Re: [PATCH v1 1/1] git diff --quiet exits with 1 on clean tree with CRLF conversions

["Torsten Bögershausen" <tboegi@web.de>]

On 2017-03-01 22:25, Mike Crowe wrote:
> On Wednesday 01 March 2017 at 18:04:44 +0100, tboegi@web.de wrote:
>> From: Junio C Hamano <gitster@pobox.com>
>>
>> git diff --quiet may take a short-cut to see if a file is changed
>> in the working tree:
>> Whenever the file size differs from what is recorded in the index,
>> the file is assumed to be changed and git diff --quiet returns
>> exit with code 1
>>
>> This shortcut must be suppressed whenever the line endings are converted
>> or a filter is in use.
>> The attributes say "* text=auto" and a file has
>> "Hello\nWorld\n" in the index with a length of 12.
>> The file in the working tree has "Hello\r\nWorld\r\n" with a length of 14.
>> (Or even "Hello\r\nWorld\n").
>> In this case "git add" will not do any changes to the index, and
>> "git diff -quiet" should exit 0.
>>
>> Add calls to would_convert_to_git() before blindly saying that a different
>> size means different content.
>>
>> Reported-By: Mike Crowe <mac@mcrowe.com>
>> Signed-off-by: Torsten Bögershausen <tboegi@web.de>
>> ---
>> This is what I can come up with, collecting all the loose ends.
>> I'm not sure if Mike wan't to have the Reported-By with a
>> Signed-off-by ?
>> The other question is, if the commit message summarizes the discussion
>> well enough ?
>>
>> diff.c                    | 18 ++++++++++++++----
>>  t/t0028-diff-converted.sh | 27 +++++++++++++++++++++++++++
>>  2 files changed, 41 insertions(+), 4 deletions(-)
>>  create mode 100755 t/t0028-diff-converted.sh
>>
>> diff --git a/diff.c b/diff.c
>> index 051761b..c264758 100644
>> --- a/diff.c
>> +++ b/diff.c
>> @@ -4921,9 +4921,10 @@ static int diff_filespec_check_stat_unmatch(struct diff_filepair *p)
>>  	 *    differences.
>>  	 *
>>  	 * 2. At this point, the file is known to be modified,
>> -	 *    with the same mode and size, and the object
>> -	 *    name of one side is unknown.  Need to inspect
>> -	 *    the identical contents.
>> +	 *    with the same mode and size, the object
>> +	 *    name of one side is unknown, or size comparison
>> +	 *    cannot be depended upon.  Need to inspect the
>> +	 *    contents.
>>  	 */
>>  	if (!DIFF_FILE_VALID(p->one) || /* (1) */
>>  	    !DIFF_FILE_VALID(p->two) ||
>> @@ -4931,7 +4932,16 @@ static int diff_filespec_check_stat_unmatch(struct diff_filepair *p)
>>  	    (p->one->mode != p->two->mode) ||
>>  	    diff_populate_filespec(p->one, CHECK_SIZE_ONLY) ||
>>  	    diff_populate_filespec(p->two, CHECK_SIZE_ONLY) ||
>> -	    (p->one->size != p->two->size) ||
>> +
>> +	    /*
>> +	     * only if eol and other conversions are not involved,
>> +	     * we can say that two contents of different sizes
>> +	     * cannot be the same without checking their contents.
>> +	     */
>> +	    (!would_convert_to_git(p->one->path) &&
>> +	     !would_convert_to_git(p->two->path) &&
>> +	     (p->one->size != p->two->size)) ||
>> +
>>  	    !diff_filespec_is_identical(p->one, p->two)) /* (2) */
>>  		p->skip_stat_unmatch_result = 1;
>>  	return p->skip_stat_unmatch_result;
>> diff --git a/t/t0028-diff-converted.sh b/t/t0028-diff-converted.sh
>> new file mode 100755
>> index 0000000..3d5ab95
>> --- /dev/null
>> +++ b/t/t0028-diff-converted.sh
>> @@ -0,0 +1,27 @@
>> +#!/bin/sh
>> +#
>> +# Copyright (c) 2017 Mike Crowe
>> +#
>> +# These tests ensure that files changing line endings in the presence
>> +# of .gitattributes to indicate that line endings should be ignored
>> +# don't cause 'git diff' or 'git diff --quiet' to think that they have
>> +# been changed.
>> +
>> +test_description='git diff with files that require CRLF conversion'
>> +
>> +. ./test-lib.sh
>> +
>> +test_expect_success setup '
>> +	echo "* text=auto" >.gitattributes &&
>> +	printf "Hello\r\nWorld\r\n" >crlf.txt &&
>> +	git add .gitattributes crlf.txt &&
>> +	git commit -m "initial"
>> +'
>> +
>> +test_expect_success 'quiet diff works on file with line-ending change that has no effect on repository' '
>> +	printf "Hello\r\nWorld\n" >crlf.txt &&
>> +	git status &&
>> +	git diff --quiet
>> +'
>> +
>> +test_done
> 
> Hi Torsten,
> 
> Thanks for investigating this.
> 
> I think that you've simplified the test to the point where it doesn't
> entirely prove the fix. Although you test the case where the file has
> changed size, you don't test the case where it hasn't.
> 
> Unfortunately that was the part of my test that could only reproduce the
> problem with the sleeps. Maybe someone who understands how the cache works
> fully could explain an alternative way to force the cache not to be used.
> 
> Also, I think I've found a behaviour change with this fix. Consider:
> 
>  echo "* text=auto" >.gitattributes
>  printf "Hello\r\nWorld\r\n" >crlf.txt
That should give
"Hello\nWorld\n" in the index:

git add .gitattributes crlf.txt
warning: CRLF will be replaced by LF in ttt/crlf.txt.
The file will have its original line endings in your working directory.
tb@mac:/tmp/ttt> git commit -m "initial"
[master (root-commit) 354f657] initial
 2 files changed, 3 insertions(+)
 create mode 100644 ttt/.gitattributes
 create mode 100644 ttt/crlf.txt
tb@mac:/tmp/ttt> git ls-files --eol
i/lf    w/lf    attr/text=auto          .gitattributes
i/lf    w/crlf  attr/text=auto          crlf.txt
tb@mac:/tmp/ttt>

>  git add .gitattributes crlf.txt
>  git commit -m "initial"
> 
>  printf "\r\n" >>crlf.txt
> 
> With the above patch, both "git diff" and "git diff --quiet" report that
> there are no changes. Previously Git would report the extra newline
> correctly.
Wait a second.
Which extra newline "correctly" ?

The "git diff" command is about the changes which will be done to the index.
Regardless if you have any of these in the working tree on disk:

"Hello\nWorld\n"
"Hello\nWorld\r\n"
"Hello\r\nWorld\n"
"Hello\r\nWorld\r\n"

"git status" and "git diff --quiet"
should not report any changes.

So I don't know if there is a mis-understanding about "git diff" on your side,
or if I miss something.