SysUtils.ShowException() allocates on (possibly corrupt) heap while promising not to do so

Summary

The documentation for 3.2.2 states the following :

The exception message can be at most 255 characters long: It is possible that no memory can be allocated on the heap, so ansistrings are not available, so a shortstring is used to display the message.

And there's also a corresponding comment near the function body:

// use shortstring. On exception, the heap may be corrupt.

However, the function code calls SysUtils.ExceptionErrorMessage(), which uses the heap explicitly:

• it calls Format() which both takes and returns heap-based AnsiString values;

• it stores the result of Format() in its own local AnsiString variable, from which it then copies to the output buffer.

System Information

• Compiler versions: 3.2.2, trunk (f94f4e4e)

Possible fixes

Requires an implementation of Format() that either returns an explicit ShortString or outputs its result to a buffer provided by user. Unfortunately, FormatBuf() is unsuitable, as it is currently just a silly wrapper around Format() itself.

The ExceptionErrorMessage() function should be fixed too, because its requirement for heap makes it practically useless in the exception handling situations it is intended for.