Core fuzz generation and tests of it

[prozacchiwawa]

This is a framework for accumulating arbitrary programs that fit some desired constraints or have desirable structure or properties. While it's possible to fuzz compilers with completely arbitrary programs, the vast majority of programs generated completely arbitrarily aren't meaningful enough to fully compile or fully execute.

This allows us to choose a middle ground where we can try to produce unexpected inputs for the compiler while ensuring

• We can know that the program is compilable
• We can force the program to exercise features under test
• We can know what the program is supposed to do before executing it so we can compare the result

[coveralls]

Pull Request Test Coverage Report for Build 8744268851

Details

• 111 of 117 (94.87%) changed or added relevant lines in 2 files are covered.
• 8 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 82.935%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/compiler/fuzz.rs	50	53	94.34%
src/compiler/sexp.rs	61	64	95.31%
<!--	Total:	111	117	94.87%	-->

Files with Coverage Reduction	New Missed Lines	%
src/compiler/sexp.rs	8	79.08%
<!--	Total:	8		-->

Totals
Change from base Build 8742161930:	0.04%
Covered Lines:	14925
Relevant Lines:	17996

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💛 - Coveralls