What's the exact time that buffer/file/directory local variables is evaluated in Emacs?

What's the exact time that buffer/file/directory local variables is evaluated in Emacs?

[Hongxu Chen]

Hi guys,

I have often been confused with the time when some local variables are
evaluated in Emacs, especially when I am customizing some settings for
C/C++ mode.

For instance, I added (flymake-mode-on) to `c-mode-hook', however the
specified flymake tool `clang' is dependent on the dir-local variable
`ac-clang-flags'. So whenever I open a c file which requires some
additional flags(such as includes, definition of macros, etc) Flymake
would emit false error/warning messages since it still uses the old
value of `ac-clang-flags'; and only after some changes have been made I
can occasionally see the update of the value. Is there any way to make
it work just right?

Presently I guess the command `normal-mode' may have some effects on the
local variables, but I just cannot figure out the exact time when these
variables are set.

-- 
Thanks,
Hongxu Chen