Disallow formatting of multibyte strings into a wide buffer (#606)

include/fmt/format.h

@@ -1112,7 +1112,7 @@ enum type {
   INT, UINT, LONG_LONG, ULONG_LONG, BOOL, CHAR, LAST_INTEGER_TYPE = CHAR,
   // followed by floating-point types.
   DOUBLE, LONG_DOUBLE, LAST_NUMERIC_TYPE = LONG_DOUBLE,
-  CSTRING, STRING, TSTRING, POINTER, CUSTOM
+  CSTRING, STRING, POINTER, CUSTOM
 };
 
 constexpr bool is_integral(type t) {
@@ -1189,10 +1189,10 @@ template <> constexpr type get_type<unsigned char *>() { return CSTRING; }
 template <> constexpr type get_type<const unsigned char *>() { return CSTRING; }
 template <> constexpr type get_type<std::string>() { return STRING; }
 template <> constexpr type get_type<string_view>() { return STRING; }
-template <> constexpr type get_type<wchar_t *>() { return TSTRING; }
-template <> constexpr type get_type<const wchar_t *>() { return TSTRING; }
-template <> constexpr type get_type<std::wstring>() { return TSTRING; }
-template <> constexpr type get_type<wstring_view>() { return TSTRING; }
+template <> constexpr type get_type<wchar_t *>() { return CSTRING; }
+template <> constexpr type get_type<const wchar_t *>() { return CSTRING; }
+template <> constexpr type get_type<std::wstring>() { return STRING; }
+template <> constexpr type get_type<wstring_view>() { return STRING; }
 template <> constexpr type get_type<void *>() { return POINTER; }
 template <> constexpr type get_type<const void *>() { return POINTER; }
 template <> constexpr type get_type<std::nullptr_t>() { return POINTER; }
@@ -1225,10 +1225,9 @@ class value {
     double double_value;
     long double long_double_value;
     const void *pointer;
-    string_value<char> string;
+    string_value<char_type> string;
     string_value<signed char> sstring;
     string_value<unsigned char> ustring;
-    string_value<char_type> tstring;
     custom_value<char_type> custom;
   };
 
@@ -1271,18 +1270,16 @@ class value {
   }
 #endif
 
-  value(char *s) { set<CSTRING>(string.value, s); }
-  value(const char *s) { set<CSTRING>(string.value, s); }
-  value(signed char *s) { set<CSTRING>(sstring.value, s); }
-  value(const signed char *s) { set<CSTRING>(sstring.value, s); }
-  value(unsigned char *s) { set<CSTRING>(ustring.value, s); }
-  value(const unsigned char *s) { set<CSTRING>(ustring.value, s); }
-  value(string_view s) { set_string(s); }
-  value(const std::string &s) { set_string(s); }
-  value(wstring_view s) { set_wstring(s); }
-  value(const std::wstring &s) { set_wstring(s); }
-  value(wchar_t *s) { set_wstring(wstring_view(s)); }
-  value(const wchar_t *s) { set_wstring(wstring_view(s)); }
+  // Formatting of wide strings into a narrow buffer and multibyte strings
+  // into a wide buffer is disallowed (https://github.com/fmtlib/fmt/pull/606).
+  value(char_type *s) { set<CSTRING>(string.value, s); }
+  value(const char_type *s) { set<CSTRING>(string.value, s); }
+  value(signed char *s) { set_cstring(sstring.value, s); }
+  value(const signed char *s) { set_cstring(sstring.value, s); }
+  value(unsigned char *s) { set_cstring(ustring.value, s); }
+  value(const unsigned char *s) { set_cstring(ustring.value, s); }
+  value(basic_string_view<char_type> s) { set_string(s); }
+  value(const std::basic_string<char_type> &s) { set_string(s); }
 
   // Formatting of arbitrary pointers is disallowed. If you want to output a
   // pointer cast it to "void *" or "const void *". In particular, this forbids
@@ -1338,12 +1335,11 @@ class value {
     string.size = value.size();
   }
 
-  template <typename T>
-  void set_wstring(const T &value) {
-    require_wchar<char_type>();
-    static_assert(get_type<T>() == TSTRING, "invalid type");
-    tstring.value = value.data();
-    tstring.size = value.size();
+  template <typename T, typename U>
+  constexpr void set_cstring(T &field, const U *str) {
+    static_assert(std::is_same<char, char_type>::value,
+                  "incompatible string types");
+    set<CSTRING>(field, str);
   }
 
   // Formats an argument of a custom type, such as a user-defined class.
@@ -1439,10 +1435,8 @@ constexpr typename std::result_of<Visitor(int)>::type
   case internal::CSTRING:
     return vis(arg.value_.string.value);
   case internal::STRING:
-    return vis(string_view(arg.value_.string.value, arg.value_.string.size));
-  case internal::TSTRING:
     return vis(basic_string_view<Char>(
-                 arg.value_.tstring.value, arg.value_.tstring.size));
+                 arg.value_.string.value, arg.value_.string.size));
   case internal::POINTER:
     return vis(arg.value_.pointer);
   case internal::CUSTOM:

test/util-test.cc

@@ -563,13 +563,9 @@ TEST(UtilTest, StringArg) {
   char *str = str_data;
   const char *cstr = str;
   CHECK_ARG_(char, cstr, str);
-  CHECK_ARG_(wchar_t, cstr, str);
-  CHECK_ARG(cstr);
 
   string_view sref(str);
   CHECK_ARG_(char, sref, std::string(str));
-  CHECK_ARG_(wchar_t, sref, std::string(str));
-  CHECK_ARG(sref);
 }
 
 TEST(UtilTest, WStringArg) {