mjhjmtu

I started to use the nice arara package to automate my compilation process for my thesis.

I know it is better to place the rules using e.g. % arara : pdflatex placed at the beginning of the .tex file to be compiled but I was wondering if it was possible to place this call inside an file called with input....

The reason is the following :

I would like to use arara on multiple files but these do not posess any rules.
However, they share some header.tex file containing macro and style definitions, which is called with input just after the documentclass definition.

So I'd rather modify the common header.tex file instead of all my other files.

I am sorry, arara limits the directive lookup scope to the current document. It would be quite challenging to detect special macros and process them accordingly, like following a file through input, include or similar streams. It is really by design.

That's being said, I've been thinking of adding a new feature in the near future called metadirective. That way, we can change the inner workings of the tool itself at runtime. Sorry if it sounds too vague for now, but your question seems to be one of the cases a metadirective could be used for external file reading. I still do not have the faintest idea of how it would be. :)

However, as alephzero mentioned in the comments, correctly parsing TeX would require a TeX engine in itself to resolve nontrivial scenarios. I want arara to be the emacs of the TeX world, but not quite the TeX engine of the TeX world (yet). :) Let me check how things go in the next weeks, so I can work on a new feature draft.

Regarding your scenario, perhaps the --preamble command line flag could be of interest. To quote my lovely user manual that took me a lifetime to write it: :)

Some TeX documents require the same automation steps, e.g, a set of articles. To this end, so as to avoid repeating the same preamble over and over in this specific scenario, arara has the possibility of setting predefined preambles in a special section of the configuration file identified by a unique key for later use. This command line option prepends the predefined preamble referenced by the name key to the current document and then proceeds to extract directives, as usual. For instance:

twopdftex: |
% arara: pdftex
% arara: pdftex

Source file: doc9.tex:

Hello world.
bye

In this example, we have a preamble named twopdftex and a TeX file named doc9.tex with no directives. Of course, our tool will complain about missing directives, unless we deliberately inject the two directives from the predefined preamble into the current execution:

$ arara -p twopdftex doc9.tex
....
Processing 'doc9.tex' (size: 18 bytes, last modified: 05/29/2018
14:39:21), please wait.
(PDFTeX) PDFTeX engine .................................. SUCCESS
(PDFTeX) PDFTeX engine .................................. SUCCESS
Total: 0.96 seconds

Hope it helps. :)

While arara cannot figure out what files are going to be read you can write a directive that will call arara on a different file. I think I have a workflow somewhat similar to yours where I want all my directives in a file called something like header.tex and I work on body.tex. I list all my directives in header.tex and in body.tex I have a single directive

% arara: mainfile: rootfile: header.tex 

This directive is defined as mainfile.yaml:

identifier: mainfile
name: MAINFILE
commands:
- name: Run Arara on file
 command: >
 @
 return getCommand('arara', '-v', rootfile);
 
arguments:
- identifier: rootfile
 flag: >
 @
 return parameters.rootfile;
 

If you want to automatically deal with directives spread across arbitrary files that may or may not be included, you might be able to hack something together with listfiles to output all the files that are loaded and then have a new directive that calls mainfile on all the sub files, but this sounds difficult and probably not worth it.