4.1 Bug criteria

If you are not sure whether you have found a bug, here are some guidelines:

• If a program gets a fatal signal, for any input whatsoever, that is a bug. Reliable programs never crash.

• If a program produces an invalid font, for any input whatsoever, that is a bug--unless the program reported a fatal error that forced it to quit prematurely. For example, if Metafont gives errors reading the output of bzrto -mf, that is a bug. You can run the TeX utility programs GFtype and TFtoPL to check the validity of a GF or TFM file.

• If a program gives an error message for valid input, that is a bug. Similarly, if a program gives a fatal error when it could continue processing, that is a bug. It is sometimes hard to tell if these conditions obtain; you must use your best judgement.

• If a program does not give an error message for invalid input, that is a bug.