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encoding/json: custom type marshaling doesn't work for map values #55890

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friedrichsenm opened this issue Sep 27, 2022 · 2 comments
Open

encoding/json: custom type marshaling doesn't work for map values #55890

friedrichsenm opened this issue Sep 27, 2022 · 2 comments
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@friedrichsenm
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What version of Go are you using (go version)?

$ go version 1.16

Does this issue reproduce with the latest release?

Yes

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

go env Output
$ go env

GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/home/matt/.cache/go-build"

GOENV="/home/matt/.config/go/env"

GOEXE=""

GOEXPERIMENT=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GOMODCACHE="/home/matt/go/pkg/mod"

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

GOPATH="/home/matt/go"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/home/matt/sdk/go1.19.1"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/home/matt/sdk/go1.19.1/pkg/tool/linux_amd64"

GOVCS=""

GOVERSION="go1.19.1"

GCCGO="gccgo"

GOAMD64="v1"

AR="ar"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD="/home/matt/GitHub/relay_common/smm_api/go.mod"

GOWORK=""

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 -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2596506419=/tmp/go-build -gno-record-gcc-switches"

What did you do?

If you define custom marshaling/unmarshaling functions for a type, json.Marshal doesn't use them when the custom type is used as value in a map.

https://go.dev/play/p/uggz6OAQo_J

What did you expect to see?

I expect the custom type marshaling functions to be respected even when the custom type is a value in a map

What did you see instead?

JSON reverts to a default marshaling/unmarshaling function
@panjf2000 panjf2000 added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 27, 2022
@panjf2000
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cc @mvdan

@dsnet
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dsnet commented Sep 27, 2022

This is a known problem. It is related to but not quite identical to #33993 and #22967.

Fundamentally, the issue is that the "encoding/json" package has an non-addressable value on hand, and so it can't call a pointer method. There are ways to resolve this in the internal implementation of "json", but doing so has historically proven to be a breaking change.

@dsnet dsnet removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Sep 27, 2022
@dmitshur dmitshur added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Sep 27, 2022
@dmitshur dmitshur added this to the Backlog milestone Sep 27, 2022
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