Re: [PATCH 01/10] diff --color-moved=zerba: fix alternate coloring

> "Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> Subject: Re: [PATCH 01/10] diff --color-moved=zerba: fix alternate coloring
> 
> Zerba?

>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>
>> b0a2ba4776 ("diff --color-moved=zebra: be stricter with color
>> alternation", 2018-11-23) sought to avoid using the alternate colors
>> unless there are two adjacent moved blocks of the same
>> sign. Unfortunately it contains two bugs that prevented it from fixing
>> the problem properly. Firstly `last_symbol` is reset at the start of
>> each iteration of the loop losing the symbol of the last line and
>> secondly when deciding whether to use the alternate color it should be
>> checking if the current line is the same sign of the last line, not a
>> different sign. The combination of the two errors means that we still
>> use the alternate color when we should do but we also use it when we
>> shouldn't. This is most noticable when using
>> --color-moved-ws=allow-indentation-change with hunks like
>>
>> -this line gets indented
>> +    this line gets indented
>>
>> where the post image is colored with newMovedAlternate rather than
>> newMoved. While this does not matter much, the next commit will change
>> the coloring to be correct in this case, so lets fix the bug here to
>> make it clear why the output is changing and add a regression test.
>>
>> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>> ---
>>   diff.c                     |  4 +--
>>   t/t4015-diff-whitespace.sh | 72 ++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 74 insertions(+), 2 deletions(-)
>>
>> diff --git a/diff.c b/diff.c
>> index 52c791574b71..cb068f8258c0 100644
>> --- a/diff.c
>> +++ b/diff.c
>> @@ -1142,6 +1142,7 @@ static void mark_color_as_moved(struct diff_options *o,
>>   	struct moved_block *pmb = NULL; /* potentially moved blocks */
>>   	int pmb_nr = 0, pmb_alloc = 0;
>>   	int n, flipped_block = 0, block_length = 0;
>> +	enum diff_symbol last_symbol = 0;
>>   
>>   
>>   	for (n = 0; n < o->emitted_symbols->nr; n++) {
>> @@ -1149,7 +1150,6 @@ static void mark_color_as_moved(struct diff_options *o,
>>   		struct moved_entry *key;
>>   		struct moved_entry *match = NULL;
>>   		struct emitted_diff_symbol *l = &o->emitted_symbols->buf[n];
>> -		enum diff_symbol last_symbol = 0;
>>   
>>   		switch (l->s) {
>>   		case DIFF_SYMBOL_PLUS:
>> @@ -1214,7 +1214,7 @@ static void mark_color_as_moved(struct diff_options *o,
>>   			}
>>   
>>   			if (adjust_last_block(o, n, block_length) &&
>> -			    pmb_nr && last_symbol != l->s)
>> +			    pmb_nr && last_symbol == l->s)
>>   				flipped_block = (flipped_block + 1) % 2;
>>   			else
>>   				flipped_block = 0;
>> diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
>> index 2c13b62d3c65..920114cd795c 100755
>> --- a/t/t4015-diff-whitespace.sh
>> +++ b/t/t4015-diff-whitespace.sh
>> @@ -1442,6 +1442,78 @@ test_expect_success 'detect permutations inside moved code -- dimmed-zebra' '
>>   	test_cmp expected actual
>>   '
>>   
>> +test_expect_success 'zebra alternate color is only used when necessary' '
>> +	cat >old.txt <<-\EOF &&
>> +	line 1A should be marked as oldMoved newMovedAlternate
>> +	line 1B should be marked as oldMoved newMovedAlternate
>> +	unchanged
>> +	line 2A should be marked as oldMoved newMovedAlternate
>> +	line 2B should be marked as oldMoved newMovedAlternate
>> +	line 3A should be marked as oldMovedAlternate newMoved
>> +	line 3B should be marked as oldMovedAlternate newMoved
>> +	unchanged
>> +	line 4A should be marked as oldMoved newMovedAlternate
>> +	line 4B should be marked as oldMoved newMovedAlternate
>> +	line 5A should be marked as oldMovedAlternate newMoved
>> +	line 5B should be marked as oldMovedAlternate newMoved
>> +	line 6A should be marked as oldMoved newMoved
>> +	line 6B should be marked as oldMoved newMoved
>> +	EOF
>> +	cat >new.txt <<-\EOF &&
>> +	  line 1A should be marked as oldMoved newMovedAlternate
>> +	  line 1B should be marked as oldMoved newMovedAlternate
>> +	unchanged
>> +	  line 3A should be marked as oldMovedAlternate newMoved
>> +	  line 3B should be marked as oldMovedAlternate newMoved
>> +	  line 2A should be marked as oldMoved newMovedAlternate
>> +	  line 2B should be marked as oldMoved newMovedAlternate
>> +	unchanged
>> +	  line 6A should be marked as oldMoved newMoved
>> +	  line 6B should be marked as oldMoved newMoved
>> +	    line 4A should be marked as oldMoved newMovedAlternate
>> +	    line 4B should be marked as oldMoved newMovedAlternate
>> +	  line 5A should be marked as oldMovedAlternate newMoved
>> +	  line 5B should be marked as oldMovedAlternate newMoved
>> +	EOF
>> +	test_expect_code 1 git diff --no-index --color --color-moved=zebra \
>> +		 --color-moved-ws=allow-indentation-change \
>> +		 old.txt new.txt >output &&
>> +	grep -v index output | test_decode_color >actual &&
>> +	cat >expected <<-\EOF &&
>> +	<BOLD>diff --git a/old.txt b/new.txt<RESET>
>> +	<BOLD>--- a/old.txt<RESET>
>> +	<BOLD>+++ b/new.txt<RESET>
>> +	<CYAN>@@ -1,14 +1,14 @@<RESET>
>> +	<BOLD;MAGENTA>-line 1A should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;MAGENTA>-line 1B should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 1A should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 1B should be marked as oldMoved newMovedAlternate<RESET>
>> +	 unchanged<RESET>
>> +	<BOLD;MAGENTA>-line 2A should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;MAGENTA>-line 2B should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;BLUE>-line 3A should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;BLUE>-line 3B should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 3A should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 3B should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;YELLOW>+<RESET><BOLD;YELLOW>  line 2A should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;YELLOW>+<RESET><BOLD;YELLOW>  line 2B should be marked as oldMoved newMovedAlternate<RESET>
>> +	 unchanged<RESET>
>> +	<BOLD;MAGENTA>-line 4A should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;MAGENTA>-line 4B should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;BLUE>-line 5A should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;BLUE>-line 5B should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;MAGENTA>-line 6A should be marked as oldMoved newMoved<RESET>
>> +	<BOLD;MAGENTA>-line 6B should be marked as oldMoved newMoved<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 6A should be marked as oldMoved newMoved<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 6B should be marked as oldMoved newMoved<RESET>
>> +	<BOLD;YELLOW>+<RESET><BOLD;YELLOW>    line 4A should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;YELLOW>+<RESET><BOLD;YELLOW>    line 4B should be marked as oldMoved newMovedAlternate<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 5A should be marked as oldMovedAlternate newMoved<RESET>
>> +	<BOLD;CYAN>+<RESET><BOLD;CYAN>  line 5B should be marked as oldMovedAlternate newMoved<RESET>
>> +	EOF
>> +	test_cmp expected actual
>> +'
>> +
>>   test_expect_success 'cmd option assumes configured colored-moved' '
>>   	test_config color.diff.oldMoved "magenta" &&
>>   	test_config color.diff.newMoved "cyan" &&