LaTeX mode: How to select "pdflatex" instead of "latex" for a file automatically?

Question

I have a LaTeX file using lots of PDF figures (mostly because converting figures to EPS is a waste of disk space), so it requires to use pdflatex.

I added these lines to the end of my main file:

%% Local Variables:
%% latex-run-command: pdflatex
%% End:

Whenever when I open the file, Emacs asks me whether to evaluate these settings, and I confirm. However, C-c C-f still runs latex \\nonstopmode\\input input.tex.

Why doesn't it work? (this is the question I should point out clearly)

Also in Customize the setting of latex-run-command still is Standard.

After a significant waste of time, I wrote a Makefile that builds my document (keeping the PDF open in evince). So I use compile to build the file now.

Details:

When I run C-c C-f, the output starts like this:

latex \\nonstopmode\\input Farbe.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/TeX Live for SUSE Linux) (preloaded format=latex)

When I run pdflatex manually, the output starts like this:

pdflatex Farbe
This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/TeX Live for SUSE Linux) (preloaded format=pdflatex)

So the preloaded format is different, causing errors like

! LaTeX Error: Cannot determine size of graphic in RGB-Cube-3D.pdf (no Bounding
Box).

Also, using latex-run-command: "pdflatex" makes no difference: pdflatex is not being used.

More details:

When I load the file (having changed the settings to the following)

%% Local Variables:
%% latex-run-command: "pdflatex"
%% End:

and then do C-h v latex-run-command, I get:

latex-run-command’s value is "pdflatex"
Original value was "latex"
Local in buffer Farbe.tex; global value is "latex"

  This variable’s value is file-local.
  This variable may be risky if used as a file-local variable.

Documentation:
Command used to run LaTeX subjob.
LaTeX Mode sets ‘tex-command’ to this string.
See the documentation of that variable.

But still, the command run is not pdflatex, but latex!

More info (2019-11-28)

My Emacs is 25.3.1, and in loaddefs.el I have:

(defvar latex-run-command (purecopy "latex") "\
Command used to run LaTeX subjob.
LaTeX Mode sets `tex-command' to this string.
See the documentation of that variable.")

And tex-mode.el contains:

(setq-local tex-command latex-run-command)

Even when I tried this, it did nor work:

%% Local Variables:
%% latex--command: "pdflatex"
%% eval: (add-hook 'latex-mode-hook (lambda () \
%%  (setq latex-run-command "pdflatex")))
%% End:

I also had tried variants setq-local, tex-command instead of latex-run-command, but it all did not work.

Neither does it work after having used set-variable interactively to set latex-run-command, nor does it work after I had set the variable in "Customize Option: Latex Run Command".

Answer 1

One problem is the syntax: the value is a string so you need to say so by surrounding it with double quotes. However I could not get this to work with the latex-run-command variable. However tex-command seems to work (for some value of "work"):

%% Local Variables:
%% tex-command: "pdflatex"
%% End:

EDIT: The problem with latex-run-command may be a sequencing problem: when the file is opened, does the mode function get run and then local vars are set? or the other way round? If the mode function is run first, that would explain why the latex-run-comand setting is ineffective: the mode function does

(setq-local tex-command latex-run-command)

so it is probably setting it to the old value, before the local variable setting takes effect. You can try customizing latex-run-command and restarting emacs: I suspect that that would work.

Answer 2

The documentation does not match the implementation, or the implementation is broken: The variable latex-run-command was changed from "latex" to "pdflatex", but command tex-file (found in latex-mode-map) still uses latex \\nonstopmode\\input.