BUG: git-check-ignore documentation doesn't come close to describing what it really does

BUG: git-check-ignore documentation doesn't come close to describing what it really does

[Britton Kerin]

It begins:

       For each pathname given via the command-line or from a file via
--stdin, check whether
       the file is excluded by .gitignore (or other input files to the
exclude mechanism) and output
       the path if it is excluded.

In fact it just reports matches from .gitignore etc:

     $ cat .gitignore
     *.o
     !*.dont_ignore
     $ ls
     bar.o.dont_ignore  foo.o
     $ git check-ignore -v -n *
     .gitignore:2:!*.dont_ignore bar.o.dont_ignore
     .gitignore:1:*.o foo.o
     $ # Even more confusing without -v -n:
     $ git check-ignore *
     bar.o.dont_ignore
     foo.o

The EXIT STATUS section is even more wrong:

     EXIT STATUS
            0
                One or more of the provided paths is ignored.

            1
                None of the provided paths are ignored.

            128
                A fatal error was encountered.

but:

     $ if git check-ignore foo.o.dont_ignore; then echo exited true;
else echo exited false; fi
     foo.o.dont_ignore
     exited true
     $

IMO the behavior of git-check-ignore is the correct and useful
behavior and the documentation should simply be fixed to reflect the
fact that it just lists matching entries rather than wrongly claiming
that it returns the overall result of the ignore calculation.

Britton

Re: BUG: git-check-ignore documentation doesn't come close to describing what it really does

[Elijah Newren]

Hi,

Thanks for the report.

On Tue, Jul 12, 2022 at 4:34 PM Britton Kerin <britton.kerin@gmail.com> wrote:
>
> It begins:
>
>        For each pathname given via the command-line or from a file via
> --stdin, check whether
>        the file is excluded by .gitignore (or other input files to the
> exclude mechanism) and output
>        the path if it is excluded.

I suspect we're having an aliasing problem that you're not
recognizing.  "ignored" and "excluded" are used interchangeably, note
that patterns from the $GIT_DIR/info/exclude files and patterns from
the file pointed to by core.excludesFile are also lumped together with
the patterns from all the .gitignore files (see the gitignore manual
page).  Further, the internal code refers to them all as "excludes"
not as "ignores".

(And then we adopted the same syntax for sparse checkouts, except we
used it to mark things that should be included, and we referred
everyone to the documentation about "excludes" to learn the format for
what to "include".  Ugh.)

>
> In fact it just reports matches from .gitignore etc:

Yes, it outputs the paths that are excluded, as the documentation
said.  Perhaps there's a way to reword it to make this clearer?  I
don't think we can get rid of the alias given the fact that
$GIT_DIR/info/exclude and core.excludesFile are hard-coded and must be
kept for backward compatibility.  But suggestions to improve the
wording would be great.

Maybe it'd be as simple as replacing "is excluded" with "matches an
ignore/exclude rule"?

>      $ cat .gitignore
>      *.o
>      !*.dont_ignore
>      $ ls
>      bar.o.dont_ignore  foo.o
>      $ git check-ignore -v -n *
>      .gitignore:2:!*.dont_ignore bar.o.dont_ignore
>      .gitignore:1:*.o foo.o
>      $ # Even more confusing without -v -n:
>      $ git check-ignore *
>      bar.o.dont_ignore
>      foo.o
>
> The EXIT STATUS section is even more wrong:
>
>      EXIT STATUS
>             0
>                 One or more of the provided paths is ignored.

"is ignored", meaning "matches an ignore/exclude rule".  Perhaps we
should update the docs with that textual change?

>             1
>                 None of the provided paths are ignored.

and replace "are ignored" with the same phrase here?

>
>             128
>                 A fatal error was encountered.
>
> but:
>
>      $ if git check-ignore foo.o.dont_ignore; then echo exited true;
> else echo exited false; fi
>      foo.o.dont_ignore

So the filename matched one of the rules, causing the filename to be printed.

>      exited true

and it returned a 0 exit status, since one of the provided paths was
ignored, as documented.

>      $
>
> IMO the behavior of git-check-ignore is the correct and useful
> behavior

I'm with you here.

> and the documentation should simply be fixed

Yes, I agree it's easy to misinterpret.  Would my suggested changes help?

> to reflect the
> fact that it just lists matching entries rather than wrongly claiming
> that it returns the overall result of the ignore calculation.

I think I understood where the problems were in the documentation that
could lead to misinterpretations in the other two cases you mentioned
earlier in your email, but I don't understand this one.  Even the
first sentence you quoted included the phrase that it could "output
the path", so I'm not sure where you think it claims that it'd return
the overall result of the ignore calculation.  Could you point out
what in the document led you to believe it was claiming this?  Maybe I
could suggest wording improvements for it as well.  Or maybe you have
some.

Re: BUG: git-check-ignore documentation doesn't come close to describing what it really does

[Junio C Hamano]

Elijah Newren <newren@gmail.com> writes:

> I suspect we're having an aliasing problem that you're not
> recognizing.  "ignored" and "excluded" are used interchangeably, note
> that patterns from the $GIT_DIR/info/exclude files and patterns from
> the file pointed to by core.excludesFile are also lumped together with
> the patterns from all the .gitignore files (see the gitignore manual
> page).  Further, the internal code refers to them all as "excludes"
> not as "ignores".

All true.

> Yes, it outputs the paths that are excluded, as the documentation
> said.  Perhaps there's a way to reword it to make this clearer?  I
> don't think we can get rid of the alias given the fact that
> $GIT_DIR/info/exclude and core.excludesFile are hard-coded and must be
> kept for backward compatibility.  But suggestions to improve the
> wording would be great.
>
> Maybe it'd be as simple as replacing "is excluded" with "matches an
> ignore/exclude rule"?

I smell a continuation of 7ec8125f (check-ignore: fix documentation
and implementation to match, 2020-02-18), which appears in 2.26 and
later (the way the negative entries in the ignore/exclude mechanism
gets handled has changed in Git 2.26, and the documentation has been
updated).

"Is excluded" is perfectly fine, I think.  The first use of that
verb in the documentation should be a bit more careful, e.g. "is
excluded (aka ignored)" or something.

>> IMO the behavior of git-check-ignore is the correct and useful
>> behavior
>
> I'm with you here.

Yup, with the old "huh?" fixed in Git 2.26 (which was there simply
because check-ignore was not used to be a serious end-user facing
program but was more of a debugging aid), I think the behaviour of
the command we have today is what we want.

>> and the documentation should simply be fixed
>
> Yes, I agree it's easy to misinterpret.  Would my suggested changes help?
>
>> to reflect the
>> fact that it just lists matching entries rather than wrongly claiming
>> that it returns the overall result of the ignore calculation.
>
> I think I understood where the problems were in the documentation that
> could lead to misinterpretations in the other two cases you mentioned
> earlier in your email, but I don't understand this one.  Even the
> first sentence you quoted included the phrase that it could "output
> the path", so I'm not sure where you think it claims that it'd return
> the overall result of the ignore calculation.  Could you point out
> what in the document led you to believe it was claiming this?  Maybe I
> could suggest wording improvements for it as well.  Or maybe you have
> some.

It does return *the* matching entry that decided the path's fate.

    $ (echo '/no-such-*'; echo '!/no-such-*') >>.git/info/exclude
    $ git check-ignore -v no-such-directory; echo $?
    .git/info/exclude:14:!/no-such-*	no-such-directory
    0

Exit status section needs a bit more work.  It used to be OK to say
"success (0) is returned when we found a path that is ignored", but
these days, it is not whether there are ignored paths in the input.

It signals if we found an entry in the list of exclude/ignore
patterns that actively affects the path's fate.  In our project, if
we ask the fate of hello.c

    $ git check-itnore -v hello.c; echo $?
    1

because we do not say explicitly that .c files are usually tracked
sources.  If we did this:

    $ echo >>.git/info/exclude '!*.c'

to explicitly say that .c files are never ignored, it changes the
picture:

    $ git check-itnore -v hello.c; echo $?
    .git/info/exclude:15:!*.c	hello.c
    0

Re: BUG: git-check-ignore documentation doesn't come close to describing what it really does

[Britton Leo Kerin]

Junio C Hamano <gitster@pobox.com> writes:

> Elijah Newren <newren@gmail.com> writes:
>
> > I suspect we're having an aliasing problem that you're not
> > recognizing.  "ignored" and "excluded" are used interchangeably, note
> > that patterns from the $GIT_DIR/info/exclude files and patterns from
> > the file pointed to by core.excludesFile are also lumped together with
> > the patterns from all the .gitignore files (see the gitignore manual
> > page).  Further, the internal code refers to them all as "excludes"
> > not as "ignores".
>
> All true.

I wasn't surprised that 'ignoread' and 'excluded' are used interchangably,
that's not the problem.

> > Yes, it outputs the paths that are excluded, as the documentation
> > said.  Perhaps there's a way to reword it to make this clearer?  I
> > don't think we can get rid of the alias given the fact that
> > $GIT_DIR/info/exclude and core.excludesFile are hard-coded and must be
> > kept for backward compatibility.  But suggestions to improve the
> > wording would be great.
> >
> > Maybe it'd be as simple as replacing "is excluded" with "matches an
> > ignore/exclude rule"?
>
> I smell a continuation of 7ec8125f (check-ignore: fix documentation
> and implementation to match, 2020-02-18), which appears in 2.26 and
> later (the way the negative entries in the ignore/exclude mechanism
> gets handled has changed in Git 2.26, and the documentation has been
> updated).
>
> "Is excluded" is perfectly fine, I think.  The first use of that
> verb in the documentation should be a bit more careful, e.g. "is
> excluded (aka ignored)" or something.

I think replacing with "matches an ignore/exclude rule" is prefereable since
that's what's actually going on.  It's still a bit unfortunate since the
ignore/exclude terms are potentially confusing in the presence of dont-ignore
(!) rules, but it seems likely that people running check-ignore are looking to
sort out something complicated and are probably aware of negative rules, and
anyway they get a ! to clue them in :)

Adding some explanation to the first use of "excluded" would in principle solve
the problem by itself and give licence to use the term however you want, but to
be honest I'm not sure I would have read that paragraph carefully enough to get
the idea.  It still seems better to me to use different language each time it
comes up in the page.

> >> IMO the behavior of git-check-ignore is the correct and useful
> >> behavior
> >
> > I'm with you here.
>
> Yup, with the old "huh?" fixed in Git 2.26 (which was there simply
> because check-ignore was not used to be a serious end-user facing
> program but was more of a debugging aid), I think the behaviour of
> the command we have today is what we want.
>
> >> and the documentation should simply be fixed
> >
> > Yes, I agree it's easy to misinterpret.  Would my suggested changes help?
> >
> >> to reflect the
> >> fact that it just lists matching entries rather than wrongly claiming
> >> that it returns the overall result of the ignore calculation.
> >
> > I think I understood where the problems were in the documentation that
> > could lead to misinterpretations in the other two cases you mentioned
> > earlier in your email, but I don't understand this one.  Even the
> > first sentence you quoted included the phrase that it could "output
> > the path", so I'm not sure where you think it claims that it'd return
> > the overall result of the ignore calculation.  Could you point out
> > what in the document led you to believe it was claiming this?  Maybe I
> > could suggest wording improvements for it as well.  Or maybe you have
> > some.
>
> It does return *the* matching entry that decided the path's fate.
>
>     $ (echo '/no-such-*'; echo '!/no-such-*') >>.git/info/exclude
>     $ git check-ignore -v no-such-directory; echo $?
>     .git/info/exclude:14:!/no-such-*	no-such-directory
>     0

Good point: it's not exactly a full query either.

If it would be welcome and hasn't already been done I could rewrite this page
to be clearer without adding or changing much.

Britton

Re: BUG: git-check-ignore documentation doesn't come close to describing what it really does

[Junio C Hamano]

Britton Leo Kerin <britton.kerin@gmail.com> writes:

>> "Is excluded" is perfectly fine, I think.  The first use of that
>> verb in the documentation should be a bit more careful, e.g. "is
>> excluded (aka ignored)" or something.
>
> I think replacing with "matches an ignore/exclude rule" is prefereable since
> that's what's actually going on.

Unfortunately, it is only half of what's actually going on, isn't
it?  If the last match is with a positive entry, then it is excluded
(aka ignored).  If the last match is with a negative entry, then it
is not excluded (and not shown without "-v").  That is demonstrated
by the example:

>> It does return *the* matching entry that decided the path's fate.
>>
>>     $ (echo '/no-such-*'; echo '!/no-such-*') >>.git/info/exclude
>>     $ git check-ignore -v no-such-directory; echo $?
>>     .git/info/exclude:14:!/no-such-*	no-such-directory
>>     0

and

    $ git check-ignore no-such-directory; echo $?
    1

i.e. with "-v", the output can give enough clue to the user if the
match was with positive or negative entry, but without "-v", the
exit status reports if the given path is "excluded (aka ignored)".
In the above case, the last entry that matches the path
"no-such-directory" is a negative entry, so the path is not
excluded, hence there is no output (as documented, excluded paths
are output).

If we remove the last line from .git/info/exclude, then the
transcript would become:

    $ git check-ignore no-such-directory; echo $?
    no-such-directory
    0
    $ git check-ignore -v no-such-directory; echo $?
    .git/info/exclude:13:/no-such-* no-such-directory
    0

As the last entry that matches the path is a positive entry in this
case, the path is excluded and it is shown in the output without
"-v" and the command exits with success (i.e. is excluded).

Here is a rough attempt to clarify what I found was unclear in the
current documentation.

Thanks.

 Documentation/git-check-ignore.txt | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git c/Documentation/git-check-ignore.txt w/Documentation/git-check-ignore.txt
index 2892799e32..a5491386cf 100644
--- c/Documentation/git-check-ignore.txt
+++ w/Documentation/git-check-ignore.txt
@@ -16,7 +16,8 @@ DESCRIPTION
 -----------
 
 For each pathname given via the command-line or from a file via
-`--stdin`, check whether the file is excluded by .gitignore (or other
+`--stdin`, check whether the file is excluded (aka "ignored"---these
+words are used interchangeably) by .gitignore (or other
 input files to the exclude mechanism) and output the path if it is
 excluded.
 
@@ -31,11 +32,12 @@ OPTIONS
 
 -v, --verbose::
 	Instead of printing the paths that are excluded, for each path
-	that matches an exclude pattern, print the exclude pattern
-	together with the path.  (Matching an exclude pattern usually
+	that matches an exclude pattern (or more), print the exclude
+	pattern that decides if the path is excluded or not excluded,
+	together with the path.  Matching an exclude pattern usually
 	means the path is excluded, but if the pattern begins with "`!`"
 	then it is a negated pattern and matching it means the path is
-	NOT excluded.)
+	NOT excluded.
 +
 For precedence rules within and between exclude sources, see
 linkgit:gitignore[5].
@@ -65,10 +67,12 @@ linkgit:gitignore[5].
 OUTPUT
 ------
 
-By default, any of the given pathnames which match an ignore pattern
+By default, any of the given pathnames which are excluded (aka ignored)
 will be output, one per line.  If no pattern matches a given path,
 nothing will be output for that path; this means that path will not be
-ignored.
+ignored.  If the pattern that matched the path is a negative one (i.e.
+prefixed with "`!`"), the path is not excluded and nothing is output
+for the path.
 
 If `--verbose` is specified, the output is a series of lines of the form: