How to pass a variable to a LaTeX code block?

Question

I'd like to set a variable to be expanded in several LaTeX code blocks. For the sake of simplicity, there is only one in this case, foo. :header-args :var is ignored: I presume because LaTeX does not support interactive evaluation? The best I could come up with is verbose. Is there a workaround, for example by using LuaTeX?

foo.org:

#+name: x-val
#+begin_src emacs-lisp :var val=1 :exports none
val
#+end_src

#+RESULTS: x-val
: 1

#+name: foo    
#+begin_src latex :noweb yes :tangle foo.tex
\documentclass{article}
\begin{document}
x = <<x-val()>>
\end{document}
#+end_src

foo.tex

\documentclass{article}
\begin{document}
x = 1
\end{document}

The first and second code blocks are evaluated with C-c C-c and C-u M-x org-babel-tangle, respectively.

UPDATE:

I tried this:

#+PROPERTY: header-args:latex :var val=1

#+name: foo
#+begin_src latex :noweb yes :tangle foo.tex
\documentclass{article}
\begin{document}
x = val
\end{document}
#+end_src

And I get this:

\documentclass{article}
\begin{document}
x = val
\end{document}

init.el (in full) contains config.el (in full) contains:

(org-babel-do-load-languages '(org-babel-load-languages '((latex . t) (python . t))))

Answer 1

This works:

#+name: foo    
#+begin_src latex :noweb yes :tangle foo.tex :var val=1
\documentclass{article}
\begin{document}
x = val
\end{document}
#+end_src

and so does this:

#+PROPERTY: header-args:latex :var val=1

#+name: foo    
#+begin_src latex :noweb yes :tangle foo.tex
\documentclass{article}
\begin{document}
x = val
\end{document}
#+end_src

You have misspelled the property: there should be no colons before or after its name: header-args, not :header-args (that's a frequent source of confusion: see this question) or you have added the PROPERTY and not activated it by pressing C-c C-c on it or closed and reopened the file (another frequent source of confusion).

Answer 2

I noticed an Error upon launching Emacs ("Error (usepackage) org/:init:..."), and I made the following change to the config file (1) :

$ cat ~/.emacs.d/config.el | grep -n5 'org-babel-do' | tail -n5
226-   'org-babel-load-languages
227-   '((emacs-lisp . t) ;; *the change*
228-     (latex . t)
229-     (python . t)))
230-  )

(1) which begs for either of adding, rather than setting, new languages to load, or better yet lazy loading.

And this is satisfactory:

$ touch foo.tex; truncate -s 0 foo.tex
$ emacs +1 foo.org --eval "(org-babel-tangle)"
$ cat foo.tex | grep 'x = '
x = 1

I'm not certain the above change to the configuration is responsible for the error and that in turn is responsible for the seeming satisfactory resolution of the stated problem, so I'll wait for more evidence before accepting this answer.