[Emacs-ada-mode] Default build command is stuck to the first "Compile file" command line

[Alexy Khrabrov]

I'm using gnatmake, etc., installed in /usr/local/ada/bin, and the  
latter directory is not on my PATH -- so that GNAT's gcc is not  
confused with the system-wide one.

I'd like ada-mode to find it properly.  At first I thought I'll just  
create a system-wide gnat.adp file, with one line:

cross_prefix=/usr/local/ada/bin/

and then, in my ~/.emacs, will set that as my default project.  That  
works in the same way as another approach:

(setq gnat-bin-dir "/usr/local/ada/bin")
(setenv "PATH" (concat gnat-bin-dir ":" (getenv "PATH")))

By the way, the following, which I tried before setenv "PATH", didn't  
work:

(add-to-list 'exec-path gnat-bin-dir)

-- apparently the commands form ada-mode invoke my shell, zsh,  
directly, and its PATH is searched, without any exec-path usage at  
all.  Thus an elisp question: how do we ensure, instead of just  
prepending, that we prepend gnat-bin-dir to PATH only once, when it's  
not there already?  Is there a standard way to do it with elisp,  
similar to the add-to-list function for adding an element to a list  
(such as exec-path) just once?

In both cases, I get the same undesirable behavior -- the build  
command gets stuck on whatever form it got on the first try.  If I  
first try to build with C-c C-c, Emacs asks me, "enter command to  
compile:" -- I C-g out of it and go to the Ada menu, choose "Compile  
file", it compiles the current buffer with gnatmake -o  
<current_buffer_filename's basename> ... command line, fails if it's  
a package or otherwise not the main procedure, and then every attempt  
to run C-c C-c invokes the same command line with that very file's -o  
basename, which fails again.

How does Ada Mode knows which is the main procedure, and how are we  
supposed to start the compile/build sequence to end up with the  
correct C-c C-c?

I unpacked the latest ada-mode, 2007-11-14, and made it first on my  
load-path.  Do I need any of the other three .el files in addition to  
that?  They are

ada-mode-patches.el
ada-mode-keys.el
gnat-fix-error.el

I'm using GNU Emacs 22.0.90.1 (i386-apple-darwin8.8.1, Carbon Version  
1.6.0)
  of 2006-10-28 on petit.local.

BTW, a minor suggestion: when I don't specify the default Ada Mode  
project and try editing it with C-c u, and then enter /usr/local/ada/ 
bin/ into cross_prefix field and hit [Save], I get an error: Wrong  
type argument: stringp, nil.  Also learned to specify the  
cross_prefix with a trailing slash, as it's being concatenated to the  
commands without an interceding slash, such as in ${cross_prefix} 
gnatmake.  Perhaps it's safer to code it up as ${cross_prefix}/ 
gnatmake in case folks forget to add the trailing slash when editing  
the project files.

Cheers,
Alexy