Fix 2dffa7d: fmt::format_to copies the iterator, so some text does not remain during formatting (#10940)

src/strings.cpp

@@ -285,7 +285,7 @@ char *GetString(char *buffr, StringID string, const char *last)
 {
 	_global_string_params.ClearTypeInformation();
 	_global_string_params.offset = 0;
-	StringBuilder builder(buffr, last);
+	StringBuilder builder(&buffr, last);
 	GetStringWithArgs(builder, string, &_global_string_params);
 	return builder.GetEnd();
 }
@@ -313,7 +313,8 @@ std::string GetString(StringID string)
 std::string GetStringWithArgs(StringID string, StringParameters *args)
 {
 	char buffer[DRAW_STRING_BUFFER];
-	StringBuilder builder(buffer, lastof(buffer));
+	char *state = buffer;
+	StringBuilder builder(&state, lastof(buffer));
 	GetStringWithArgs(builder, string, args);
 	return std::string(buffer, builder.GetEnd());
 }
@@ -845,11 +846,10 @@ static void FormatString(StringBuilder &builder, const char *str_arg, StringPara
 		 * space allocated for type information and thus wants type checks on
 		 * the parameters. So, we need to gather the type information via the
 		 * dry run first, before we can continue formatting the string.
-		 *
-		 * Create a copy of the state of the builder for the dry run, so we do
-		 * not have to reset it after the dry run has completed.
 		 */
-		StringBuilder dry_run_builder = builder;
+		char buffer[DRAW_STRING_BUFFER];
+		char *state = buffer;
+		StringBuilder dry_run_builder(&state, lastof(buffer));
 		if (UsingNewGRFTextStack()) {
 			/* Values from the NewGRF text stack are only copied to the normal
 			 * argv array at the time they are encountered. That means that if
@@ -1018,9 +1018,10 @@ static void FormatString(StringBuilder &builder, const char *str_arg, StringPara
 					 * enough space for the gender index token, one character
 					 * for the actual gender and one character for '\0'. */
 					char buf[MAX_CHAR_LENGTH + 1 + 1];
+					char *state = buf;
 					bool old_sgd = _scan_for_gender_data;
 					_scan_for_gender_data = true;
-					StringBuilder tmp_builder(buf, lastof(buf));
+					StringBuilder tmp_builder(&state, lastof(buf));
 					StringParameters tmp_params(args->GetPointerToOffset(offset), args->num_param - offset, nullptr);
 					FormatString(tmp_builder, input, &tmp_params);
 					_scan_for_gender_data = old_sgd;

src/strings_internal.h

@@ -20,7 +20,7 @@
  * extra functions to ease the migration from char buffers to std::string.
  */
 class StringBuilder {
-	char *current; ///< The current location to add strings
+	char **current; ///< The current location to add strings
 	const char *last; ///< The last element of the buffer.
 
 public:
@@ -36,7 +36,7 @@ public:
 	 * @param start The start location to write to.
 	 * @param last  The last location to write to.
 	 */
-	StringBuilder(char *start, const char *last) : current(start), last(last) {}
+	StringBuilder(char **start, const char *last) : current(start), last(last) {}
 
 	/* Required operators for this to be an output_iterator; mimics std::back_insert_iterator, which has no-ops. */
 	StringBuilder &operator++() { return *this; }
@@ -62,7 +62,7 @@ public:
 	 */
 	StringBuilder &operator+=(const char value)
 	{
-		if (this->current != this->last) *this->current++ = value;
+		if (*this->current != this->last) *(*this->current)++ = value;
 		return *this;
 	}
 
@@ -73,7 +73,7 @@ public:
 	 */
 	StringBuilder &operator+=(const char *str)
 	{
-		this->current = strecpy(this->current, str, this->last);
+		*this->current = strecpy(*this->current, str, this->last);
 		return *this;
 	}
 
@@ -96,7 +96,7 @@ public:
 	{
 		if (this->Remaining() < Utf8CharLen(c)) return false;
 
-		this->current += ::Utf8Encode(this->current, c);
+		(*this->current) += ::Utf8Encode(*this->current, c);
 		return true;
 	}
 
@@ -108,8 +108,8 @@ public:
 	 */
 	char *GetEnd()
 	{
-		*this->current = '\0';
-		return this->current;
+		**this->current = '\0';
+		return *this->current;
 	}
 
 	/**
@@ -118,7 +118,7 @@ public:
 	 */
 	ptrdiff_t Remaining()
 	{
-		return (ptrdiff_t)(this->last - this->current);
+		return (ptrdiff_t)(this->last - *this->current);
 	}
 
 	/**
@@ -128,7 +128,7 @@ public:
 	 */
 	void AddViaStreCallback(std::function<char*(char*, const char*)> function)
 	{
-		this->current = function(this->current, this->last);
+		*this->current = function(*this->current, this->last);
 	}
 };
 

src/townname.cpp

@@ -67,7 +67,7 @@ static void GetTownName(StringBuilder &builder, const TownNameParams *par, uint3
  */
 char *GetTownName(char *buff, const TownNameParams *par, uint32 townnameparts, const char *last)
 {
-	StringBuilder builder(buff, last);
+	StringBuilder builder(&buff, last);
 	GetTownName(builder, par, townnameparts);
 	return builder.GetEnd();
 }
@@ -92,7 +92,7 @@ void GetTownName(StringBuilder &builder, const Town *t)
  */
 char *GetTownName(char *buff, const Town *t, const char *last)
 {
-	StringBuilder builder(buff, last);
+	StringBuilder builder(&buff, last);
 	GetTownName(builder, t);
 	return builder.GetEnd();
 }