Cygwin: font-lock crashes on XEmacs 21.4.20

[An Isabelle Developer]

Certain complex response from the prover (Isabelle2007) can make font-lock crash when processing the output for display in *response* buffer. The included file "bad.output" has been fetched from the *isabelle* buffer in the critical situation. It can be replayed by starting a fresh Isabelle2007 / Proof General session on Cygwin and issuing the following Isar command:

ML {* Output.std_output (File.read (Path.explode "bad.output")) *}

This will result in tons of messages like this:

(1) (error/warning) Error in process filter: (args-out-of-range *response* 330313 345908)

(2) (error/warning) Error in process filter: (args-out-of-range *response* 314717 330312)

(3) (error/warning) Error in process filter: (args-out-of-range *response* 299121 314716)

(4) (error/warning) Error in process filter: (args-out-of-range *response* 283525 299120)

The problem seems to be specific to Cygwin or the particular XEmacs 21.4.20 installation of that distribution. It works fine on various Linux installations of with XEmacs 21.4.21/22.

[David Aspinall]

Thanks for the report.

Unfortunately I'm not able to test on Cygwin so I cannot investigate this problem and it sounds difficult to debug by email. Have you tried any different Emacs versions (e.g., GNU Emacs)? Please advise if you find a working version.

If unavoidable, you can turn off the font lock for output:

   ProofGeneral -> Advanced -> Customize -> Proof User Options -> Proof Output Fontify Enable

I'm closing this bug for now until more information or an opportunity to test on Windows arrives.