float::from_str returns 0 for one space, and NaN for multiple spaces

[mbrubeck]

float::from_str(" ") (the input is a string of two space characters) returns NaN in Rust. It should return 0.0.

float::from_str(" ") (with just one space character) returns 0.0.

There is a test in stdtest/float.rs that should have caught this bug, but it is falsely passing because (NaN == 0.0) is true (#1083).

[brson]

Are we sure that spaces should parse? uint::from_str doesn't look like it parses space (actually it looks like it might do something crazy).

[mbrubeck]

Good question. For comparison, atof in C/C++, new Number(str) in JavaScript, and Double.valueOf(str) in Java all allow leading and trailing whitespace.

However, Rust's implementation is definitely not designed to do so, so it seems like an accident that it allows a single space in some cases. It should be changed to either allow or disallow any amount of leading and trailing space.

[brson]

That sounds like good precedent to me. We should probably make sure they allow all whitespace characters then (as defined in char::is_whitespace)

[mbrubeck]

Some more quirks:

float::from_str("e") yields zero, which I think is unintentional.

float::from_str(".") yields zero too, which is intentional and documented but seems like it might be a bad idea. . is not a valid floating-point literal, and any code that passes it to from_str seems likely to be a mistake.

[mbrubeck]

Fixed by #1103