Reintroduce sprintf_format for ABI compatibility

src/format.cc

@@ -8,6 +8,119 @@
 #include "fmt/format-inl.h"
 
 FMT_BEGIN_NAMESPACE
+namespace internal {
+
+template <typename T>
+int format_float(char* buf, std::size_t size, const char* format, int precision,
+                 T value) {
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+  if (precision > 100000)
+    throw std::runtime_error(
+        "fuzz mode - avoid large allocation inside snprintf");
+#endif
+  // Suppress the warning about nonliteral format string.
+  auto snprintf_ptr = FMT_SNPRINTF;
+  return precision < 0 ? snprintf_ptr(buf, size, format, value)
+                       : snprintf_ptr(buf, size, format, precision, value);
+}
+struct sprintf_specs {
+  int precision;
+  char type;
+  bool alt : 1;
+
+  template <typename Char>
+  constexpr sprintf_specs(basic_format_specs<Char> specs)
+      : precision(specs.precision), type(specs.type), alt(specs.alt) {}
+
+  constexpr bool has_precision() const { return precision >= 0; }
+};
+
+// This is deprecated and is kept only to preserve ABI compatibility.
+template <typename Double>
+char* sprintf_format(Double value, internal::buffer<char>& buf,
+                     sprintf_specs specs) {
+  // Buffer capacity must be non-zero, otherwise MSVC's vsnprintf_s will fail.
+  FMT_ASSERT(buf.capacity() != 0, "empty buffer");
+
+  // Build format string.
+  enum { max_format_size = 10 };  // longest format: %#-*.*Lg
+  char format[max_format_size];
+  char* format_ptr = format;
+  *format_ptr++ = '%';
+  if (specs.alt || !specs.type) *format_ptr++ = '#';
+  if (specs.precision >= 0) {
+    *format_ptr++ = '.';
+    *format_ptr++ = '*';
+  }
+  if (std::is_same<Double, long double>::value) *format_ptr++ = 'L';
+
+  char type = specs.type;
+
+  if (type == '%')
+    type = 'f';
+  else if (type == 0 || type == 'n')
+    type = 'g';
+#if FMT_MSC_VER
+  if (type == 'F') {
+    // MSVC's printf doesn't support 'F'.
+    type = 'f';
+  }
+#endif
+  *format_ptr++ = type;
+  *format_ptr = '\0';
+
+  // Format using snprintf.
+  char* start = nullptr;
+  char* decimal_point_pos = nullptr;
+  for (;;) {
+    std::size_t buffer_size = buf.capacity();
+    start = &buf[0];
+    int result =
+        format_float(start, buffer_size, format, specs.precision, value);
+    if (result >= 0) {
+      unsigned n = internal::to_unsigned(result);
+      if (n < buf.capacity()) {
+        // Find the decimal point.
+        auto p = buf.data(), end = p + n;
+        if (*p == '+' || *p == '-') ++p;
+        if (specs.type != 'a' && specs.type != 'A') {
+          while (p < end && *p >= '0' && *p <= '9') ++p;
+          if (p < end && *p != 'e' && *p != 'E') {
+            decimal_point_pos = p;
+            if (!specs.type) {
+              // Keep only one trailing zero after the decimal point.
+              ++p;
+              if (*p == '0') ++p;
+              while (p != end && *p >= '1' && *p <= '9') ++p;
+              char* where = p;
+              while (p != end && *p == '0') ++p;
+              if (p == end || *p < '0' || *p > '9') {
+                if (p != end) std::memmove(where, p, to_unsigned(end - p));
+                n -= static_cast<unsigned>(p - where);
+              }
+            }
+          }
+        }
+        buf.resize(n);
+        break;  // The buffer is large enough - continue with formatting.
+      }
+      buf.reserve(n + 1);
+    } else {
+      // If result is negative we ask to increase the capacity by at least 1,
+      // but as std::vector, the buffer grows exponentially.
+      buf.reserve(buf.capacity() + 1);
+    }
+  }
+  return decimal_point_pos;
+}
+}  // namespace internal
+
+template FMT_API char* internal::sprintf_format(double, internal::buffer<char>&,
+                                                sprintf_specs);
+template FMT_API char* internal::sprintf_format(long double,
+                                                internal::buffer<char>&,
+                                                sprintf_specs);
+
 template struct FMT_API internal::basic_data<void>;
 
 // Workaround a bug in MSVC2013 that prevents instantiation of format_float.