List unused files in Gnat

Question

I have a project in GNAT and I would like to list all the files that are never used. I am thinking about doing it with a python script, but, is it possible to do so easily with GNAT?

Update:

I found about gnatelim, but although in the help it says to have the -P option

usage: gnatelim [options] -main=main_unit_name {filename} [-cargs gcc_switches]

options:
 --version - Display version and exit
 --help    - Display usage and exit

 -Pproject     - Use project file project. Only one such switch can be used.

It seems that it does not work as it asks for a main unit (having the whole project!):

>gnatelim -Prelease.gpr
gnatelim: No main unit specified
try "gnatelim.exe --help" for more information.

I am using GNAT 2015

Answer 1

As a follow-up to Jacob's answer, it seems necessary to pass to gnatelim

• exactly one main unit, taken from those named in the project file
• the project file

For example, in a project file I have several main units listed as

for Main use ("pack-prog.ada", "driver.ada", ...);

(and also for Executable ("pack-prog.ada") use ("prog"); etc.)

Specifying either zero units, as you did, or more than one main unit, I get

$ gnatelim -Pasnip pack-prog.ada driver.ada  
gnatelim: No main unit specified  
try "gnatelim --help" for more information.  

Specifying exactly one unit, I get

$ gnatelim -Pasnip pack-prog.ada
---------------------------------------------------------
--  List of unused entities to be placed in gnat.adc.  --
---------------------------------------------------------
pragma Eliminate (...

The diagnostic message of gnatelim, or via gnatelim, seems not entirely adequate.

Answer 2

The help for gnatelim is rather limited, but I have experimented a bit, and the trick seems to be to pass gnatelim the file name of your main unit:

gnatelim main.adb

If your project is more complicated than a single directory containing all needed source files, you pass gnatelim both a project file and the file name of your main unit:

gnatelim -P black_examples.gpr client.adb

Answer 3

If your project doesn't have any main units, the answer is very simple; nothing is used.

You need to have at least one main unit, to have a reference from which to look at which units aren't used.

In practice there is a much simpler possibility than using gnatelim. Combine the -gnatwe (treat warnings as errors) with -gnatwa (turn on most warnings), and GNAT will tell you which withed units aren't really needed.