add -i: close some regression test gaps

[dscho]

While re-implementing git add -i and git add -p in C, I tried to make sure that there is test coverage for all of the features I convert from Perl to C, to give me some confidence in the correctness from running the test suite both with GIT_TEST_ADD_I_USE_BUILTIN=true and with GIT_TEST_ADD_I_USE_BUILTIN=false.

However, I discovered that there are a couple of gaps. This patch series intends to close them.

The first patch might actually not be considered a gap by some: it basically removes the need for the TTY prerequisite in the git add -i tests to verify that the output is colored all right. This change is rather crucial for me, though: on Windows, where the conversion to a built-in shows the most obvious benefits, there are no pseudo terminals (yet), therefore git.exe cannot work with them (even if the MSYS2 Perl interpreter used by Git for Windows knows about some sort of pty emulation). And I really wanted to make sure that the colors work on Windows, as I personally get a lot out of those color cues.

The patch series ends by addressing two issues that are not exactly covering testing gaps:

• While adding a test case, I noticed that git add -p exited with success when it could not even generate a diff. This is so obviously wrong that I had to fix it right away (I noticed, actually, because my in-progress built-in git add -p failed, and the Perl version did not), and I used the same test case to verify that this is fixed once and for all.

• While working on covering those test gaps, I noticed a problem in an early version of the built-in version of git add -p where the git apply --allow-overlap mode failed to work properly, for little reason, and I fixed it real quick.

  It would seem that the --allow-overlap function is not only purposefully under-documented, but also purposefully under-tested, probably to discourage its use. I do not quite understand the aversion to that option, but I did not feel like I should put up a battle here, so I did not accompany this fix with a new test script.

  In the end, the built-in version of git add -p does not use the --allow-overlap function at all, anyway. Which should make everybody a lot happier.

Changes since v1:

• Added a paragraph to the commit message talking about the reason why the --allow-overlap patch needs to loosen up only at the beginning but not at the end of the file.

[dscho]

/submit

[gitgitgadget]

Submitted as pull.172.git.1575637705.gitgitgadget@gmail.com

[gitgitgadget]

On the Git mailing list, Junio C Hamano wrote (reply to this):

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> Yes, yes, this is supposed to be only a band-aid option for `git add -p`
> not Doing The Right Thing. But as long as we carry the `--allow-overlap`
> option, we might just as well get it right.

It probably depends on the definition of "right", where it may not
even exist (otherwise it wouldn't be a band-aid but be a real
feature) ;-)

> This fixes the case where one hunk inserts a line before the first line,
> and is followed by a hunk whose context overlaps with the first one's
> and which appends a line at the end.

The in-code comment makes me wonder if we need to further loosen the
check in the other direction, though.  What makes begin more special
than end?  Can a hunk be seen that pretends to extend to the end but
no longer does because there was an overlapping hunk that has been
wiggled in?

>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  apply.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/apply.c b/apply.c
> index f8a046a6a5..720a631eaa 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -2661,6 +2661,16 @@ static int find_pos(struct apply_state *state,
>  	unsigned long backwards, forwards, current;
>  	int backwards_lno, forwards_lno, current_lno;
>  
> +	/*
> +	 * When running with --allow-overlap, it is possible that a hunk is
> +	 * seen that pretends to start at the beginning (but no longer does),
> +	 * and that *still* needs to match the end. So trust `match_end` more
> +	 * than `match_beginning`.
> +	 */
> +	if (state->allow_overlap && match_beginning && match_end &&
> +	    img->nr - preimage->nr != 0)
> +		match_beginning = 0;
> +
>  	/*
>  	 * If match_beginning or match_end is specified, there is no
>  	 * point starting from a wrong line that will never match and

[gitgitgadget]

On the Git mailing list, Johannes Schindelin wrote (reply to this):

Hi Junio,

On Fri, 6 Dec 2019, Junio C Hamano wrote:

> "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
> writes:
>
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > Yes, yes, this is supposed to be only a band-aid option for `git add -p`
> > not Doing The Right Thing. But as long as we carry the `--allow-overlap`
> > option, we might just as well get it right.
>
> It probably depends on the definition of "right", where it may not
> even exist (otherwise it wouldn't be a band-aid but be a real
> feature) ;-)

Indeed. My hope is that we can get rid of it once the scripted
`git-add--interactive.perl` is removed in favor of the built-in add -i/-p.
This is a long way off, of course.

> > This fixes the case where one hunk inserts a line before the first line,
> > and is followed by a hunk whose context overlaps with the first one's
> > and which appends a line at the end.
>
> The in-code comment makes me wonder if we need to further loosen the
> check in the other direction, though.  What makes begin more special
> than end?  Can a hunk be seen that pretends to extend to the end but
> no longer does because there was an overlapping hunk that has been
> wiggled in?

The beginning is more special than the end because it is associated with
the line number 1. The end line number is flexible already.

There is another difference: after splitting hunks, the first hunk is
applied first, and may render the line numbers of succeeding hunks
incorrect. The same is not true for the last hunk: it cannot render the
preceding hunks' line numbers incorrect, as it has not been applied yet.

I think that's why `--allow-overlap` works with this patch when adding
lines both to the beginning and to the end after splitting a single hunk.

Ciao,
Dscho

> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >  apply.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/apply.c b/apply.c
> > index f8a046a6a5..720a631eaa 100644
> > --- a/apply.c
> > +++ b/apply.c
> > @@ -2661,6 +2661,16 @@ static int find_pos(struct apply_state *state,
> >  	unsigned long backwards, forwards, current;
> >  	int backwards_lno, forwards_lno, current_lno;
> >
> > +	/*
> > +	 * When running with --allow-overlap, it is possible that a hunk is
> > +	 * seen that pretends to start at the beginning (but no longer does),
> > +	 * and that *still* needs to match the end. So trust `match_end` more
> > +	 * than `match_beginning`.
> > +	 */
> > +	if (state->allow_overlap && match_beginning && match_end &&
> > +	    img->nr - preimage->nr != 0)
> > +		match_beginning = 0;
> > +
> >  	/*
> >  	 * If match_beginning or match_end is specified, there is no
> >  	 * point starting from a wrong line that will never match and
>

[gitgitgadget]

On the Git mailing list, Junio C Hamano wrote (reply to this):

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> The beginning is more special than the end because it is associated with
> the line number 1. The end line number is flexible already.

Yeah, we do not insist "the lineno must be X" at the end like we do
at the beginning, but we still insist "there cannot be no post
context if we are adding at the end" just like there cannot be any
pre context for a patch that adds at the beginning, no?

> There is another difference: after splitting hunks, the first hunk is
> applied first, and may render the line numbers of succeeding hunks
> incorrect. The same is not true for the last hunk: it cannot render the
> preceding hunks' line numbers incorrect, as it has not been applied yet.

This truly may make quite a difference, especially because the hunks
are applied in order.

Thanks.

[gitgitgadget]

On the Git mailing list, Johannes Schindelin wrote (reply to this):

Hi Junio,

On Fri, 6 Dec 2019, Junio C Hamano wrote:

> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>
> > The beginning is more special than the end because it is associated with
> > the line number 1. The end line number is flexible already.
>
> Yeah, we do not insist "the lineno must be X" at the end like we do
> at the beginning, but we still insist "there cannot be no post
> context if we are adding at the end" just like there cannot be any
> pre context for a patch that adds at the beginning, no?

True.

> > There is another difference: after splitting hunks, the first hunk is
> > applied first, and may render the line numbers of succeeding hunks
> > incorrect. The same is not true for the last hunk: it cannot render the
> > preceding hunks' line numbers incorrect, as it has not been applied yet.
>
> This truly may make quite a difference, especially because the hunks
> are applied in order.

I think you're right, I fooled myself into believing that the line number
1 is special, but the real culprit is that the second hunk is applied
_after_ the first one may have changed the (overlapping) context. The same
is not true for the second-to-last hunk: it will always be applied before
the end of the file can possibly become no longer the end of the file.

I'll try to think up a concise paragraph about this, and stick it into the
commit message.

Ciao,
Dscho

[gitgitgadget]

This branch is now known as js/add-i-a-bit-more-tests.

[gitgitgadget]

This patch series was integrated into pu via git@6ee74d4.

[gitgitgadget]

On the Git mailing list, Junio C Hamano wrote (reply to this):

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
> index f43634102e..5db6432e33 100755
> --- a/t/t3701-add-interactive.sh
> +++ b/t/t3701-add-interactive.sh
> @@ -530,7 +530,7 @@ test_expect_success 'diff.algorithm is passed to `git diff-files`' '
>  	>file &&
>  	git add file &&
>  	echo changed >file &&
> -	git -c diff.algorithm=bogus add -p 2>err &&
> +	test_must_fail git -c diff.algorithm=bogus add -p 2>err &&

Makes sense.

>  	test_i18ngrep "error: option diff-algorithm accepts " err
>  '

[gitgitgadget]

This patch series was integrated into pu via git@0127f4d.

[gitgitgadget]

This patch series was integrated into pu via git@dd8604a.

[gitgitgadget]

This patch series was integrated into pu via git@e0fa0b1.

[gitgitgadget]

This patch series was integrated into pu via git@a762546.

[gitgitgadget]

This patch series was integrated into next via git@d7ffb75.

[gitgitgadget]

On the Git mailing list, SZEDER Gábor wrote (reply to this):

On Fri, Dec 06, 2019 at 01:08:20PM +0000, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <johannes.schindelin@gmx.de>
> 
> The TTY prerequisite is a rather heavy one: it not only requires Perl to
> work, but also the IO/Pty.pm module (with native support, and it
> requires pseudo terminals, too).
> 
> In particular, test cases marked with the TTY prerequisite would be
> skipped in Git for Windows' SDK.
> 
> In the case of `git add -p`, we do not actually need that big a hammer,
> as we do not want to test any functionality that requires a pseudo
> terminal; all we want is for the interactive add command to use color,
> even when being called from within the test suite.
> 
> And we found exactly such a trick earlier already: when we added a test
> case to verify that the main loop of `git add -i` is colored
> appropriately. Let's use that trick instead of the TTY prerequisite.

It's much more interesting _what_ that trick is than when it was
found.  Is it setting TERM=vt100, or is it setting both TERM=vt100 and
GIT_PAGER_IN_USE=true?  I'm inclined to think the latter, but I'm not
sure I interpreted the comment below right.

> +# This function uses a trick to manipulate the interactive add to use color:
> +# the `want_color()` function special-cases the situation where a pager was
> +# spawned and Git now wants to output colored text: to detect that situation,
> +# the environment variable `GIT_PAGER_IN_USE` is set. However, color is

Perhaps a s/is set/has to be set/ would have helped my interpreter,
dunno.

> +# suppressed despite that environment variable if the `TERM` variable
> +# indicates a dumb terminal, so we set that variable, too.
> +
> +force_color () {
> +	env GIT_PAGER_IN_USE=true TERM=vt100 "$@"
> +}

In any case, there are a couple of tests in other test scripts that
test color relying on the TTY prereq.  So maybe it would be worth to
make this into a "global" helper function by adding it to
'test-lib-functions.sh', so we can drop a few more prereqs.

OTOH, some of those other tests have descriptions like:

  t3203-branch-output.sh:test_expect_success TTY '%(color) present with tty'
  t7004-tag.sh:test_expect_success TTY '%(color) present with tty'

i.e. their description is specific about checking the behaviour with a
tty, so I'm not entirely sure.

[gitgitgadget]

On the Git mailing list, Jeff King wrote (reply to this):

On Mon, Dec 16, 2019 at 01:18:59PM +0100, SZEDER Gábor wrote:

> > And we found exactly such a trick earlier already: when we added a test
> > case to verify that the main loop of `git add -i` is colored
> > appropriately. Let's use that trick instead of the TTY prerequisite.
> 
> It's much more interesting _what_ that trick is than when it was
> found.  Is it setting TERM=vt100, or is it setting both TERM=vt100 and
> GIT_PAGER_IN_USE=true?  I'm inclined to think the latter, but I'm not
> sure I interpreted the comment below right.

It's both. GIT_PAGER_IN_USE tells Git not to bother checking isatty(),
and then TERM=vt100 is necessary to override test-lib's TERM=dumb
specifically for the color code.

> In any case, there are a couple of tests in other test scripts that
> test color relying on the TTY prereq.  So maybe it would be worth to
> make this into a "global" helper function by adding it to
> 'test-lib-functions.sh', so we can drop a few more prereqs.
> 
> OTOH, some of those other tests have descriptions like:
> 
>   t3203-branch-output.sh:test_expect_success TTY '%(color) present with tty'
>   t7004-tag.sh:test_expect_success TTY '%(color) present with tty'
> 
> i.e. their description is specific about checking the behaviour with a
> tty, so I'm not entirely sure.

Hmm. I have mixed feelings on this. I do like the simplicity of avoiding
test_terminal (which is unportable and has also contributed to some
confusing behavior in the past[1]). But it also takes us further away from
a real-world setup.

That might be OK for the tests you quoted above, if we're OK with
assuming the equivalence of isatty() and GIT_PAGER_IN_USE for the color
code (though we'd probably want to make sure that's tested _somewhere_).

But it obviously would not work for test-terminal callers that are
checking the pager behavior. And I suspect it may create other oddities;
e.g., a script which calls a sub-command that looks at GIT_PAGER_IN_USE,
even though the sub-command's output is going to a pipe. Though one
could argue that's a bug[2] (that could be triggered by _actually_
sending the script's output to pager).

If we're going to get rid of test-terminal.pl (and I would be happy
enough to see it go), I'd rather we mock things up at the isatty()
level, something like what I showed in:

  https://lore.kernel.org/git/20190524062724.GC25694@sigill.intra.peff.net/

That gives us a more realistic setup, and we could reliably use it
everywhere that test-terminal is used.

-Peff

[1] I had issues a while back with test-terminal's stdin feature being
    racy:

      https://lore.kernel.org/git/20190520125016.GA13474@sigill.intra.peff.net/

[2] Long ago I had a patch to make PAGER_IN_USE more careful by making
    sure that our pipe is the same as the pager pipe. It did (and does)
    work, but it would need some portability adjustments. I never
    bothered to follow up because it really does seem to be a pretty
    unlikely setup in practice. But if you're curious:

      https://lore.kernel.org/git/20150810052353.GB15441@sigill.intra.peff.net/

-Peff

[gitgitgadget]

This patch series was integrated into pu via git@011fc2e.

[gitgitgadget]

This patch series was integrated into next via git@011fc2e.

[gitgitgadget]

This patch series was integrated into master via git@011fc2e.

[gitgitgadget]

Closed via 011fc2e.