Re: Git Test Coverage Report (Mon. Dec 9)

[Derrick Stolee <stolee@gmail.com>]

On 12/9/2019 1:23 PM, Derrick Stolee wrote:
> On 12/9/2019 1:10 PM, René Scharfe wrote:
>> Am 09.12.19 um 18:44 schrieb Derrick Stolee:
>>> On 12/9/2019 12:19 PM, Eric Sunshine wrote:
>>>> On Mon, Dec 9, 2019 at 12:11 PM René Scharfe <l.s.r@web.de> wrote:
>>>>> Am 09.12.19 um 16:36 schrieb Derrick Stolee:
>>>>>> René Scharfe  0bb313a5 xdiff: unignore changes in function context
>>>>>> xdiff/xemit.c
>>>>>> 0bb313a5 223)        xchp->i1 + xchp->chg1 <= s1 &&
>>>>>> 0bb313a5 224)        xchp->i2 + xchp->chg2 <= s2)
>>>>>> 0bb313a5 225) xchp = xchp->next;
>>>>>
>>>>> Hmm, line 223 *is* exercised by t4015.85.
>>>>
>>>> This, along with Dscho's[1] review of an earlier coverage report,
>>>> makes one wonder if there is some off-by-one error in the reporting
>>>> logic, such that it is reporting the wrong lines as not covered.
>>>
>>> This is definitely possible. I'll see if I can locate the bug in
>>> my report-generation code.
>>>
>>> However, line 222 is here [1]
>>>
>>> 	while (xchp != xch &&
>>>
>>> So if this is always false, then the rest of the while condition
>>> will not be tested, nor will the body (line 225: xchp = xchp->next;).
>>
>> 0bb313a5 also added lines 228 and 229, which are not in the report, so
>> xchp != xch must be true at least once (it is, in t4015.85).
>>
>> 222)				while (xchp != xch &&
>> 223)				       xchp->i1 + xchp->chg1 <= s1 &&
>> 224)				       xchp->i2 + xchp->chg2 <= s2)
>> 225)					xchp = xchp->next;
>> 226)
>> 227)				/* If so, show it after all. */
>> 228)				if (xchp != xch) {
>> 229)					xch = xchp;
> 
> Thanks for pointing out that context.
> 
> My guess is that gcov is marking the line as uncovered because the &&
> operator is on that line. I'm testing [1] by breaking style conventions
> and using the following:
> 
> 				while (xchp != xch
> 				       && xchp->i1 + xchp->chg1 <= s1
> 				       && xchp->i2 + xchp->chg2 <= s2)
> 					xchp = xchp->next;
> 
> [1] https://dev.azure.com/git/git/_build/results?buildId=1453

Confirmed:

target	fork/test-gcov
base	e0522318ac56aeb88f14e72ba2db25912e9972de


Uncovered code in 'target' not in 'base'
--------------------------------------------------------

xdiff/xemit.c
ddd5ad00 224)        && xchp->i2 + xchp->chg2 <= s2)

Commits introducing uncovered code:
Derrick Stolee	ddd5ad00 TEST: switch position of &&


For future reference: having the "&&" at the end of the
line will mark the line as uncovered if the right-hand
side of the && is uncovered. The same holds for other
short-circuit operators.

Thanks,
-Stolee