Use default cpp fmt build script.

vendor/Fmt/test/fuzzing/fuzzer-common.h

@@ -0,0 +1,75 @@
+// Copyright (c) 2019, Paul Dreik
+// For the license information refer to format.h.
+
+#ifndef FUZZER_COMMON_H
+#define FUZZER_COMMON_H
+
+#include <cstdint>      // std::uint8_t
+#include <cstring>      // memcpy
+#include <vector>
+
+#include <fmt/core.h>
+
+// One can format to either a string, or a buffer. The latter is faster, but
+// one may be interested in formatting to a string instead to verify it works
+// as intended. To avoid a combinatoric explosion, select this at compile time
+// instead of dynamically from the fuzz data.
+#define FMT_FUZZ_FORMAT_TO_STRING 0
+
+// If {fmt} is given a buffer that is separately allocated, chances that address
+// sanitizer detects out of bound reads is much higher. However, it slows down
+// the fuzzing.
+#define FMT_FUZZ_SEPARATE_ALLOCATION 1
+
+// The size of the largest possible type in use.
+// To let the the fuzzer mutation be efficient at cross pollinating between
+// different types, use a fixed size format. The same bit pattern, interpreted
+// as another type, is likely interesting.
+constexpr auto fixed_size = 16;
+
+// Casts data to a char pointer.
+template <typename T> inline const char* as_chars(const T* data) {
+  return reinterpret_cast<const char*>(data);
+}
+
+// Casts data to a byte pointer.
+template <typename T> inline const std::uint8_t* as_bytes(const T* data) {
+  return reinterpret_cast<const std::uint8_t*>(data);
+}
+
+// Blits bytes from data to form an (assumed trivially constructible) object
+// of type Item.
+template <class Item> inline Item assign_from_buf(const std::uint8_t* data) {
+  auto item = Item();
+  std::memcpy(&item, data, sizeof(Item));
+  return item;
+}
+
+// Reads a boolean value by looking at the first byte from data.
+template <> inline bool assign_from_buf<bool>(const std::uint8_t* data) {
+  return *data != 0;
+}
+
+struct data_to_string {
+#if FMT_FUZZ_SEPARATE_ALLOCATION
+  std::vector<char> buffer;
+
+  data_to_string(const uint8_t* data, size_t size, bool add_terminator = false)
+      : buffer(size + (add_terminator ? 1 : 0)) {
+    std::memcpy(buffer.data(), data, size);
+  }
+
+  fmt::string_view get() const { return {buffer.data(), buffer.size()}; }
+#else
+  fmt::string_view sv;
+
+  data_to_string(const uint8_t* data, size_t size, bool = false)
+      : str(as_chars(data), size) {}
+
+  fmt::string_view get() const { return sv; }
+#endif
+
+  const char* data() const { return get().data(); }
+};
+
+#endif  // FUZZER_COMMON_H