strconv: document ParseFloat's special cases (nan, inf)

[johnbalvin]

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

go version go1.12 windows/amd64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\TATA\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\TATA\Documents\go
set GOPROXY=
set GORACE=
set GOROOT=C:\Go
set GOTMPDIR=
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\TATA\AppData\Local\Temp\go-build125692270=/tmp/go-build -gno-record-gcc-switches

What did you do?

Convert some string values to float

package main

package main

import (
	"fmt"
	"strconv"
	"log"
)

func main() {
	s, err := strconv.ParseFloat("nan", 32)
	if err != nil {
		log.Printf(" err: %s: ",err)
	}
	fmt.Printf("%T, %v\n", s, s)

}

What did you expect to see?

Error showing in the console because NaN is not a number

What did you see instead?

NaN

[randall77]

This is intentional behavior. I think we just need to mention it in the docs.

[gopherbot]

Change https://golang.org/cl/174204 mentions this issue: strconv: Document ParseFloat's special cases #30990.

[msoedov]

Change has been successfully cherry-picked as 203b80a by

[gopherbot]

Change https://golang.org/cl/179738 mentions this issue: strconv: document handling of NaN and ±Inf