With the help of When is the aux file read and written? and Barbara Beetons kind assistance I was able to determine what goes wrong and how to prevent it.
This is the problem:
Normally I then don't work with the TeX engine on the console, but simply correct my error and restart.
This is what I should have done on the console:
- Type
?+Return to get an idea of what can be done.
- Simply hit
Return repeatedly until Tex is finished.
- Type
X+Return to finish the run immediately.
- Type
E+Return to have the cursor jump to the point where the error occurred.
What happens is, that TeX buffers the \write commands to the .aux file in two stages. First stage, it waits until a page is shipped out to get the page numbers right. Second stage, it waits until it sees fit to issue a write() system call, to reduce the number of (potentially slow) system calls. This second buffer seemingly does not care, if the chunks it writes to file are self-contained legal TeX since it will complete the file before the TeX run is finished anyway.
In the environment of TeXShop however it is tempting to let TeX hang unfinished after an error. Thus the second output puffer is not flushed and the .aux file possibly left unfinished and in an illegal state.
My personal conclusion from this: Always let TeX finish.
The assumption that TeX will have a chance to finish it's run after it stopped for an error was very reasonable before windowed environments, where it became easy and normal to leave processes hanging in the background.
Things that could be done on software side to facilitate this user behavior:
- Change Tex's second buffer behavior to issue a
write() system call in case of an error or to break only into TeX-legal chunks.
- Adjust the environment (TexShop) to either clean the .aux file after a process abortion or provide default input to always correctly finish the process.
Things that the user can do, other than always letting TeX finish:
- Use
\include{...}. That way the .aux files of the sections before are closed an finished by the time the error occurs. Chances are the .aux file of your current section isn't large enough yet and no TeX-illegal parts were written.
- Hack something involving
\immediate\closeout\@mainaux followed by an \openout\@mainaux and a copy of the contents so they don't get overwritten. This will effectively flush the output buffer. Does not seem worth the effort though.
Best Answer
The writing of the
.auxfiles in LaTeX is controlled by switch\if@filesw(wshort for writable). The command\nofilessets the switch to false to prevent the rewriting of the auxiliary files.The main
.auxfile is opened for writing in\begin{document}. If the LaTeX job does not reach this point, for example, because of an error or on purpose, the auxiliary files are also not written.