Re: The Dreaded "Missing Subunits"

[Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>]

Robert A Duff <bobduff@shell01.TheWorld.com> writes:

> Anyway, this all seems rather convoluted.  Why can't the
> compiler/builder automatically determine which compilation units are in
> which files?  Why is a separate tool needed?  And a separate file of
> pragmas Source_File_Name to maintain?

In order for the compiler to determine which compilation units are in
which files, it has to read all the files in the compilation
environment, build the list of file -> unit name mappings, and then
compile them. gnatname + gnatmake does this (caveat; I don't use
gnatname). 

You said this would be "too slow"; which requirement do you really
want? speed or naming convenience?

It's faster if you cache the results of the name scan; gnatname does
this. But as you say, the make system has to be able to determine when
to rerun gnatname, or do it incrementally.

One of the requirements of the GNAT design is the source-based
"library"; there are no data structures required to run the compiler,
other than the source files. Running gnatname automatically starts to
violate this principle.

ObjectAda takes a different approach; you have to manually tell it
what files are in the compilation environment (at least, last time I
used it; one reason I gave it up :). No possibility to automatically
rescan for new files.

> Furthermore, none of this mumbo-jumbo would be necessary at all, if
> only all Ada compilers agreed on the file naming convention. 

Doesn't seem likely, especially now.

> (I must admit, that wasn't easy in the days when operating systems
> had unreasonable limits on file names (like only one dot, or only 8
> characters). Are those bad-old-days over?)

I hope they are over. But we are stuck with their legacy; all of the
GNAT compiler source files are krunched to 8.3 names.

> I also admit that C has it easy in this regard, since it has no
> proper notion of "module" separate from source file.

That is part of the problem.

-- 
-- Stephe