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cmd/compile: implict dereference using constraints doesn't compile with -G=3 as expected #47713

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abraithwaite opened this issue Aug 15, 2021 · 6 comments
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cmd/compile: implict dereference using constraints doesn't compile with -G=3 as expected #47713

abraithwaite opened this issue Aug 15, 2021 · 6 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Go1.18

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

15:30:26 $ go version
go version devel go1.18-4d3cc847745 Thu Aug 12 20:22:27 2021 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes, on current HEAD of dev.typeparams.

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

go env Output
15:31:08 $ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/abraithwaite/.cache/go-build"
GOENV="/home/abraithwaite/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/abraithwaite/Projects/golang/pkg/mod"
GOOS="linux"
GOPATH="/home/abraithwaite/Projects/golang"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/abraithwaite/sdk/gotip"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/abraithwaite/sdk/gotip/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="devel go1.18-4d3cc847745 Thu Aug 12 20:22:27 2021 +0000"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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-build4018258502=/tmp/go-build -gno-record-gcc-switches"

What did you do? What did you expect to see? What did you see instead?

Using the following program, when compiling I expected an implicit de-reference of the method receiver:

https://github.com/abraithwaite/go-typeparams-issues/blob/master/bug-report-1/main.go

I expected no compilation error. This is what I saw instead:

15:32:18 $ go run -gcflags='-G=3' ./main.go
# command-line-arguments
<autogenerated>:1: cannot use .this (type *GenericSerializable[*main.SerDeString]) as type GenericSerializable[.shape.*uint8] in argument to GenericSerializable[.shape.*uint8].Send

I'm not sure why GenericSerializable is being passed as a pointer receiver instead of a value receiver as I've defined for .Send.

I saw this also: #47031 Maybe it's related? Seemed different enough to warrant opening this issue.
@mknyszek
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AFAIK dev.typeparams has been now merged into master, so I'm dropping that from the title.

Since this appears to be related to generics in the compiler frontend (?), CC @griesemer @mdempsky @danscales

@mknyszek mknyszek changed the title [dev.typeparams] implict dereference using constraints doesn't compile as expected cmd/compile: implict dereference using constraints doesn't compile with -G=3 as expected Aug 16, 2021
@mknyszek mknyszek added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Aug 16, 2021
@mknyszek mknyszek added this to the Go1.18 milestone Aug 16, 2021
@abraithwaite
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I'll try it on the master branch too! Thanks for the update.

@griesemer
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This is an error reported by the compiler when writing object data to disk. The compiler front-end (types2, etc.) accepts this code just fine.

@mdempsky
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mdempsky commented Aug 16, 2021 •
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I think this is actually an issue with method wrapper generation with -G=3 mode. The error message is because the generated code is not well typed.

(FWIW, it compiles and runs okay with GOEXPERIMENT=unified.)

@danscales danscales self-assigned this Aug 22, 2021
@danscales
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This relates to some discrepancy in the naming of types, which leads to problems with wrapper generation. I'll have a fix in the next day or so.

@danscales danscales mentioned this issue Aug 23, 2021
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@gopherbot
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Change https://golang.org/cl/344613 mentions this issue: cmd/compile: fix naming of types inside instantiations

@golang golang locked and limited conversation to collaborators Jun 23, 2023
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