[Patch, Fortran] PR 40881: warn for obsolescent features

[Daniel Kraft]

Hi Janus,

Janus Weil wrote:
> Hi all,
> 
> the Fortran 90 standard lists nine "obsolescent" f77 features, which
> continue to be supported in f90, but may be deleted in the future.
> Therefore their usage is discouraged by the standard. Currently, we
> only warn about two of them (arithmetic if and assumed length
> character functions). This patch adds warnings for four more:
> 
> * alternate return
> * computed goto
> * statement functions
> * old-style character lengths ["character*..." instead of "character(...)"]
> 
> That leaves three obsolescent features, which are not warned about:
> 
> * shared DO termination
> * DATA statements among executable statements
> * fixed form source
> 
> These may be added later.
> 
> The patch is technically very simple, but has a rather large impact on
> the testsuite, since lots of test cases use old-style character
> lengths. For most of them I just added -std=legacy. But some already
> use -std=f95, so I had to change the character lengths to f90 style or
> add a dg-warning. For the already-implemented obsolescent warnings I
> changed the message to unify it with the new ones, so I also had to
> change some dg-warnings in the testsuite.
> 
> Regtested on x86_64-unknown-linux-gnu. Ok for trunk?

I like this update on warnings, and indeed ok for trunk with me.

Thanks for working on this!

Daniel

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