Forbid absl::Uniform<absl::int128>(gen)

std::is_signed can't be specialized, so this actually lets through non-unsigned types where the types are not language primitives (i.e. it lets absl::int128 through). However, std::numeric_limits can be specialized, and is indeed specialized, so we can use that instead.
PiperOrigin-RevId: 636983590
Change-Id: Ic993518e9cac7c453b08deaf3784b6fba49f15d0

absl/random/BUILD.bazel

@@ -221,6 +221,8 @@ cc_test(
     deps = [
         ":distributions",
         ":random",
+        "//absl/meta:type_traits",
+        "//absl/numeric:int128",
         "//absl/random/internal:distribution_test_util",
         "@com_google_googletest//:gtest",
         "@com_google_googletest//:gtest_main",

absl/random/CMakeLists.txt

@@ -288,6 +288,8 @@ absl_cc_test(
   DEPS
     absl::random_distributions
     absl::random_random
+    absl::type_traits
+    absl::int128
     absl::random_internal_distribution_test_util
     GTest::gmock
     GTest::gtest_main

absl/random/distributions.h

@@ -46,23 +46,23 @@
 #ifndef ABSL_RANDOM_DISTRIBUTIONS_H_
 #define ABSL_RANDOM_DISTRIBUTIONS_H_
 
-#include <algorithm>
-#include <cmath>
 #include <limits>
-#include <random>
 #include <type_traits>
 
+#include "absl/base/config.h"
 #include "absl/base/internal/inline_variable.h"
+#include "absl/meta/type_traits.h"
 #include "absl/random/bernoulli_distribution.h"
 #include "absl/random/beta_distribution.h"
 #include "absl/random/exponential_distribution.h"
 #include "absl/random/gaussian_distribution.h"
 #include "absl/random/internal/distribution_caller.h"  // IWYU pragma: export
+#include "absl/random/internal/traits.h"
 #include "absl/random/internal/uniform_helper.h"  // IWYU pragma: export
 #include "absl/random/log_uniform_int_distribution.h"
 #include "absl/random/poisson_distribution.h"
-#include "absl/random/uniform_int_distribution.h"
-#include "absl/random/uniform_real_distribution.h"
+#include "absl/random/uniform_int_distribution.h"  // IWYU pragma: export
+#include "absl/random/uniform_real_distribution.h"  // IWYU pragma: export
 #include "absl/random/zipf_distribution.h"
 
 namespace absl {
@@ -208,7 +208,7 @@ Uniform(URBG&& urbg,  // NOLINT(runtime/references)
 // Overload of Uniform() using the minimum and maximum values of a given type
 // `T` (which must be unsigned), returning a value of type `unsigned T`
 template <typename R, typename URBG>
-typename absl::enable_if_t<!std::is_signed<R>::value, R>  //
+typename absl::enable_if_t<!std::numeric_limits<R>::is_signed, R>  //
 Uniform(URBG&& urbg) {  // NOLINT(runtime/references)
   using gen_t = absl::decay_t<URBG>;
   using distribution_t = random_internal::UniformDistributionWrapper<R>;

absl/random/distributions_test.cc

@@ -17,10 +17,14 @@
 #include <cfloat>
 #include <cmath>
 #include <cstdint>
-#include <random>
+#include <limits>
+#include <type_traits>
+#include <utility>
 #include <vector>
 
 #include "gtest/gtest.h"
+#include "absl/meta/type_traits.h"
+#include "absl/numeric/int128.h"
 #include "absl/random/internal/distribution_test_util.h"
 #include "absl/random/random.h"
 
@@ -30,7 +34,6 @@ constexpr int kSize = 400000;
 
 class RandomDistributionsTest : public testing::Test {};
 
-
 struct Invalid {};
 
 template <typename A, typename B>
@@ -93,16 +96,17 @@ void CheckArgsInferType() {
 }
 
 template <typename A, typename B, typename ExplicitRet>
-auto ExplicitUniformReturnT(int) -> decltype(
-    absl::Uniform<ExplicitRet>(*std::declval<absl::InsecureBitGen*>(),
+auto ExplicitUniformReturnT(int) -> decltype(absl::Uniform<ExplicitRet>(
+                                     std::declval<absl::InsecureBitGen&>(),
                                      std::declval<A>(), std::declval<B>()));
 
 template <typename, typename, typename ExplicitRet>
 Invalid ExplicitUniformReturnT(...);
 
 template <typename TagType, typename A, typename B, typename ExplicitRet>
-auto ExplicitTaggedUniformReturnT(int) -> decltype(absl::Uniform<ExplicitRet>(
-    std::declval<TagType>(), *std::declval<absl::InsecureBitGen*>(),
+auto ExplicitTaggedUniformReturnT(int)
+    -> decltype(absl::Uniform<ExplicitRet>(
+        std::declval<TagType>(), std::declval<absl::InsecureBitGen&>(),
         std::declval<A>(), std::declval<B>()));
 
 template <typename, typename, typename, typename ExplicitRet>
@@ -135,6 +139,14 @@ void CheckArgsReturnExpectedType() {
       "");
 }
 
+// Takes the type of `absl::Uniform<R>(gen)` if valid or `Invalid` otherwise.
+template <typename R>
+auto UniformNoBoundsReturnT(int)
+    -> decltype(absl::Uniform<R>(std::declval<absl::InsecureBitGen&>()));
+
+template <typename>
+Invalid UniformNoBoundsReturnT(...);
+
 TEST_F(RandomDistributionsTest, UniformTypeInference) {
   // Infers common types.
   CheckArgsInferType<uint16_t, uint16_t, uint16_t>();
@@ -221,6 +233,38 @@ TEST_F(RandomDistributionsTest, UniformNoBounds) {
   absl::Uniform<uint32_t>(gen);
   absl::Uniform<uint64_t>(gen);
   absl::Uniform<absl::uint128>(gen);
+
+  // Compile-time validity tests.
+
+  // Allows unsigned ints.
+  testing::StaticAssertTypeEq<uint8_t,
+                              decltype(UniformNoBoundsReturnT<uint8_t>(0))>();
+  testing::StaticAssertTypeEq<uint16_t,
+                              decltype(UniformNoBoundsReturnT<uint16_t>(0))>();
+  testing::StaticAssertTypeEq<uint32_t,
+                              decltype(UniformNoBoundsReturnT<uint32_t>(0))>();
+  testing::StaticAssertTypeEq<uint64_t,
+                              decltype(UniformNoBoundsReturnT<uint64_t>(0))>();
+  testing::StaticAssertTypeEq<
+      absl::uint128, decltype(UniformNoBoundsReturnT<absl::uint128>(0))>();
+
+  // Disallows signed ints.
+  testing::StaticAssertTypeEq<Invalid,
+                              decltype(UniformNoBoundsReturnT<int8_t>(0))>();
+  testing::StaticAssertTypeEq<Invalid,
+                              decltype(UniformNoBoundsReturnT<int16_t>(0))>();
+  testing::StaticAssertTypeEq<Invalid,
+                              decltype(UniformNoBoundsReturnT<int32_t>(0))>();
+  testing::StaticAssertTypeEq<Invalid,
+                              decltype(UniformNoBoundsReturnT<int64_t>(0))>();
+  testing::StaticAssertTypeEq<
+      Invalid, decltype(UniformNoBoundsReturnT<absl::int128>(0))>();
+
+  // Disallows float types.
+  testing::StaticAssertTypeEq<Invalid,
+                              decltype(UniformNoBoundsReturnT<float>(0))>();
+  testing::StaticAssertTypeEq<Invalid,
+                              decltype(UniformNoBoundsReturnT<double>(0))>();
 }
 
 TEST_F(RandomDistributionsTest, UniformNonsenseRanges) {