From d174d2f65ba34906160e867776a0a5b258ede247 Mon Sep 17 00:00:00 2001
From: Peter Kasting <pkasting@chromium.org>
Date: Sun, 29 Jan 2023 06:32:00 +0000
Subject: [PATCH] Convert base::clamp to std::clamp under the hood.

Bug: 1373621
Change-Id: I1dde975f08c195f50b92a7adc0b497823096ff27
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3946347
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1098352}
---
 base/cxx17_backports.h           | 22 ++++----------------
 base/cxx17_backports_unittest.cc | 35 ++++++++++++++++++++------------
 ui/gfx/skia_color_space_util.cc  |  1 +
 3 files changed, 27 insertions(+), 31 deletions(-)

diff --git a/base/cxx17_backports.h b/base/cxx17_backports.h
index c37e4fdd477a4..bbcce2789d113 100644
--- a/base/cxx17_backports.h
+++ b/base/cxx17_backports.h
@@ -5,27 +5,13 @@
 #ifndef BASE_CXX17_BACKPORTS_H_
 #define BASE_CXX17_BACKPORTS_H_
 
-#include <functional>
-
-#include "base/check.h"
+#include <algorithm>
 
 namespace base {
 
-// C++14 implementation of C++17's std::clamp():
-// https://en.cppreference.com/w/cpp/algorithm/clamp
-// Please note that the C++ spec makes it undefined behavior to call std::clamp
-// with a value of `lo` that compares greater than the value of `hi`. This
-// implementation uses a CHECK to enforce this as a hard restriction.
-template <typename T, typename Compare>
-constexpr const T& clamp(const T& v, const T& lo, const T& hi, Compare comp) {
-  CHECK(!comp(hi, lo));
-  return comp(v, lo) ? lo : comp(hi, v) ? hi : v;
-}
-
-template <typename T>
-constexpr const T& clamp(const T& v, const T& lo, const T& hi) {
-  return base::clamp(v, lo, hi, std::less<T>{});
-}
+// TODO(crbug.com/1373621): Rewrite all uses of base::clamp as std::clamp and
+// remove this file.
+using std::clamp;
 
 }  // namespace base
 
diff --git a/base/cxx17_backports_unittest.cc b/base/cxx17_backports_unittest.cc
index 5e6401a4c7424..c0c73219c45a7 100644
--- a/base/cxx17_backports_unittest.cc
+++ b/base/cxx17_backports_unittest.cc
@@ -4,15 +4,8 @@
 
 #include "base/cxx17_backports.h"
 
-#include <array>
-#include <memory>
 #include <tuple>
-#include <type_traits>
-#include <utility>
-#include <vector>
 
-#include "base/test/gtest_util.h"
-#include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ -38,7 +31,7 @@ bool operator==(const AnotherType& lhs, const AnotherType& rhs) {
   return lhs.some_other_int == rhs.some_other_int;
 }
 
-TEST(Cxx17BackportTest, Clamp) {
+TEST(ClampTest, Behavior) {
   EXPECT_EQ(0, base::clamp(-5, 0, 10));
   EXPECT_EQ(0, base::clamp(0, 0, 10));
   EXPECT_EQ(3, base::clamp(3, 0, 10));
@@ -89,12 +82,28 @@ TEST(Cxx17BackportTest, Clamp) {
   EXPECT_EQ(another_type_10,
             base::clamp(another_type_15, another_type_0, another_type_10,
                         compare_another_type));
+}
+
+TEST(ClampTest, Death) {
+  EXPECT_DEATH_IF_SUPPORTED(std::ignore = base::clamp(3, 10, 0), "");
+  EXPECT_DEATH_IF_SUPPORTED(std::ignore = base::clamp(3.0, 10.0, 0.0), "");
+
+  OneType one_type_0{0};
+  OneType one_type_3{3};
+  OneType one_type_10{10};
+  AnotherType another_type_0{0};
+  AnotherType another_type_3{3};
+  AnotherType another_type_10{10};
+  auto compare_another_type = [](const auto& lhs, const auto& rhs) {
+    return lhs.some_other_int < rhs.some_other_int;
+  };
 
-  EXPECT_CHECK_DEATH(base::clamp(3, 10, 0));
-  EXPECT_CHECK_DEATH(base::clamp(3.0, 10.0, 0.0));
-  EXPECT_CHECK_DEATH(base::clamp(one_type_3, one_type_10, one_type_0));
-  EXPECT_CHECK_DEATH(base::clamp(another_type_3, another_type_10,
-                                 another_type_0, compare_another_type));
+  EXPECT_DEATH_IF_SUPPORTED(
+      std::ignore = base::clamp(one_type_3, one_type_10, one_type_0), "");
+  EXPECT_DEATH_IF_SUPPORTED(
+      std::ignore = base::clamp(another_type_3, another_type_10, another_type_0,
+                                compare_another_type),
+      "");
 }
 
 }  // namespace
diff --git a/ui/gfx/skia_color_space_util.cc b/ui/gfx/skia_color_space_util.cc
index 0bae7399b14d8..ab04f0a094be4 100644
--- a/ui/gfx/skia_color_space_util.cc
+++ b/ui/gfx/skia_color_space_util.cc
@@ -8,6 +8,7 @@
 #include <cmath>
 #include <vector>
 
+#include "base/check.h"
 #include "base/cxx17_backports.h"
 
 namespace gfx {