D.10.3 Debugging with TeX

You can also catch mistakes when you format a file with TeX.

Usually, you will want to do this after you have run texinfo-format-buffer (or, better, makeinfo-buffer) on the same file, because texinfo-format-buffer sometimes displays error messages that make more sense than TeX. (See Catching Errors with Info Formatting, for more information.)

For example, TeX was run on a Texinfo file, part of which is shown here:

---------- Buffer: texinfo.texi ----------
name of the Texinfo file as an extension.  The
@samp{??} are `wildcards' that cause the shell to
substitute all the raw index files.  (@xref{sorting
indices, for more information about sorting
---------- Buffer: texinfo.texi ----------

(The cross-reference lacks a closing brace.) TeX produced the following output, after which it stopped:

---------- Buffer: *tex-shell* ----------
Runaway argument?
{sorting indices, for more information about sorting
indices.) @ETC.
! Paragraph ended before @xref was complete.
<to be read again>

---------- Buffer: *tex-shell* ----------

In this case, TeX produced an accurate and understandable error message:

Paragraph ended before @xref was complete.

@par’ is an internal TeX command of no relevance to Texinfo. ‘l.27’ means that TeX detected the problem on line 27 of the Texinfo file. The ‘?’ is the prompt TeX uses in this circumstance.

Unfortunately, TeX is not always so helpful, and sometimes you must truly be a Sherlock Holmes to discover what went wrong.

In any case, if you run into a problem like this, you can do one of three things.

  1. You can tell TeX to continue running and ignore just this error by typing RET at the ‘?’ prompt.
  2. You can tell TeX to continue running and to ignore all errors as best it can by typing r RET at the ‘?’ prompt.

    This is often the best thing to do. However, beware: the one error may produce a cascade of additional error messages as its consequences are felt through the rest of the file. To stop TeX when it is producing such an avalanche of error messages, type C-c (or C-c C-c, if you are running a shell inside Emacs).

  3. You can tell TeX to stop this run by typing x RET at the ‘?’ prompt.

If you are running TeX inside Emacs, you need to switch to the shell buffer and line at which TeX offers the ‘?’ prompt.

Sometimes TeX will format a file without producing error messages even though there is a problem. This usually occurs if a command is not ended but TeX is able to continue processing anyhow. For example, if you fail to end an itemized list with the @end itemize command, TeX will write a DVI file that you can print out. The only error message that TeX will give you is the somewhat mysterious comment:

(@end occurred inside a group at level 1)

However, if you print the DVI file, you will find that the text of the file that follows the itemized list is entirely indented as if it were part of the last item in the itemized list. The error message is the way TeX says that it expected to find an @end command somewhere in the file; but that it could not determine where it was needed.

Another source of notoriously hard-to-find errors is a missing @end group command. If you ever are stumped by incomprehensible errors, look for a missing @end group command first.

If the Texinfo file lacks header lines, TeX may stop in the beginning of its run and display output that looks like the following. The ‘*’ indicates that TeX is waiting for input.

This is TeX, Version 3.14159 (Web2c 7.0)
(test.texinfo [1])

In this case, simply type \end RET after the asterisk. Then write the header lines in the Texinfo file and run the TeX command again. (Note the use of the backslash, ‘\’. TeX uses ‘\’ instead of ‘@’; and in this circumstance, you are working directly with TeX, not with Texinfo.)