encoding/json: Unintuitive behavior when using custom UnmarshalText

[glooms]

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

$ go version
go version go1.14.2 linux/amd64

Does this issue reproduce with the latest release?

Yes, it even seems like it was introduced somewhere between go1.13.9 and go1.14.2.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/qlik/.cache/go-build"
GOENV="/home/qlik/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/qlik/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/snap/go/5646"
GOSUMDB="off"
GOTMPDIR=""
GOTOOLDIR="/snap/go/5646/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build785744259=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I was trying to Unmarshal a JSON body containing \n into a map[String]string where String is TextUnmarshaler:

type String string

func (s *String) UnmarshalText(text []byte) error {
	*s = String(text)
	return nil
}

JSON body:

{
        "Pizza": "Pizza is yummy.\nIt is very yummy.",
        "Apple": "Apples are also yummy."
}

An example can be found here: https://play.golang.org/p/V7qY2khOcgH

Note, my key issue is the difference in behavior between the two maps in the playground example.

What did you expect to see?

A normal map without escaped quotes. Which is the result of using a map[string]string instead of a map[String]string.

What did you see instead?

Escaped quotes in the map keys. As if the key wasn't properly tokenized.

[mvdan]

This sounds like a duplicate of #38105, which has a fix in master that will be backported for 1.14.3.

[mvdan]

I can confirm that the tests from https://play.golang.org/p/V7qY2khOcgH pass on master, so this is a duplicate of the issue above. Follow #38106 for the backport to 1.14.3.

[glooms]

Thanks @mvdan