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12.2 The GNAT Driver and Project Files

A number of GNAT tools, other than gnatmake can benefit from project files: (gnatbind, gnatclean, gnatfind, gnatlink, gnatls, and gnatxref). However, none of these tools can be invoked directly with a project file switch (-P). They must be invoked through the gnat driver.

The gnat driver is a wrapper that accepts a number of commands and calls the corresponding tool. It was designed initially for VMS platforms (to convert VMS qualifiers to Unix-style switches), but it is now available on all GNAT platforms.

On non-VMS platforms, the gnat driver accepts the following commands (case insensitive):

(note that the compiler is invoked using the command gnatmake -f -u -c).

On non-VMS platforms, between gnat and the command, two special switches may be used:

The command may be followed by switches and arguments for the invoked tool.

       gnat bind -C main.ali
       gnat ls -a main
       gnat chop foo.txt

Switches may also be put in text files, one switch per line, and the text files may be specified with their path name preceded by '@'.

        gnat bind @args.txt main.ali

In addition, for commands BIND, COMP or COMPILE, FIND, LS or LIST, LINK, and XREF, the project file related switches (-P, -X and -vPx) may be used in addition to the switches of the invoking tool.

For each of the following commands, there is optionally a corresponding package in the main project.

Package Gnatls has a unique attribute Switches, a simple variable with a string list value. It contains switches for the invocation of gnatls.

     project Proj1 is
        package gnatls is
           for Switches
               use ("-a",
        end gnatls;
     end Proj1;

All other packages have two attribute Switches and Default_Switches.

Switches is an indexed attribute, indexed by the source file name, that has a string list value: the switches to be used when the tool corresponding to the package is invoked for the specific source file.

Default_Switches is an attribute, indexed by the programming language that has a string list value. Default_Switches ("Ada") contains the switches for the invocation of the tool corresponding to the package, except if a specific Switches attribute is specified for the source file.

     project Proj is
        for Source_Dirs use ("**");
        package gnatls is
           for Switches use
        end gnatls;
        package Compiler is
           for Default_Switches ("Ada")
               use ("-gnatv",
        end Binder;
        package Binder is
           for Default_Switches ("Ada")
               use ("-C",
        end Binder;
        package Linker is
           for Default_Switches ("Ada")
               use ("-C");
           for Switches ("main.adb")
               use ("-C",
        end Linker;
        package Finder is
           for Default_Switches ("Ada")
                use ("-a",
        end Finder;
        package Cross_Reference is
           for Default_Switches ("Ada")
               use ("-a",
        end Cross_Reference;
     end Proj;

With the above project file, commands such as

        gnat comp -Pproj main
        gnat ls -Pproj main
        gnat xref -Pproj main
        gnat bind -Pproj main.ali
        gnat link -Pproj main.ali

will set up the environment properly and invoke the tool with the switches found in the package corresponding to the tool: Default_Switches ("Ada") for all tools, except Switches ("main.adb") for gnatlink.