The documentation of AC_LANG_PUSH/POP is not clear enough

[Vladimir Panov]

Hi.

Reading the documentation of  AC_LANG_PUSH and AC_LANG_POP one (e.g. me 
:-) might be lured to use them this way:

AC_DEFUN([CHECK1],
   [
       AC_LANG_PUSH(C)
       ...
       AC_LANG_POP(C)
   ])

AC_DEFUN([CHECK2],
   [
       find2()
       {
           ...
           CHECK1
           ...
           AC_LINK_IFELSE(...)
           ...
       }

       AC_LANG_PUSH(C++)
       find2
       AC_LANG_POP(C++)
   ])

The AC_LINK_IFELSE expansion will be executed with the language set to 
C, because there is actually no stack during configure's execution. The 
workaround is simple - just move AC_LANG_PUSH(C++) at the very beginning 
of CHECK2.

So, I would suggest that the documentation makes it clear that the stack 
is not a runtime one. And maybe give the advice that AC_LANG_PUSH/POP 
are placed immediately at the top/bottom of the macro, thus surrounding 
shell functions (which make the execution non-linear).

Vlado