googletest//:gtest",
+    ],
+)
+
 ### benchmarks
 
 cc_test(

CMakeLists.txt

@@ -111,6 +111,11 @@ if (BUILD_EXAMPLES)
 endif()
 
 if (BUILD_TESTING)
+  add_library(time_zone_test_util
+    "src/time_zone_test_util.cc"
+    "src/time_zone_test_util.h"
+    )
+
   add_executable(civil_time_test src/civil_time_test.cc)
   cctz_target_set_cxx_standard(civil_time_test)
   target_include_directories(civil_time_test PRIVATE ${GTEST_INCLUDE_DIRS})
@@ -126,6 +131,7 @@ if (BUILD_TESTING)
   target_include_directories(time_zone_lookup_test PRIVATE ${GTEST_INCLUDE_DIRS})
   target_link_libraries(time_zone_lookup_test
     cctz::cctz
+    time_zone_test_util
     ${GTEST_BOTH_LIBRARIES}
     ${CMAKE_THREAD_LIBS_INIT}
     )

MODULE.bazel

@@ -22,6 +22,10 @@ module(
 
 # Only direct dependencies need to be listed below.
 
+bazel_dep(name = "fuzztest",
+          version = "20250728.0",
+          dev_dependency = True)
+
 bazel_dep(name = "google_benchmark",
           version = "1.9.4",
           dev_dependency = True)

src/time_zone_fuzz_test.cc

@@ -0,0 +1,76 @@
+// Copyright 2025 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+
+#include <cstdint>
+#include <cstdlib>
+#include <limits>
+#include <string>
+#include <vector>
+
+#include "cctz/civil_time.h"
+#include "cctz/time_zone.h"
+#include "fuzztest/fuzztest.h"
+#include "gtest/gtest.h"
+#include "time_zone_impl.h"
+#include "time_zone_test_util.h"
+
+namespace cctz {
+
+namespace {
+
+std::vector<std::string> TimeZoneSeeds() {
+  std::vector<std::string> time_zone_seeds;
+  for (const char* const* tzptr = kTimeZoneNames; *tzptr != nullptr; ++tzptr) {
+    time_zone_seeds.push_back(*tzptr);
+  }
+  return time_zone_seeds;
+}
+
+void Fuzz(const std::string& time_zone_name, const std::int64_t year,
+          const std::int64_t month, const std::int64_t day,
+          const std::int64_t hour, const std::int64_t minute,
+          const std::int64_t second, const std::string& format_string,
+          const std::string& cctz_parse_input) {
+  cctz::time_zone time_zone;
+  if (!cctz::load_time_zone(time_zone_name, &time_zone)) {
+    return;
+  }
+  const cctz::civil_second cs(year, month, day, hour, minute, second);
+  auto time_point = cctz::convert(cs, time_zone);
+  cctz::format(format_string, time_point, time_zone);
+  cctz::time_point<cctz::seconds> parsed_time_point;
+  cctz::parse(format_string, cctz_parse_input, time_zone, &parsed_time_point);
+  auto repeated_time_point = cctz::convert(cs, time_zone);
+  EXPECT_EQ(time_point, repeated_time_point);
+}
+
+FUZZ_TEST(TimeZoneFuzzTest, Fuzz)
+    .WithDomains(fuzztest::Arbitrary<std::string>().WithSeeds(TimeZoneSeeds()),
+                 // We limit the search-space for years to avoid expected
+                 // undefined behavior that may occur when normalizing a civil
+                 // second outside the 64-bit representable year range.
+                 fuzztest::InRange(std::numeric_limits<std::int64_t>::min() / 2,
+                                   std::numeric_limits<std::int64_t>::max() /
+                                       2),             // year
+                 fuzztest::Arbitrary<std::int64_t>(),  // month
+                 fuzztest::Arbitrary<std::int64_t>(),  // day
+                 fuzztest::Arbitrary<std::int64_t>(),  // hour
+                 fuzztest::Arbitrary<std::int64_t>(),  // minute
+                 fuzztest::Arbitrary<std::int64_t>(),  // second
+                 fuzztest::Arbitrary<std::string>(),   // format_string
+                 fuzztest::Arbitrary<std::string>());  // cctz_parse_input
+
+}  // namespace
+
+}  // namespace cctz