Adds support for "%v" in absl::StrFormat and related functions for string-like types (support for other builtin types will follow in future changes). Rather than specifying %s for strings, users may specify %v and have the format specifier deduced. Notably, %v does not work for `const char*` because we cannot be certain if %s or %p was intended (nor can we be certain if the `const char*` was properly null-terminated). If you have a `const char*` you know is null-terminated and would like to work with %v, please wrap it in a `string_view` before using it.

PiperOrigin-RevId: 471321055
Change-Id: Ifbb50082d301baecc7edc277975f12e7ad3ecc8a

7 files changed, 219 insertions, 10 deletions

diff --git a/absl/strings/internal/str_format/arg.h b/absl/strings/internal/str_format/arg.h
index b9dda909..a56ca301 100644
--- a/absl/strings/internal/str_format/arg.h
+++ b/absl/strings/internal/str_format/arg.h
@@ -110,8 +110,8 @@ constexpr FormatConversionCharSet ExtractCharSet(ArgConvertResult<C>) {
   return C;
 }
 
-using StringConvertResult =
-    ArgConvertResult<FormatConversionCharSetInternal::s>;
+using StringConvertResult = ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::s, FormatConversionCharSetInternal::v)>;
 ArgConvertResult<FormatConversionCharSetInternal::p> FormatConvertImpl(
     VoidPtr v, FormatConversionSpecImpl conv, FormatSinkImpl* sink);
 
diff --git a/absl/strings/internal/str_format/bind.h b/absl/strings/internal/str_format/bind.h
index 80f29654..b73c5028 100644
--- a/absl/strings/internal/str_format/bind.h
+++ b/absl/strings/internal/str_format/bind.h
@@ -235,9 +235,10 @@ class StreamedWrapper {
 
  private:
   template <typename S>
-  friend ArgConvertResult<FormatConversionCharSetInternal::s> FormatConvertImpl(
-      const StreamedWrapper<S>& v, FormatConversionSpecImpl conv,
-      FormatSinkImpl* out);
+  friend ArgConvertResult<FormatConversionCharSetUnion(
+      FormatConversionCharSetInternal::s, FormatConversionCharSetInternal::v)>
+  FormatConvertImpl(const StreamedWrapper<S>& v, FormatConversionSpecImpl conv,
+                    FormatSinkImpl* out);
   const T& v_;
 };
 
diff --git a/absl/strings/internal/str_format/checker_test.cc b/absl/strings/internal/str_format/checker_test.cc
index 7c70f47d..b186e7d8 100644
--- a/absl/strings/internal/str_format/checker_test.cc
+++ b/absl/strings/internal/str_format/checker_test.cc
@@ -39,7 +39,7 @@ std::string ConvToString(FormatConversionCharSet conv) {
 
 TEST(StrFormatChecker, ArgumentToConv) {
   FormatConversionCharSet conv = ArgumentToConv<std::string>();
-  EXPECT_EQ(ConvToString(conv), "s");
+  EXPECT_EQ(ConvToString(conv), "sv");
 
   conv = ArgumentToConv<const char*>();
   EXPECT_EQ(ConvToString(conv), "sp");
diff --git a/absl/strings/internal/str_format/extension.h b/absl/strings/internal/str_format/extension.h
index 55e8ac88..f8d98bf7 100644
--- a/absl/strings/internal/str_format/extension.h
+++ b/absl/strings/internal/str_format/extension.h
@@ -169,7 +169,7 @@ inline std::ostream& operator<<(std::ostream& os, Flags v) {
   X_VAL(f) X_SEP X_VAL(F) X_SEP X_VAL(e) X_SEP X_VAL(E) X_SEP \
   X_VAL(g) X_SEP X_VAL(G) X_SEP X_VAL(a) X_SEP X_VAL(A) X_SEP \
   /* misc */ \
-  X_VAL(n) X_SEP X_VAL(p)
+  X_VAL(n) X_SEP X_VAL(p) X_SEP X_VAL(v)
 // clang-format on
 
 // This type should not be referenced, it exists only to provide labels
@@ -191,7 +191,7 @@ struct FormatConversionCharInternal {
     c, s,                    // text
     d, i, o, u, x, X,        // int
     f, F, e, E, g, G, a, A,  // float
-    n, p,                    // misc
+    n, p, v,                    // misc
     kNone
   };
   // clang-format on
diff --git a/absl/strings/internal/str_format/parser.cc b/absl/strings/internal/str_format/parser.cc
index 2c9c07da..3d987334 100644
--- a/absl/strings/internal/str_format/parser.cc
+++ b/absl/strings/internal/str_format/parser.cc
@@ -56,7 +56,7 @@ ABSL_CONST_INIT const ConvTag kTags[256] = {
     CC::X,  {},    {},    {},    {},    {},     {},    {},     // XYZ[\]^_
     {},     CC::a, {},    CC::c, CC::d, CC::e,  CC::f, CC::g,  // `abcdefg
     LM::h,  CC::i, LM::j, {},    LM::l, {},     CC::n, CC::o,  // hijklmno
-    CC::p,  LM::q, {},    CC::s, LM::t, CC::u,  {},    {},     // pqrstuvw
+    CC::p,  LM::q, {},    CC::s, LM::t, CC::u,  CC::v, {},     // pqrstuvw
     CC::x,  {},    LM::z, {},    {},    {},     {},    {},     // xyz{|}!
     {},     {},    {},    {},    {},    {},     {},    {},     // 80-87
     {},     {},    {},    {},    {},    {},     {},    {},     // 88-8f
diff --git a/absl/strings/str_format.h b/absl/strings/str_format.h
index 4b05c70c..e6537ea0 100644
--- a/absl/strings/str_format.h
+++ b/absl/strings/str_format.h
@@ -637,7 +637,7 @@ enum class FormatConversionChar : uint8_t {
   c, s,                    // text
   d, i, o, u, x, X,        // int
   f, F, e, E, g, G, a, A,  // float
-  n, p                     // misc
+  n, p, v                  // misc
 };
 // clang-format on
 
@@ -757,6 +757,7 @@ enum class FormatConversionCharSet : uint64_t {
   // misc
   n = str_format_internal::FormatConversionCharToConvInt('n'),
   p = str_format_internal::FormatConversionCharToConvInt('p'),
+  v = str_format_internal::FormatConversionCharToConvInt('v'),
 
   // Used for width/precision '*' specification.
   kStar = static_cast<uint64_t>(
diff --git a/absl/strings/str_format_test.cc b/absl/strings/str_format_test.cc
index 804e6c22..7bffbb7a 100644
--- a/absl/strings/str_format_test.cc
+++ b/absl/strings/str_format_test.cc
@@ -84,6 +84,11 @@ TEST_F(FormatEntryPointTest, StringFormat) {
   EXPECT_EQ("=123=", StrFormat(view, 123));
 }
 
+TEST_F(FormatEntryPointTest, StringFormatV) {
+  std::string hello = "hello";
+  EXPECT_EQ("hello", StrFormat("%v", hello));
+}
+
 TEST_F(FormatEntryPointTest, AppendFormat) {
   std::string s;
   std::string& r = StrAppendFormat(&s, "%d", 123);
@@ -165,6 +170,21 @@ TEST_F(FormatEntryPointTest, FormatCountCaptureExample) {
       s);
 }
 
+TEST_F(FormatEntryPointTest, FormatCountCaptureExampleWithV) {
+  int n;
+  std::string s;
+  std::string a1 = "(1,1)";
+  std::string a2 = "(1,2)";
+  std::string a3 = "(2,2)";
+  StrAppendFormat(&s, "%v: %n%v\n", a1, FormatCountCapture(&n), a2);
+  StrAppendFormat(&s, "%*s%v\n", n, "", a3);
+  EXPECT_EQ(7, n);
+  EXPECT_EQ(
+      "(1,1): (1,2)\n"
+      "       (2,2)\n",
+      s);
+}
+
 TEST_F(FormatEntryPointTest, Stream) {
   const std::string formats[] = {
     "",
@@ -191,6 +211,26 @@ TEST_F(FormatEntryPointTest, Stream) {
   }
 }
 
+TEST_F(FormatEntryPointTest, StreamWithV) {
+  const std::string format = "%d %u %c %v %f %g";
+
+  const std::string format_for_buf = "%d %u %c %s %f %g";
+
+  std::string buf(4096, '\0');
+  const auto parsed =
+      ParsedFormat<'d', 'u', 'c', 'v', 'f', 'g'>::NewAllowIgnored(format);
+  std::ostringstream oss;
+  oss << StreamFormat(*parsed, 123, 3, 49,
+                      absl::string_view("multistreaming!!!"), 1.01, 1.01);
+  int fmt_result =
+      snprintf(&*buf.begin(), buf.size(), format_for_buf.c_str(),  //
+               123, 3, 49, "multistreaming!!!", 1.01, 1.01);
+  ASSERT_TRUE(oss) << format;
+  ASSERT_TRUE(fmt_result >= 0 && static_cast<size_t>(fmt_result) < buf.size())
+      << fmt_result;
+  EXPECT_EQ(buf.c_str(), oss.str());
+}
+
 TEST_F(FormatEntryPointTest, StreamOk) {
   std::ostringstream oss;
   oss << StreamFormat("hello %d", 123);
@@ -249,6 +289,14 @@ TEST_F(FormatEntryPointTest, FormatStreamed) {
   EXPECT_EQ("123", StrFormat("%s", FormatStreamed(StreamFormat("%d", 123))));
 }
 
+TEST_F(FormatEntryPointTest, FormatStreamedWithV) {
+  EXPECT_EQ("123", StrFormat("%v", FormatStreamed(123)));
+  EXPECT_EQ("  123", StrFormat("%5v", FormatStreamed(123)));
+  EXPECT_EQ("123  ", StrFormat("%-5v", FormatStreamed(123)));
+  EXPECT_EQ("X", StrFormat("%v", FormatStreamed(streamed_test::X())));
+  EXPECT_EQ("123", StrFormat("%v", FormatStreamed(StreamFormat("%d", 123))));
+}
+
 // Helper class that creates a temporary file and exposes a FILE* to it.
 // It will close the file on destruction.
 class TempFile {
@@ -284,6 +332,14 @@ TEST_F(FormatEntryPointTest, FPrintF) {
   EXPECT_EQ(tmp.ReadFile(), "STRING: ABC NUMBER: -000000019");
 }
 
+TEST_F(FormatEntryPointTest, FPrintFWithV) {
+  TempFile tmp;
+  int result =
+      FPrintF(tmp.file(), "STRING: %v NUMBER: %010d", std::string("ABC"), -19);
+  EXPECT_EQ(result, 30);
+  EXPECT_EQ(tmp.ReadFile(), "STRING: ABC NUMBER: -000000019");
+}
+
 TEST_F(FormatEntryPointTest, FPrintFError) {
   errno = 0;
   int result = FPrintF(stdin, "ABC");
@@ -318,6 +374,23 @@ TEST_F(FormatEntryPointTest, PrintF) {
   EXPECT_EQ(result, 30);
   EXPECT_EQ(tmp.ReadFile(), "STRING: ABC NUMBER: -000000019");
 }
+
+TEST_F(FormatEntryPointTest, PrintFWithV) {
+  int stdout_tmp = dup(STDOUT_FILENO);
+
+  TempFile tmp;
+  std::fflush(stdout);
+  dup2(fileno(tmp.file()), STDOUT_FILENO);
+
+  int result = PrintF("STRING: %v NUMBER: %010d", std::string("ABC"), -19);
+
+  std::fflush(stdout);
+  dup2(stdout_tmp, STDOUT_FILENO);
+  close(stdout_tmp);
+
+  EXPECT_EQ(result, 30);
+  EXPECT_EQ(tmp.ReadFile(), "STRING: ABC NUMBER: -000000019");
+}
 #endif  // __GLIBC__
 
 TEST_F(FormatEntryPointTest, SNPrintF) {
@@ -347,9 +420,41 @@ TEST_F(FormatEntryPointTest, SNPrintF) {
   EXPECT_EQ(result, 37);
 }
 
+TEST_F(FormatEntryPointTest, SNPrintFWithV) {
+  char buffer[16];
+  int result =
+      SNPrintF(buffer, sizeof(buffer), "STRING: %v", std::string("ABC"));
+  EXPECT_EQ(result, 11);
+  EXPECT_EQ(std::string(buffer), "STRING: ABC");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 123456);
+  EXPECT_EQ(result, 14);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 123456");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 1234567);
+  EXPECT_EQ(result, 15);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 1234567");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 12345678);
+  EXPECT_EQ(result, 16);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 1234567");
+
+  result = SNPrintF(buffer, sizeof(buffer), "NUMBER: %d", 123456789);
+  EXPECT_EQ(result, 17);
+  EXPECT_EQ(std::string(buffer), "NUMBER: 1234567");
+
+  std::string size = "size";
+
+  result = SNPrintF(nullptr, 0, "Just checking the %v of the output.", size);
+  EXPECT_EQ(result, 37);
+}
+
 TEST(StrFormat, BehavesAsDocumented) {
   std::string s = absl::StrFormat("%s, %d!", "Hello", 123);
   EXPECT_EQ("Hello, 123!", s);
+  std::string hello = "Hello";
+  std::string s2 = absl::StrFormat("%v, %d!", hello, 123);
+  EXPECT_EQ("Hello, 123!", s2);
   // The format of a replacement is
   // '%'[position][flags][width['.'precision]][length_modifier][format]
   EXPECT_EQ(absl::StrFormat("%1$+3.2Lf", 1.1), "+1.10");
@@ -364,9 +469,13 @@ TEST(StrFormat, BehavesAsDocumented) {
   //     "s" - string       Eg: "C" -> "C", std::string("C++") -> "C++"
   //           Formats std::string, char*, string_view, and Cord.
   EXPECT_EQ(StrFormat("%s", "C"), "C");
+  EXPECT_EQ(StrFormat("%v", std::string("C")), "C");
   EXPECT_EQ(StrFormat("%s", std::string("C++")), "C++");
+  EXPECT_EQ(StrFormat("%v", std::string("C++")), "C++");
   EXPECT_EQ(StrFormat("%s", string_view("view")), "view");
+  EXPECT_EQ(StrFormat("%v", string_view("view")), "view");
   EXPECT_EQ(StrFormat("%s", absl::Cord("cord")), "cord");
+  EXPECT_EQ(StrFormat("%v", absl::Cord("cord")), "cord");
   // Integral Conversion
   //     These format integral types: char, int, long, uint64_t, etc.
   EXPECT_EQ(StrFormat("%d", char{10}), "10");
@@ -490,6 +599,15 @@ TEST_F(ParsedFormatTest, SimpleChecked) {
             SummarizeParsedFormat(ParsedFormat<'s', '*', 'd'>("%s %.*d")));
 }
 
+TEST_F(ParsedFormatTest, SimpleCheckedWithV) {
+  EXPECT_EQ("[ABC]{d:1$d}[DEF]",
+            SummarizeParsedFormat(ParsedFormat<'d'>("ABC%dDEF")));
+  EXPECT_EQ("{v:1$v}[FFF]{d:2$d}[ZZZ]{f:3$f}",
+            SummarizeParsedFormat(ParsedFormat<'v', 'd', 'f'>("%vFFF%dZZZ%f")));
+  EXPECT_EQ("{v:1$v}[ ]{.*d:3$.2$*d}",
+            SummarizeParsedFormat(ParsedFormat<'v', '*', 'd'>("%v %.*d")));
+}
+
 TEST_F(ParsedFormatTest, SimpleUncheckedCorrect) {
   auto f = ParsedFormat<'d'>::New("ABC%dDEF");
   ASSERT_TRUE(f);
@@ -520,6 +638,23 @@ TEST_F(ParsedFormatTest, SimpleUncheckedCorrect) {
             SummarizeParsedFormat(*dollar));
 }
 
+TEST_F(ParsedFormatTest, SimpleUncheckedCorrectWithV) {
+  auto f = ParsedFormat<'d'>::New("ABC%dDEF");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]{d:1$d}[DEF]", SummarizeParsedFormat(*f));
+
+  std::string format = "%vFFF%dZZZ%f";
+  auto f2 = ParsedFormat<'v', 'd', 'f'>::New(format);
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{v:1$v}[FFF]{d:2$d}[ZZZ]{f:3$f}", SummarizeParsedFormat(*f2));
+
+  f2 = ParsedFormat<'v', 'd', 'f'>::New("%v %d %f");
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{v:1$v}[ ]{d:2$d}[ ]{f:3$f}", SummarizeParsedFormat(*f2));
+}
+
 TEST_F(ParsedFormatTest, SimpleUncheckedIgnoredArgs) {
   EXPECT_FALSE((ParsedFormat<'d', 's'>::New("ABC")));
   EXPECT_FALSE((ParsedFormat<'d', 's'>::New("%dABC")));
@@ -549,6 +684,15 @@ TEST_F(ParsedFormatTest, SimpleUncheckedIncorrect) {
   EXPECT_FALSE((ParsedFormat<'s', 'd', 'g'>::New(format)));
 }
 
+TEST_F(ParsedFormatTest, SimpleUncheckedIncorrectWithV) {
+  EXPECT_FALSE(ParsedFormat<'d'>::New(""));
+
+  EXPECT_FALSE(ParsedFormat<'d'>::New("ABC%dDEF%d"));
+
+  std::string format = "%vFFF%dZZZ%f";
+  EXPECT_FALSE((ParsedFormat<'v', 'd', 'g'>::New(format)));
+}
+
 #if defined(__cpp_nontype_template_parameter_auto)
 
 template <auto T>
@@ -595,6 +739,23 @@ TEST_F(ParsedFormatTest, ExtendedTyping) {
                          's'>::New("%s%s");
   ASSERT_TRUE(v4);
 }
+
+TEST_F(ParsedFormatTest, ExtendedTypingWithV) {
+  EXPECT_FALSE(ParsedFormat<FormatConversionCharSet::d>::New(""));
+  ASSERT_TRUE(ParsedFormat<absl::FormatConversionCharSet::d>::New("%d"));
+  auto v1 = ParsedFormat<'d', absl::FormatConversionCharSet::v>::New("%d%v");
+  ASSERT_TRUE(v1);
+  auto v2 = ParsedFormat<absl::FormatConversionCharSet::d, 'v'>::New("%d%v");
+  ASSERT_TRUE(v2);
+  auto v3 = ParsedFormat<absl::FormatConversionCharSet::d |
+                             absl::FormatConversionCharSet::v,
+                         'v'>::New("%d%v");
+  ASSERT_TRUE(v3);
+  auto v4 = ParsedFormat<absl::FormatConversionCharSet::d |
+                             absl::FormatConversionCharSet::v,
+                         'v'>::New("%v%v");
+  ASSERT_TRUE(v4);
+}
 #endif
 
 TEST_F(ParsedFormatTest, UncheckedCorrect) {
@@ -638,6 +799,28 @@ TEST_F(ParsedFormatTest, UncheckedCorrect) {
             SummarizeParsedFormat(*dollar));
 }
 
+TEST_F(ParsedFormatTest, UncheckedCorrectWithV) {
+  auto f =
+      ExtendedParsedFormat<absl::FormatConversionCharSet::d>::New("ABC%dDEF");
+  ASSERT_TRUE(f);
+  EXPECT_EQ("[ABC]{d:1$d}[DEF]", SummarizeParsedFormat(*f));
+
+  std::string format = "%vFFF%dZZZ%f";
+  auto f2 = ExtendedParsedFormat<
+      absl::FormatConversionCharSet::v, absl::FormatConversionCharSet::d,
+      absl::FormatConversionCharSet::kFloating>::New(format);
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{v:1$v}[FFF]{d:2$d}[ZZZ]{f:3$f}", SummarizeParsedFormat(*f2));
+
+  f2 = ExtendedParsedFormat<
+      absl::FormatConversionCharSet::v, absl::FormatConversionCharSet::d,
+      absl::FormatConversionCharSet::kFloating>::New("%v %d %f");
+
+  ASSERT_TRUE(f2);
+  EXPECT_EQ("{v:1$v}[ ]{d:2$d}[ ]{f:3$f}", SummarizeParsedFormat(*f2));
+}
+
 TEST_F(ParsedFormatTest, UncheckedIgnoredArgs) {
   EXPECT_FALSE(
       (ExtendedParsedFormat<absl::FormatConversionCharSet::d,
@@ -691,6 +874,19 @@ TEST_F(ParsedFormatTest, UncheckedIncorrect) {
                             absl::FormatConversionCharSet::g>::New(format)));
 }
 
+TEST_F(ParsedFormatTest, UncheckedIncorrectWithV) {
+  EXPECT_FALSE(ExtendedParsedFormat<absl::FormatConversionCharSet::d>::New(""));
+
+  EXPECT_FALSE(ExtendedParsedFormat<absl::FormatConversionCharSet::d>::New(
+      "ABC%dDEF%d"));
+
+  std::string format = "%vFFF%dZZZ%f";
+  EXPECT_FALSE(
+      (ExtendedParsedFormat<absl::FormatConversionCharSet::v,
+                            absl::FormatConversionCharSet::d,
+                            absl::FormatConversionCharSet::g>::New(format)));
+}
+
 TEST_F(ParsedFormatTest, RegressionMixPositional) {
   EXPECT_FALSE(
       (ExtendedParsedFormat<absl::FormatConversionCharSet::d,
@@ -710,11 +906,22 @@ TEST_F(FormatWrapperTest, ConstexprStringFormat) {
   EXPECT_EQ(WrappedFormat("%s there", "hello"), "hello there");
 }
 
+TEST_F(FormatWrapperTest, ConstexprStringFormatWithV) {
+  std::string hello = "hello";
+  EXPECT_EQ(WrappedFormat("%v there", hello), "hello there");
+}
+
 TEST_F(FormatWrapperTest, ParsedFormat) {
   ParsedFormat<'s'> format("%s there");
   EXPECT_EQ(WrappedFormat(format, "hello"), "hello there");
 }
 
+TEST_F(FormatWrapperTest, ParsedFormatWithV) {
+  std::string hello = "hello";
+  ParsedFormat<'v'> format("%v there");
+  EXPECT_EQ(WrappedFormat(format, hello), "hello there");
+}
+
 }  // namespace
 ABSL_NAMESPACE_END
 }  // namespace absl