Re: [gfortran,patch] Fix PR libfortran/23262 (on mingw32)

[Brooks Moses <bmoses at stanford dot edu>]

FX Coudert wrote:
> > This patch is likely to do interesting things on Cygwin, which has an 
> > option (at install time) to switch between DOS and Unix newlines.
> >
> > According to my cursory understanding of how this works [1], if DOS mode 
> > is selected at install (or, more particularly, when the disk is mounted; 
> > it's a mount option), Cygwin uses the text-mode or binary-mode switch to 
> > decide whether or not to translate the line endings from DOS-mode (on 
> > disk) to Unix-mode (as seen by the program).
> >
> > My guess is that the result of this patch will be to "freeze" the 
> > newline handling on Cygwin to the setting that was active at compile 
> > time, rather than allowing it to adapt to the current system settings. 
> > For distributed binaries, this means the end user's settings would get 
> > completely ignored.
>
> I'm not sure how this works either, but from the FAQ link you posted, it 
> seems clear that only a few people use the mount switch. Plus, I do 
> think that specifying binary mode in the code does override the user 
> option (the opposite behaviour doesn't seem to make sense to me).

What wasn't clear from that FAQ link is that, while few people use the 
mount switch directly, there's a checkbox in the Cygwin install program 
to choose DOS or Unix line endings -- and, unless I'm mistaken, that 
checkbox sets up a default for how "mount" is called for the disks when 
the computer first boots.  So the switch is effectively being used by 
everyone who chooses the "DOS" option at install time.

Specifying binary mode appears to override the user option, yes.  What 
I'm thinking is that, when a gfortran-compiled program is creating a 
text file, it may not be appropriate to override the user option -- 
because, if we do, a Cygwin user may not get the line ending type that 
they want.

The reason that I say this will be "interesting" [1] is that I'm pretty 
sure your compile-time switch will return different results depending on 
the way Cygwin is set on the compiling computer.  And thus Paul T.'s 
setting on his computer -- rather than anything in the gfortran code or 
in the Cygwin code -- will determine the line endings for everyone who 
uses his compiled binaries.  (In practice, this is probably not a 
serious problem, but it's going to be a pain to track down if it becomes 
one, unless there's a comment about it somewhere obvious.)

I may have a chance to poke at this a bit and confirm some of this 
experimentally in the next couple of weeks; if I do, I'll report back.

- Brooks


[1] In the sense of the "may you live in interesting times" curse....