NaN handling broke in 1.0.6

[astraw]

What version of the csv crate are you using?

The problem arose in 6105a6a, which was released as 1.0.6.

Briefly describe the question, bug or feature request.

Not a number values of f64 ("NaN") are no longer serialized as "NaN" but rather an extreme value such as "2.696539702293474e308". I have not checked if this also affects f32.

Include a complete program demonstrating a problem.

Change the tutorial tutorial-write-serde-02.rs like this:

--- examples/tutorial-write-serde-02.rs	2019-04-29 01:50:05.089292433 +0200
+++ ../csv-nan-demo/src/main.rs	2019-04-29 02:03:24.364042987 +0200
@@ -1,3 +1,4 @@
+//tutorial-write-serde-02.rs
extern crate csv;
extern crate serde;
#[macro_use]
@@ -39,7 +40,7 @@
        city: "Oakman",
        state: "AL",
        population: None,
-        latitude: 33.7133333,
+        latitude: std::f64::NAN,
        longitude: -87.3886111,
    })?;

What is the observed behavior of the code above?

I now get the following output:

City,State,Population,Latitude,Longitude
Davidsons Landing,AK,,65.2419444,-165.2716667
Kenai,AK,7610,60.5544444,-151.2583333
Oakman,AL,,2.696539702293474e308,-87.3886111

Note the extreme latitude value for Oakman.

What is the expected or desired behavior of the code above?

whereas with the previous commit, I got:

City,State,Population,Latitude,Longitude
Davidsons Landing,AK,,65.2419444,-165.2716667
Kenai,AK,7610,60.5544444,-151.2583333
Oakman,AL,,NaN,-87.3886111

[astraw]

The documentation for ryu::Buffer::format says:

/// # Special cases
///
/// This function **does not** check for NaN or infinity. If the input
/// number is not a finite float, the printed representation will be some
/// correctly formatted but unspecified numerical value.
///
/// Please check [`is_finite`] yourself before calling this function, or
/// check [`is_nan`] and [`is_infinite`] and handle those cases yourself.
///
/// [`is_finite`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_finite
/// [`is_nan`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_nan
/// [`is_infinite`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_infinite

it looks like serialize_f32() and serialize_f64() for SeRecord in src/serializer.rs use this method but do not make this check. I think either the check should be made or lower-level functions, which do format NaN correctly, should be used. These lower level functions are f2s_buffered_n and d2s_buffered_n.

[BurntSushi]

I see. Yeah, I think doing the explicit check with is_finite/is_nan would be the best path forward here. The lower level functions look handy, but I'd much rather do the extra case analysis and avoid unsafe if we can get away with it.

I also filed an issue upstream to see about perhaps fixing this inside of ryu (or at least get a better understanding of the current design): dtolnay/ryu#12

[jesskfullwood]

I believe this issue can now be resolved simply by bumping ryu to 1.0.0.

[BurntSushi]

@jesskfullwood Awesome, thanks for the tip. I'll do the upgrade when I context switch back into this library, since there are a few other things I'd like to tidy up, and then do a 1.1.0 release. It's next on my list.