Re: Can we deprecate $subdir?

[Jacob Bachmeyer]

Ben Elliston wrote:
> On Sat, Nov 24, 2018 at 07:43:41PM -0600, Jacob Bachmeyer wrote:
>   
> > As part of the ongoing effort to improve Automake integration and
> > mindful of the eventual goal to run test scripts in slave
> > interpreters, I have come to the conclusion that it would be better
> > to provide an API call for getting filenames in the testsuite rather
> > than expecting test scripts to use variables.  API calls can be
> > aliased back into a master interpreter, while variable namespaces
> > are separate between interpreters.
> >     
>
> In principle, I like this idea.
>
> It's difficult to properly control an API when users have direct
> access to internal variables of the test framework.

If test scripts are ever moved to slave interpreters, the internal 
variables will disappear.  Similar results will occur if/when DejaGnu 
code is moved into Tcl namespaces (although the "exported" variables 
could remain globals in that case).  Moving DejaGnu into namespaces 
would greatly reduce the effort required to write a test script; 
currently, writing test scripts can feel like tap-dancing in a 
minefield:  even seemingly generic names like "text" can be (and if 
certain libraries are loaded that one is) global variables on whose 
values DejaGnu depends for correct operation.  Tcl 8 has namespaces; we 
should use them to lower the barrier to entry for using DejaGnu.  
(Moving the DejaGnu core into namespaces is on my local TODO list.  
Importing namespaced procedures into the global namespace will provide 
backwards compatibility.  Procedures not actually part of the API can be 
deprecated in this way as well:  the global version produces a 
deprecation warning but passes the call into the relevant namespace.)

>  Deprecating
> $subdir is going to be difficult (*), but perhaps we could do
> something like adding another runtest option that helps the
> maintainers of testsuites to find and remove deprecated features (for
> example, by not setting $subdir and catching the error as it
> propagates up to runtest.exp).
>
> * The GCC testsuite uses $subdir extensively and I'm sure other
> testsuites do, too.
>   

What?  Deprecating a variable looks easy, with a bit more 
infrastructure:  set a read trace on that variable and record any 
accesses from outside the DejaGnu core.  After printing the summary, 
emit a warning if any deprecated variables or procedures were used.  In 
verbose mode, also list where the variable was accessed.

A goal is that the API call be usable as a "drop-in" replacement:  
search/replace "$srcdir/$subdir" to "[testsuite file -source -test]" and 
"$objdir/$subdir" to "[testsuite file -build -test]" should be an easy 
and correct, but perhaps sub-optimal, migration.


-- Jacob