Add a unit test that captures the current behavior of formatting of char types and char-backed enum types through StrCat(), StrFormat("%v"), and Substitute().

This test allows us to modify the behavior in this space without introducing undesired changes elsewhere.

PiperOrigin-RevId: 537981963
Change-Id: Icda91b66efcc0dc8c263011b137e130a3db2dc19

absl/strings/BUILD.bazel

@@ -1319,3 +1319,15 @@ cc_binary(
         "//absl/types:optional",
     ],
 )
+
+cc_test(
+    name = "char_formatting_test",
+    srcs = [
+        "char_formatting_test.cc",
+    ],
+    deps = [
+        ":str_format",
+        ":strings",
+        "@com_google_googletest//:gtest_main",
+    ],
+)

absl/strings/CMakeLists.txt

@@ -548,6 +548,20 @@ absl_cc_test(
     GTest::gmock_main
 )
 
+absl_cc_test(
+  NAME
+    char_formatting_test
+  SRCS
+    "char_formatting_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::base
+    absl::str_format
+    absl::strings
+    GTest::gmock_main
+)
+
 # Internal-only target, do not depend on directly.
 absl_cc_library(
   NAME

absl/strings/char_formatting_test.cc

@@ -0,0 +1,189 @@
+// Copyright 2023 The Abseil Authors
+//
+// 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
+//
+//     https://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 <cstddef>
+
+#include "gtest/gtest.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_format.h"
+#include "absl/strings/substitute.h"
+
+namespace {
+
+TEST(CharFormatting, Char) {
+  const char v = 'A';
+
+  // Desired behavior: does not compile:
+  // EXPECT_EQ(absl::StrCat(v, "B"), "AB");
+  // EXPECT_EQ(absl::StrFormat("%vB", v), "AB");
+
+  // Legacy behavior: format as char:
+  EXPECT_EQ(absl::Substitute("$0B", v), "AB");
+}
+
+enum CharEnum : char {};
+TEST(CharFormatting, CharEnum) {
+  auto v = static_cast<CharEnum>('A');
+
+  // Desired behavior: format as decimal
+  // (No APIs do this today.)
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Legacy behavior: does not compile:
+  // EXPECT_EQ(absl::StrCat(ch, "B"), "AB");
+
+  // Legacy behavior: format as character:
+
+  // Some older versions of gcc behave differently in this one case.
+#if !defined(__GNUC__) || defined(__clang__)
+  EXPECT_EQ(absl::Substitute("$0B", v), "AB");
+#endif
+}
+
+enum class CharEnumClass: char {};
+TEST(CharFormatting, CharEnumClass) {
+  auto v = static_cast<CharEnumClass>('A');
+
+  // Desired behavior: format as decimal
+  // (No APIs do this today.)
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Legacy behavior: does not compile:
+  // EXPECT_EQ(absl::StrCat(ch, "B"), "AB");
+
+  // Legacy behavior: format as character:
+  EXPECT_EQ(absl::Substitute("$0B", v), "AB");
+}
+
+TEST(CharFormatting, UnsignedChar) {
+  const unsigned char v = 'A';
+
+  // Desired behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+
+  // Legacy behavior: does not compile:
+  // EXPECT_EQ(absl::StrFormat("%vB", v), "65B");
+
+  // Signedness check
+  const unsigned char w = 255;
+  EXPECT_EQ(absl::StrCat(w, "B"), "255B");
+  EXPECT_EQ(absl::Substitute("$0B", w), "255B");
+  // EXPECT_EQ(absl::StrFormat("%vB", v), "255B");
+}
+
+TEST(CharFormatting, SignedChar) {
+  const signed char v = 'A';
+
+  // Desired behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+
+  // Legacy behavior: does not compile:
+  // EXPECT_EQ(absl::StrFormat("%vB", v), "AB");
+
+  // Signedness check
+  const signed char w = -128;
+  EXPECT_EQ(absl::StrCat(w, "B"), "-128B");
+  EXPECT_EQ(absl::Substitute("$0B", w), "-128B");
+}
+
+enum UnsignedCharEnum : unsigned char {};
+TEST(CharFormatting, UnsignedCharEnum) {
+  auto v = static_cast<UnsignedCharEnum>('A');
+
+  // Desired behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Signedness check
+  auto w = static_cast<UnsignedCharEnum>(255);
+  EXPECT_EQ(absl::StrCat(w, "B"), "255B");
+  EXPECT_EQ(absl::Substitute("$0B", w), "255B");
+}
+
+enum SignedCharEnum : signed char {};
+TEST(CharFormatting, SignedCharEnum) {
+  auto v = static_cast<SignedCharEnum>('A');
+
+  // Desired behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Signedness check
+  auto w = static_cast<SignedCharEnum>(-128);
+  EXPECT_EQ(absl::StrCat(w, "B"), "-128B");
+  EXPECT_EQ(absl::Substitute("$0B", w), "-128B");
+}
+
+enum class UnsignedCharEnumClass : unsigned char {};
+TEST(CharFormatting, UnsignedCharEnumClass) {
+  auto v = static_cast<UnsignedCharEnumClass>('A');
+
+  // Desired behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Signedness check
+  auto w = static_cast<UnsignedCharEnumClass>(255);
+  EXPECT_EQ(absl::StrCat(w, "B"), "255B");
+  EXPECT_EQ(absl::Substitute("$0B", w), "255B");
+}
+
+enum SignedCharEnumClass : signed char {};
+TEST(CharFormatting, SignedCharEnumClass) {
+  auto v = static_cast<SignedCharEnumClass>('A');
+
+  // Desired behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Signedness check
+  auto w = static_cast<SignedCharEnumClass>(-128);
+  EXPECT_EQ(absl::StrCat(w, "B"), "-128B");
+  EXPECT_EQ(absl::Substitute("$0B", w), "-128B");
+}
+
+#ifdef __cpp_lib_byte
+TEST(CharFormatting, StdByte) {
+  auto v = static_cast<std::byte>('A');
+  // Desired behavior: format as 0xff
+  // (No APIs do this today.)
+
+  // BUG: internally fails
+  EXPECT_EQ(absl::StrFormat("%vB", v), "");
+
+  // Legacy behavior: format as decimal:
+  EXPECT_EQ(absl::StrCat(v, "B"), "65B");
+  EXPECT_EQ(absl::Substitute("$0B", v), "65B");
+}
+#endif  // _cpp_lib_byte
+
+}  // namespace