Cover extern functions safe

[michielp1807]

Continuation of #231

[codecov]

Codecov Report

❌ Patch coverage is 63.63636% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/dictBuilder/cover.rs	63.63%	12 Missing ⚠️

Flag	Coverage Δ
test-aarch64-apple-darwin	31.83% <63.63%> (-1.19%)	⬇️
test-aarch64-unknown-linux-gnu	30.67% <63.63%> (+0.06%)	⬆️
test-i686-unknown-linux-gnu	30.75% <63.63%> (+0.07%)	⬆️
test-x86_64-unknown-linux-gnu	32.56% <63.63%> (-0.56%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
lib/dictBuilder/fastcover.rs	76.41% <ø> (-2.46%)	⬇️
lib/dictBuilder/zdict.rs	32.19% <ø> (-1.67%)	⬇️
lib/dictBuilder/cover.rs	77.76% <63.63%> (-2.96%)	⬇️

... and 7 files with indirect coverage changes

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