Replace lazy_static dependency in chain crate with once_cell

[philmartin2525]

Addresses #213

This PR replaces usage of the lazy_static! macro with the once_cell::sync::Lazy type. This accomplishes the same goals as lazy_static! by lazily initializing global data. once_cell has the following advantages over lazy_static:

• once_cell has seen more recent active development
  • once_cell = "1.9.0" was released about 1 month ago
  • lazy_static = "1.4.0" was released over 2 years ago
• once_cell functionality is in the current nightly build of Rust - tracking issue

Other comparisons between the two libraries

• All-time downloads (according to crates.io):
  • once_cell = ~40 million
  • lazy_static = ~70 million
• Github contributors/stars
  • once_cell = 34 contributors, 931 stars
  • lazy_static = 47 contributors, 1.3k stars

[dr-orlovsky]

Thank you for this proposal! BTW it does not closes #213, since the idea was not to use any form of static and try to convert that into a constant expressions (I didn't wrote that in the description of the issue, sorry). It was not that lazy_static is bad, it is just we would like to reduce the size of dependency tree - and "frequently updated" sounds a bit scary for a project that aims ossification (as a client-side-validated library).

Nevertheless this is a clear improvement over what we have now. Especially I like the part that once_cell is going to become a part of the rust itself and with time we will be able to remove this from the dependencies.

Will merge once CI will finish running.

[dr-orlovsky]

Sorry, it seems it requires reformatting + rebase on the master (according to the merge policy of the repo). Can you do it please?

[codecov]

Codecov Report

Merging #220 (0617fcc) into master (64d727f) will increase coverage by 1.6%.
The diff coverage is 87.5%.

❗ Current head 0617fcc differs from pull request most recent head d6e621a. Consider uploading reports for the commit d6e621a to get more accurate results

@@           Coverage Diff            @@
##           master    #220     +/-   ##
========================================
+ Coverage    68.4%   70.0%   +1.6%     
========================================
  Files           5       5             
  Lines        1273    1226     -47     
========================================
- Hits          871     858     -13     
+ Misses        402     368     -34     

Impacted Files	Coverage Δ
chain/src/lib.rs	87.7% <87.5%> (+0.1%)	⬆️
src/lib.rs	35.1% <0.0%> (-12.1%)	⬇️

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[philmartin2525]

I updated the description to indicate this doesn't satisfy #213 . Next time I will get clarification.

I will check the formatting and other issues.

[philmartin2525]

The formatting error should be fixed with the latest commit:

• cargo fmt --all -- --check passed locally
• cargo clippy --workspace --all-features failed in the CI checks, fails locally with latest commit, as does the latest master branch

As for rebasing onto master, the output of rebase is Current branch replace-lazy-static-with-once-cell is up to date. Am I missing something about the merge policy?

[philmartin2525]

As for rebasing onto master, the output of rebase is Current branch replace-lazy-static-with-once-cell is up to date. Am I missing something about the merge policy?

I see what you mean now. I was pulling from the wrong remote. It should be cleanly rebased now.