Re: access to include path in front end

[Michael Matz <matz@suse.de>]

Hello,

On Tue, 29 Nov 2022, James K. Lowden wrote:

> I don't understand how to access in a front end the arguments to the -I
> option on the command line.  
> 
> Cobol has a feature similar to the C preprecessor, known as the
> Compiler Directing Facility (CDF).  The CDF has a COPY statement that
> resembles an #include directive in C, and shares the property that COPY
> names a file that is normally found in a "copybook" which, for our
> purposes, is a directory of such files.  The name of that directory is
> defined outside the Cobol program.  
> 
> I would like to use the -I option to pass the names of copybook
> directories to the cobol front end.  A bit of exploration yesterday left
> me with the sense that the -I argument, in C at least, is not passed to
> the compiler, but to the preprocessor. Access to -fmax-errors I think
> I've figured out, but -I is a mystery. 
> 
> I'm a little puzzled by the status quo as I understand it.  Unless I
> missed it, it's not discussed in gccint.  ISTM ideally there would be
> some kind of getopt(3) processing, and the whole set of command-line
> options captured in an array of structures accessible to any front
> end.

There is, it's just much more complicated than getopt :)

If you're looking at the C frontends for inspiration, then:

c-family/c.opt defines which options are recognized and several specifics 
about them, e.g. for -I it has:

----
I
C ObjC C++ ObjC++ Joined Separate MissingArgError(missing path after %qs)
-I <dir>        Add <dir> to the end of the main include path.
----

(look at some other examples therein, also in common.opt to get a feel).

Then code in c-family/c-opts.c:c_common_handle_option actually handles the 
option:

    case OPT_I:
      if (strcmp (arg, "-"))
        add_path (xstrdup (arg), INC_BRACKET, 0, true);
      else
      .,.

That function is made a langhook for option processing so that it's 
actually called via c/c-objc-common.h:

  #define LANG_HOOKS_HANDLE_OPTION c_common_handle_option

If you're also using the model of a compiler driver (i.e. the gcc program, 
source in gcc.cc) that actually calls compiler (cc1), assembler and 
linker, then you also need to arrange for that program to pass all -I 
options to the compiler proper.  That is done with the spec language, by 
somewhere having '{I*}' in the specs for invoking the cobol compiler.  
E.g. look in gcc.cc for '@c' (matching the file extension) how that entry 
uses '%(cpp_unique_options)', and how cpp_unique_options is defined for 
the specs language:

  INIT_STATIC_SPEC ("cpp_unique_options",       &cpp_unique_options),

and

static const char *cpp_unique_options =
  "%{!Q:-quiet} %{nostdinc*} %{C} %{CC} %{v} %@{I*&F*} %{P} %I\  

(the specs language used here is documented in a lengthy comment early in 
gcc.cc, "The Specs Language")

The "%@{I*F*}" is the one that makes gcc pass -Iwhatever to cc1 (and 
ensures relative order with -F options is retained and puts all these into 
an @file if one is given on the cmdline, otherwise leaves it on cmdline).  
If you use the compiler driver then using '-v' when invoking it will 
quickly tell you if that options passing worked, as it will show the 
concrete command it exec's for the compiler proper.

Hope this helps.


Ciao,
Michael.