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cmd/go2go: cannot use make(map[int]X) (value of type map[int]X) as map[int]X value in struct literal #39982

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arl opened this issue Jul 1, 2020 · 10 comments
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@arl
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@arl arl commented Jul 1, 2020

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

$ go version
go version devel +d014fca6d4 Wed Jul 1 20:30:10 2020 +0000 linux/amd64

Does this issue reproduce with the latest release?

It does with latest commit of the dev.go2go experimental branch: d014fca

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

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/aurelien/.cache/go-build"
GOENV="/home/aurelien/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/aurelien/godev/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/aurelien/godev"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/aurelien/dev/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/aurelien/dev/go/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-build789085526=/tmp/go-build -gno-record-gcc-switches"

What did you do?

A bit of context: I'm currently experimenting with the generics draft by trying to use it to develop a generics cache library.
I compacted the code into a single-file reproducer to make debugging easier but the actual code imports various packages, among which the list package of the dev.go2go source tree (generic replacement for container/list).

The original cache is based off a simple map where the value is a *list.Element(*entry(K).

package main

type (
	Element(type TElem) struct{}

	entry(type K comparable) struct{}

	Cache(type K comparable) struct {
		data map[K]*Element(*entry(K))
	}
)

func main() {
	_ = Cache(int){
		data: make(map[int](*Element(*entry(int)))), // cannot use make(map[int](*Element(*entry(int)))) (value of type map[int]*Element(*entry(int))) as map[int]*Element(*entry(int)) value in struct literal
	}
}

It does the same on the playground: https://go2goplay.golang.org/p/qoMgsPA5ifd

What did you expect to see?

a successful compilation since the provided map is, AFAICT, of the same type as the Cache.data type.

What did you see instead?

The error reported above:

cannot use make(map[int](*Element(*entry(int)))) (value of type map[int]*Element(*entry(int))) as map[int]*Element(*entry(int)) value in struct literal
@arl
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@arl arl commented Jul 1, 2020

It seems the translator sees 2 types whereas there's only one.

package main

type (
	Element(type TElem) struct{}

	entry(type K comparable) struct{}

	Cache(type K comparable) struct {
		data map[K]*Element(*entry(K))
	}
)

func main() {
	_ = Cache(int){}
	_ = make(map[int](*Element(*entry(int))))
}

gives:

# play
./prog.go2:6: instantiate୦୦Element୦୮1main୮aentry୮8int୮9 redeclared in this block
	previous declaration at ./prog.go2:10

playground: https://go2goplay.golang.org/p/B-cdj3yBgAw

Both errors (the one in the top post and this one) might be 2 faces of the same coin. In case they aren't let me know if I should open a different issue. Thanks

@arl arl changed the title cmd/go2go: cannot use make(map[int](*X) (value of type map[int]*X) as map[int]*X value in struct literal cmd/go2go: cannot use make(map[int]X) (value of type map[int]X) as map[int]X value in struct literal Jul 1, 2020
@ianlancetaylor ianlancetaylor added this to the Unreleased milestone Jul 1, 2020
@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jul 1, 2020

This seems like a failure in the type checker. At least, I don't see why it shouldn't work.

@griesemer
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@griesemer griesemer commented Jul 1, 2020

Definitely a type-checker failure.

@gopherbot
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@gopherbot gopherbot commented Jul 2, 2020

Change https://golang.org/cl/240737 mentions this issue: [dev.go2go] go/types: fix computation of type hash

gopherbot pushed a commit that referenced this issue Jul 2, 2020
Fixes #39982.

Change-Id: I4e7b52c34bf8df63f2063dc2504a8125ca7585a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/240737
Reviewed-by: Robert Griesemer <gri@golang.org>
@griesemer
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@griesemer griesemer commented Jul 2, 2020

Fixed on dev.go2go.

@griesemer griesemer closed this Jul 2, 2020
@arl
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@arl arl commented Jul 2, 2020

I just tested with 85ed317 and now both listing (top and 2nd comments of this issue) give the same error:

$ go tool go2go run issue39982.go2
# command-line-arguments
./issue39982.go2:25: instantiate୦୦Element୦୮1main୮aentry୮8int୮9 redeclared in this block
        previous declaration at ./issue39982.go2:29
/home/aurelien/dev/go/bin/go [run issue39982.go] failed: exit status 2

Let me know whether you prefer a new issue for this.

@griesemer
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@griesemer griesemer commented Jul 2, 2020

@arl, thanks for this. I admit I only tested type-checking for this case. Reopening.

@griesemer griesemer reopened this Jul 2, 2020
@griesemer
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@griesemer griesemer commented Jul 2, 2020

@ianlancetaylor Not sure if this is still a type-checker issue or a translator issue at this point.

@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jul 3, 2020

Thanks. Translator is fixed on dev.go2go branch.

@gopherbot
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@gopherbot gopherbot commented Jul 3, 2020

Change https://golang.org/cl/240899 mentions this issue: [dev.go2go] go/go2go: resolve pointers in sameType

gopherbot pushed a commit that referenced this issue Jul 3, 2020
Fixes #39982

Change-Id: Ieb33381716662b44464104e0073a52ab5c19b7c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/240899
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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