Make numeric alignment optional

doc/syntax.rst

@@ -101,11 +101,6 @@ The meaning of the various alignment options is as follows:
 | ``'>'`` | Forces the field to be right-aligned within the          |
 |         | available space (this is the default for numbers).       |
 +---------+----------------------------------------------------------+
-| ``'='`` | Forces the padding to be placed after the sign (if any)  |
-|         | but before the digits.  This is used for printing fields |
-|         | in the form '+000000120'. This alignment option is only  |
-|         | valid for numeric types.                                 |
-+---------+----------------------------------------------------------+
 | ``'^'`` | Forces the field to be centered within the available     |
 |         | space.                                                   |
 +---------+----------------------------------------------------------+
@@ -154,9 +149,11 @@ conversions, trailing zeros are not removed from the result.
 *width* is a decimal integer defining the minimum field width.  If not
 specified, then the field width will be determined by the content.
 
-Preceding the *width* field by a zero (``'0'``) character enables
-sign-aware zero-padding for numeric types.  This is equivalent to a *fill*
-character of ``'0'`` with an *alignment* type of ``'='``.
+Preceding the *width* field by a zero (``'0'``) character enables sign-aware
+zero-padding for numeric types. It forces the padding to be placed after the
+sign or base (if any) but before the digits. This is used for printing fields in
+the form '+000000120'. This option is only valid for numeric types and it has no
+effect on formatting of infinity and NaN.
 
 The *precision* is a decimal number indicating how many digits should be
 displayed after the decimal point for a floating-point value formatted with

include/fmt/format.h

@@ -185,6 +185,10 @@ inline uint32_t clzll(uint64_t x) {
 FMT_END_NAMESPACE
 #endif
 
+#ifndef FMT_NUMERIC_ALIGN
+# define FMT_NUMERIC_ALIGN 1
+#endif
+
 FMT_BEGIN_NAMESPACE
 namespace internal {
 
@@ -2300,9 +2304,11 @@ FMT_CONSTEXPR const Char* parse_align(const Char* begin, const Char* end,
     case '>':
       align = align::right;
       break;
+#if FMT_NUMERIC_ALIGN
     case '=':
       align = align::numeric;
       break;
+#endif
     case '^':
       align = align::center;
       break;

test/format-test.cc

@@ -697,12 +697,6 @@ TEST(FormatToTest, WideString) {
   EXPECT_STREQ(buf.data(), L"42");
 }
 
-TEST(FormatToTest, FormatToNonbackInsertIteratorWithSignAndNumericAlignment) {
-  char buffer[16] = {};
-  fmt::format_to(fmt::internal::make_checked(buffer, 16), "{: =+}", 42.0);
-  EXPECT_STREQ("+42.0", buffer);
-}
-
 TEST(FormatToTest, FormatToMemoryBuffer) {
   fmt::basic_memory_buffer<char, 100> buffer;
   fmt::format_to(buffer, "{}", "foo");
@@ -856,6 +850,7 @@ TEST(FormatterTest, RightAlign) {
   EXPECT_EQ("  0xface", format("{0:>8}", reinterpret_cast<void*>(0xface)));
 }
 
+#if FMT_NUMERIC_ALIGN
 TEST(FormatterTest, NumericAlign) {
   EXPECT_EQ("  42", format("{0:=4}", 42));
   EXPECT_EQ("+ 42", format("{0:=+4}", 42));
@@ -882,6 +877,13 @@ TEST(FormatterTest, NumericAlign) {
   EXPECT_EQ(" 1.0", fmt::format("{:= }", 1.0));
 }
 
+TEST(FormatToTest, FormatToNonbackInsertIteratorWithSignAndNumericAlignment) {
+  char buffer[16] = {};
+  fmt::format_to(fmt::internal::make_checked(buffer, 16), "{: =+}", 42.0);
+  EXPECT_STREQ("+42.0", buffer);
+}
+#endif
+
 TEST(FormatterTest, CenterAlign) {
   EXPECT_EQ(" 42  ", format("{0:^5}", 42));
   EXPECT_EQ(" 42  ", format("{0:^5o}", 042));
@@ -2055,8 +2057,10 @@ TEST(FormatTest, DynamicFormatter) {
                    "cannot switch from manual to automatic argument indexing");
   EXPECT_THROW_MSG(format("{:{0}}", num), format_error,
                    "cannot switch from automatic to manual argument indexing");
+#if FMT_NUMERIC_ALIGN
   EXPECT_THROW_MSG(format("{:=}", str), format_error,
                    "format specifier requires numeric argument");
+#endif
   EXPECT_THROW_MSG(format("{:+}", str), format_error,
                    "format specifier requires numeric argument");
   EXPECT_THROW_MSG(format("{:-}", str), format_error,
@@ -2439,13 +2443,15 @@ TEST(FormatTest, FormatStringErrors) {
   EXPECT_ERROR("{0:s", "unknown format specifier", Date);
 #  if FMT_MSC_VER >= 1916
   // This causes an internal compiler error in MSVC2017.
-  EXPECT_ERROR("{0:=5", "unknown format specifier", int);
   EXPECT_ERROR("{:{<}", "invalid fill character '{'", int);
   EXPECT_ERROR("{:10000000000}", "number is too big", int);
   EXPECT_ERROR("{:.10000000000}", "number is too big", int);
   EXPECT_ERROR_NOARGS("{:x}", "argument index out of range");
+#if FMT_NUMERIC_ALIGN
+  EXPECT_ERROR("{0:=5", "unknown format specifier", int);
   EXPECT_ERROR("{:=}", "format specifier requires numeric argument",
                const char*);
+#endif
   EXPECT_ERROR("{:+}", "format specifier requires numeric argument",
                const char*);
   EXPECT_ERROR("{:-}", "format specifier requires numeric argument",

test/ostream-test.cc

@@ -95,8 +95,10 @@ TEST(OStreamTest, Format) {
 TEST(OStreamTest, FormatSpecs) {
   EXPECT_EQ("def  ", format("{0:<5}", TestString("def")));
   EXPECT_EQ("  def", format("{0:>5}", TestString("def")));
+#if FMT_NUMERIC_ALIGN
   EXPECT_THROW_MSG(format("{0:=5}", TestString("def")), format_error,
                    "format specifier requires numeric argument");
+#endif
   EXPECT_EQ(" def ", format("{0:^5}", TestString("def")));
   EXPECT_EQ("def**", format("{0:*<5}", TestString("def")));
   EXPECT_THROW_MSG(format("{0:+}", TestString()), format_error,

test/std-format-test.cc

@@ -30,18 +30,14 @@ TEST(StdFormatTest, Alignment) {
   // Error: '=' with charT and no integer presentation type
   EXPECT_THROW(string s5 = format("{:=6}", 'x'), std::format_error);
   string s6 = format("{:6d}", c);       // s6 == "   120"
-  string s7 = format("{:=+06d}", c);    // s7 == "+00120"
-  string s8 = format("{:0=#6x}", 0xa);  // s8 == "0x000a"
-  string s9 = format("{:6}", true);     // s9 == "true  "
+  string s7 = format("{:6}", true);     // s9 == "true  "
   EXPECT_EQ(s0, "    42");
   EXPECT_EQ(s1, "x     ");
   EXPECT_EQ(s2, "x*****");
   EXPECT_EQ(s3, "*****x");
   EXPECT_EQ(s4, "**x***");
   EXPECT_EQ(s6, "   120");
-  EXPECT_EQ(s7, "+00120");
-  EXPECT_EQ(s8, "0x000a");
-  EXPECT_EQ(s9, "true  ");
+  EXPECT_EQ(s7, "true  ");
 }
 
 TEST(StdFormatTest, Float) {