Fix Number.toExponential and Number.toFixed

[nrabulinski]

This Pull Request closes #1602.

It makes toExponential and toFixed methods on Number compliant with the specification.

One of the tests in toExponential currently fails. This is something that's blocked by rust-lang/rust#89493, unless we were to implement the exponential string algorithm ourselves.

[raskad]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	80,930	80,930	0
Passed	33,364	33,388	+24
Ignored	15,898	15,898	0
Failed	31,668	31,644	-24
Panics	0	0	0
Conformance	41.23%	41.26%	+0.03%

Fixed tests (24):

test/built-ins/Number/prototype/toFixed/S15.7.4.5_A1.4_T01.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toFixed/S15.7.4.5_A1.4_T01.js (previously Failed)
test/built-ins/Number/prototype/toFixed/range.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toFixed/range.js (previously Failed)
test/built-ins/Number/prototype/toFixed/S15.7.4.5_A1.3_T01.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toFixed/S15.7.4.5_A1.3_T01.js (previously Failed)
test/built-ins/Number/prototype/toFixed/S15.7.4.5_A1.3_T02.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toFixed/S15.7.4.5_A1.3_T02.js (previously Failed)
test/built-ins/Number/prototype/toExponential/return-abrupt-tointeger-fractiondigits-symbol.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/return-abrupt-tointeger-fractiondigits-symbol.js (previously Failed)
test/built-ins/Number/prototype/toExponential/this-is-0-fractiondigits-is-0.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/this-is-0-fractiondigits-is-0.js (previously Failed)
test/built-ins/Number/prototype/toExponential/range.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/range.js (previously Failed)
test/built-ins/Number/prototype/toExponential/this-is-0-fractiondigits-is-not-0.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/this-is-0-fractiondigits-is-not-0.js (previously Failed)
test/built-ins/Number/prototype/toExponential/return-abrupt-tointeger-fractiondigits.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/return-abrupt-tointeger-fractiondigits.js (previously Failed)
test/built-ins/Number/prototype/toExponential/infinity.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/infinity.js (previously Failed)
test/built-ins/Number/prototype/toExponential/undefined-fractiondigits.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/undefined-fractiondigits.js (previously Failed)
test/built-ins/Number/prototype/toExponential/tointeger-fractiondigits.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toExponential/tointeger-fractiondigits.js (previously Failed)

[raskad]

Regarding the one failing test; I think we should merge this without that one.

But we may have an easier solution that to fix the issues in std. We already use ryu-js crate that converts numbers to strings. Conveniently the repository for the crate is in the boa-dev org: https://github.com/boa-dev/ryu-js ;)

Without looking further into it, my idea would be to implement the functionality of num_to_exponential and num_to_exponential_with_precision there. @HalidOdat I think you probably know the most about this, do you think we should try to do that, or is ryu-js not the right place?

[raskad]

Looks good to me!

[jedel1043]

Just a small nitpick I have about the utility functions

[nrabulinski]

Actually I just realized that there's another case which isn't covered by any 262 test and that's (1.0).toExponential(), which should return 1e+0 but returned 1e0 for us 😄

[jedel1043]

Great work!

[jedel1043]

Actually I just realized that there's another case which isn't covered by any 262 test and that's (1.0).toExponential(), which should return 1e+0 but returned 1e0 for us 😄

Oh, that can be filed on the test262 repo