wip: datalog foreign function interface prototype

[divarvel]

This allows using external functions in datalog.

This makes it easy to provide custom logic without extending the spec for every use-case, at the expense of portability: behaviour is no longer guaranteed to be consistent cross languages, and some languages won’t be able to support it at all (for instance JS as of now).

Todo:

• feature-gating if possible (does it make sense? since it will still impact protobuf serialization)
• samples (if we consider it part of the spec?)

Open questions:

• protobuf enum index for the FFI variants (contiguous or not?)
• should function names be interned as well? they are currently not

Code coverage should be improved by adding samples

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #228 will not alter performance

_{Comparing ffi (a179587) with v5 (e59f41d)}

Summary

✅ 12 untouched benchmarks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.54180% with 79 lines in your changes missing coverage. Please review.

Project coverage is 65.44%. Comparing base (796ba5d) to head (a179587). Report is 9 commits behind head on v5.

Files with missing lines	Patch %	Lines
biscuit-parser/src/builder.rs	0.00%	34 Missing :warning:
biscuit-auth/src/token/builder.rs	86.76%	18 Missing :warning:
biscuit-auth/src/format/convert.rs	74.13%	15 Missing :warning:
biscuit-auth/src/token/authorizer.rs	25.00%	6 Missing :warning:
biscuit-auth/src/datalog/expression.rs	90.90%	4 Missing :warning:
biscuit-auth/examples/testcases.rs	93.10%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##               v5     #228      +/-   ##
==========================================
+ Coverage   64.82%   65.44%   +0.62%     
==========================================
  Files          25       25              
  Lines        6502     6729     +227     
==========================================
+ Hits         4215     4404     +189     
- Misses       2287     2325      +38     

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🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests

[Geal]

that will be a great tool for future experimentation