fix: use correct return value in bcf_get_format and bcf_get_info_values

[Marlin-Na]

According to the notes in htslib vcf header file:

Use the returned number of written values for accessing valid entries of dst, as ndst is only a
watermark that can be higher than the returned value, i.e. the end of dst can contain carry-over
values from previous calls to bcf_get_format_*() on lines with more values per sample.

I had a case that when accessing a format field of string type, even there was only one sample, I got two strings returned (albeit the second one was empty). With this change, the issue was fixed.

[coveralls]

Pull Request Test Coverage Report for Build 5327586180

• 31 of 37 (83.78%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.4%) to 79.758%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/bcf/record.rs	31	37	83.78%

Files with Coverage Reduction	New Missed Lines	%
src/bcf/record.rs	1	78.83%
src/bam/record.rs	4	76.31%

Totals
Change from base Build 5324511866:	0.4%
Covered Lines:	2439
Relevant Lines:	3058

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💛 - Coveralls

[johanneskoester]

Can you please add one or two test cases which show that ret is the right thing to use and also works in case of multiple strings?

[dlaehnemann]

Another thing I noticed: It seems like we then simply have ret returned once as a usize and once as an i32. And indeed, most of the calls to these internal functions seem to use only one version. And in the other cases, one could simply cast it into the other type. So maybe just return Ok(Some(ret)) as is and then cast it to usize whenever that is necessary?

[Marlin-Na]

Looking at the code again. I think maybe an alternative fix is to change

rust-htslib/src/bcf/record.rs

Line 1473 in 261e3a3

self.data(htslib::BCF_HT_STR).map(|(n, _)| {

in Format reader to use ret instead of n.

The Info reader actually got it correct:

rust-htslib/src/bcf/record.rs

Line 1329 in 261e3a3

data.map(|(_, ret)| {

[Marlin-Na]

But float() and integer() in Format read also got it wrong. Yeah I think we should just use ret instead of n. I will implement the fix @dlaehnemann suggested.

rust-htslib/src/bcf/record.rs

Line 1455 in 261e3a3

self.data(htslib::BCF_HT_REAL).map(|(n, _)| {

[Marlin-Na]

I think this PR is ready for merging.