encoding/json: marshaling can drop .0 for floats

[0x0elliot]

What version of Go are you using (go version)? 1.19

$ go version
1.19

Does this issue reproduce with the latest release? Yes

What did you do?

This bug led to this: opensearch-project/opensearch-go#386

Here is the go.dev/play package: https://go.dev/play/p/lw648QN2w6Y

What did you expect to see?

It is however formatted to be: {"float_value":5}

This can cause weird type errors that would become hard to find. Let's fix this.

What did you see instead?

Expected the JSON to be formatted to: {"float_value":5.00} (since the value at hand is float)

I want to solve this issue myself. It looks like an easy fix. Please point me to the right direction so that I can close this myself for the next issue.

[0x0elliot]

I will try debugging this and following up:

go/src/encoding/json/encode.go

Line 159 in eb832af

func Marshal(v any) ([]byte, error) {

[seankhliao]

cc @mvdan @dsnet

[seankhliao]

Duplicate of #42246

[0x0elliot]

i disagree with the decisions there. it's important to maintain the .0's with the json.Marshal method because of the reason that JSON is used very prominently with systems that don't necessarily deal with types the same way.

as i demonstrated earlier, this leads to weird outcomes. types are not dealt with similarly everywhere, and it's nice for the library to acknowledge and help with that. what do you think? @seankhliao

[seankhliao]

as the comments in the linked issue mention, we've decided to align with how JavaScript handles numbers #42246 (comment)

[mvdan]

Like @seankhliao says, there are ways to precisely control how JSON numbers will be encoding and decoding to JSON, e.g. https://pkg.go.dev/encoding/json#Number or a custom marshaler/unmarshaler.

Also note that your original example seems a bit confusing. The float64 value 5.00 does not have two trailing zeros "as a string". You can notice that, for example, 5.0 == 5.000 is true, because they are both exactly the same float64 value, and not strings.

[0x0elliot]

hey @mvdan!

thanks for the reply. so:

1. don't worry about my confusing example. but i am glad you folks got the point.
2. you're actually correct. it's better to deal with how js deals with JSON. no matter how i hate how it deals with those things.

3. Backing up my last point that I made, fuck javascript.