What to do if the `pdflatex` command failed to run because of change of the Tex-master variable.

Problem

After I duplicated one of my LaTeX project folders and changed the name of the main file, the compile command will not find the new main file.

It worked fine if I compiled within the main file. However, when I changed the bottom matters of the sub-source .tex files, the AUCTeX failed to recognize the new main file name.

The project has the following files (simplified for illustration purpose):

• new_main.tex (was “old_main.tex”)
• 1_intro.tex
• 2_method.tex
• 3_evaluation.tex
• 4_conclusion.tex

In each of the sub-files, I have the variables section, identifying the main file to use.

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%%% Local Variables: 
%%% mode: latex
%%% TeX-master: "new_main"
%%% End: 

(It was TeX-master: "old_main".) The purpose of this part is that you can initiate the compile command from the sub-source files, without the need to switch back to the main file.

The error message was like:

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Running `LaTeX' on `old_main' with ``pdflatex  -file-line-error  --synctex=1 -interaction=nonstopmode old_main.tex''
This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2018) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
! I can't find file `old_main.tex'.
<*> old_main.tex

(Press Enter to retry, or Control-D to exit)
Please type another input file name
! Emergency stop.
<*> old_main.tex

!  ==> Fatal error occurred, no output PDF file produced!
Transcript written on texput.log.

TeX Output exited abnormally with code 1 at Sun Dec  6 15:58:55

Diagnose

Basically, I changed the name of the main file to use, but the AUCTeX failed to load the new value and kept trying the old_main.

Solution

Go to the sub-source .tex files, run revert-buffer (M-x or in Spacemacs SPC SPC). Done!