stat() and tilde prefix (was bad bash tab completion)

Christopher Faylor
Thu Feb 7 16:26:00 GMT 2013

On Thu, Feb 07, 2013 at 05:23:22PM +0100, Corinna Vinschen wrote:
>On Feb  7 17:10, Thomas Wolff wrote:
>> Am 07.02.2013 16:30, schrieb Eric Blake:
>> >...
>> >
>> >...
>> >the fact that cygwin's handling of .. is not POSIX-compliant.  I think a
>> >better fix would be to change file_exists() itself instead of adding a
>> >misnamed wrapper function; then bashline.c wouldn't even need patching.
>> >  The string 'tilde' need not even be in the patch; what you are really
>> >after is a function that says that if '..' is found within a string
>> >being probed for existence, then add an additional check to see if the
>> >prefix of that string exists as a directory.
>> >
>> >But I don't mind experimenting with the idea - it remains to be seen
>> >whether people will complain that bash is noticeably slower because it
>> >takes time to double-check instead of rely on cygwin's non-POSIX
>> >shortcut.  And the slowdown would only be on paths containing a '..'; I
>> >would NOT be checking for symlinks (even though symlinks containing ..
>> >are also being interpreted in a non-POSIX manner, it is much more
>> >expensive to second-guess if you have to check every name for being a
>> >symlink than it is to just check for literal ..).
>> Do I interpret correctly that you talk about bash filename completion here?
>> Referring to,
>> I'd like to point out that while this ".." thing is a cygwin bug, or
>> known downside as Corinna says,
>> the same issue occurs on Linux precisely with filename completion
>> which isn't consistent there either.
>> So it would be "over-fixing" to handle that specifically in bash.
>> On the other hand, considering again this "downside":
>> If the core cygwin filesystem function would follow this approach,
>> simply checking for an occurrence of ".." first before resolving the
>> filename,
>> wouldn't that be an acceptable fix without inappropriate penalty?
>You don't know what you're asking for (can of worms, etc.)
>This is some kind of chicken egg problem.
>- The path must be normalized, otherwise we can't reliably convert
>  the POSIX path prefix to a Windows pathname.
>- Only after converting to a Windows path, we can perform file checks.
>- Rinse and repeat.
>Also, the path normalization is performed in an entirely distinct
>function from the mount point conversion, and this in turn is another
>function than the path function handling symlinks and devices.
>Changing that requires to implement the path conversion functionality
>almost from scratch.  Given the age of some of these functions, I'd
>like to have done that for a long time, but I'm constantly shying away
>since I don't want to break what is working today.  There's, of course,
>still the aforementioned chicken-egg problem.

What she said.


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