use checked addition to not panic in debug build

[Skgland]

used checked addition so this does not panic in debug builds

related to issue #870

not sure if #870 is completely resolved as there are other comments indicating a possible overflow condition that I did not understand and as such did not fix

[Skgland]

not sure if #870 is completely resolved as there are other comments indicating a possible overflow condition that I did not understand and as such did not fix

I think the line I was refering to is fine:
min_code_point - code_point > (u32::MAX - delta) / (processed + 1)

min_code_point should be lager than code_point due to the iterator filter c >= code_point as such this can't underflow on min_code_point - code_point

u32::MAX - delta cannot underflow either as delta can't be larger than u32:MAX

process + 1 can't overflow as process < input_length per the while condition

process + 1 is not 0 as process is unsigned, so no division by zero

[Skgland]

Restructured changes and moved test to the idna creat where it belongs in my opinion.

• The first commit fixes the line endings of debug_metadata/README.md as it was always considered dirty and prevented me from rebasing otherwise.
• The second commit adds the test, fails without the third commit.
• The third and last commit fixed the panic in debug builds due to overflow.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (e39c9a2) 81.81% compared to head (336623e) 81.84%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #877      +/-   ##
==========================================
+ Coverage   81.81%   81.84%   +0.03%     
==========================================
  Files          20       20              
  Lines        3514     3531      +17     
==========================================
+ Hits         2875     2890      +15     
- Misses        639      641       +2     

Files	Coverage Δ
idna/src/punycode.rs	85.44% <100.00%> (+0.44%)	⬆️
idna/tests/punycode.rs	80.39% <78.94%> (-0.86%)	⬇️

... and 1 file with indirect coverage changes

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[Skgland]

Fixed added test to not increase msrv beyond 1.56 (I think this change also increases readability of the test) and fixed unrelated clippy lint.
Ready for review again.

[Skgland]

Ok, now the rebase should be fixed.

[valenting]

Thank you for the fix. I really appreciate it.