Compilation failure (cannot use struct [...] as struct [...])

[klauspost]

What version of Garble and Go are you using?

λ garble version
mvdan.cc/garble v0.10.1

Build settings:
      -buildmode exe
       -compiler gc
  DefaultGODEBUG panicnil=1
     CGO_ENABLED 1
          GOARCH amd64
            GOOS windows
         GOAMD64 v1

λ go version
go version go1.21.0 windows/amd64

What environment are you running Garble on?

go env Output

λ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=e:\temp\gocache
set GOENV=C:\Users\klaus\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=e:\gopath\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=e:\gopath
set GOPRIVATE=
set GOPROXY=https://goproxy.dev,direct
set GOROOT=C:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.21.0
set GCCGO=gccgo
set GOAMD64=v1
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=e:\gopath\src\github.com\klauspost\compress\go.mod
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=e:\temp\wintemp\go-build3567242259=/tmp/go-build -gno-record-gcc-switches

What did you do?

Compile this code:

package x

import "encoding/json"

func JSON() []byte {
	x := struct {
		TotalUncompressed int64 `json:"total_uncompressed"`
		TotalCompressed   int64 `json:"total_compressed"`
		Offsets           []struct {
			CompressedOffset   int64 `json:"compressed"`
			UncompressedOffset int64 `json:"uncompressed"`
		} `json:"offsets"`
		EstBlockUncomp int64 `json:"est_block_uncompressed"`
	}{
		TotalUncompressed: 1,
		TotalCompressed:   2,
		EstBlockUncomp:    3,
	}
	for _, v := range []int64{1, 2, 3} {
		x.Offsets = append(x.Offsets, struct {
			CompressedOffset   int64 `json:"compressed"`
			UncompressedOffset int64 `json:"uncompressed"`
		}{CompressedOffset: v, UncompressedOffset: v})
	}
	b, _ := json.MarshalIndent(x, "", "  ")
	return b
}

What did you expect to see?

λ go build repro.go

λ 

What did you see instead?

λ garble build repro.go
# command-line-arguments
HfGnX1.go:1: cannot use struct{MTsXn_rKxas int64 `json:"compressed"`; VJ6N6dh8 int64 `json:"uncompressed"`}{…} (value of type struct{MTsXn_rKxas int64 "json:\"compressed\""; VJ6N6dh8 int64 "json:\"uncompressed\""}) as struct{CompressedOffset int64 "json:\"compressed\""; UncompressedOffset int64 "json:\"uncompressed\""} value in argument to append
exit status 2
exit status 1

λ 

Seems like only right side is garbled.

[mvdan]

We have a few of these bugs, like #685, and I'm trying to figure them out. Thanks for minifying a reproducer :)

[klauspost]

For anyone else, the solution is to just extract the type:

	type offset struct {
		CompressedOffset   int64 `json:"compressed"`
		UncompressedOffset int64 `json:"uncompressed"`
	}

This will get you building until the compatibility issue is resolved.

[pagran]

I think this bug has two triggers:

Anon structs:

package main

import "encoding/json"

func JSON() []byte {
	x := struct {
		A []struct {
			A int64
		}
		B struct {
			B int64
		}
	}{}

	x.A = append(x.A, struct{ A int64 }{A: int64(0)})
	x.B = struct{ B int64 }{B: int64(0)}
	b, _ := json.MarshalIndent(x, "", "  ")
	return b
}

package main

import "encoding/json"

type ASTR struct {
	A int64
}

type BSTR struct {
	B int64
}

func JSON() []byte {
	x := struct {
		A []ASTR `json:"offsets"`
		B BSTR
	}{}

	x.A = append(x.A, struct{ A int64 }{A: int64(0)}) // [*ssa.ChangeType     ] t8 = changetype ASTR <- struct{A int64} (t5)
	x.B = struct{ B int64 }{B: int64(0)} // [*ssa.ChangeType     ] t16 = changetype BSTR <- struct{B int64} (t14)
	b, _ := json.MarshalIndent(x, "", "  ")
	return b
}

I think the second case can be fixed by analyzing ssa.ChangeType instruction

[mvdan]

I think the second case can be fixed by analyzing ssa.ChangeType instruction

Indeed that's where I'm going with a couple of local patches I've got in progress. I only got stuck since, for some reason, the behavior seems to be somewhat random. I also sent a PR to update to Go 1.21 in the meantime, and got an unexpected timeout that I can't reproduce locally 😵‍💫