go/parser: cannot parse channel of channel with receive direction

[vladimiroff]

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

$ go version
go version go1.17.1 linux/amd64

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/kiril/.cache/go-build"
GOENV="/home/kiril/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.1"
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-build4024821342=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Tried to make channel of channels with receive direction: https://play.golang.org/p/1dR3qhjMF90

Simplified example, where a single click on "Format" highlights the issue: https://play.golang.org/p/M8Yn3NAP6V5
At first I thought this is a bug in gofmt, changing the semantic of my code.

What did you expect to see?

Expected to be able to send channels with receive-only direction through that channel.

What did you see instead?

The "root" channel is made with send-only direction instead, during make, thus making it useless:

./prog.go:9:9: invalid operation: <-chch (receive from send-only type chan<- chan int)

Workaround

Adding parentheses around the inner channel solves the issue:

	chch := make(chan (<-chan int))

[ALTree]

This is working as expected, from the Language specification:

The <- operator associates with the leftmost chan possible:

chan<- chan int // same as chan<- (chan int)

as you noted, you need parentheses to get the direction to be associated to the right channel.