cmd/compile: internal compiler error: found illegal assignment on test example

[esimov]

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

$ go version
go version go1.18.5 linux/amd64

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/esimo/.cache/go-build"
GOENV="/home/esimo/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/esimo/projects/Go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/esimo/projects/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="go1.18.5"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/esimo/projects/Go/src/esimov/torx/go.mod"
GOWORK="/home/esimo/projects/Go/src/esimov/go.work"
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-build1479111117=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I was experimenting with generics and implemented a service retry utility function which looks like the following (some irrelevant part might be skipped):

func TestFunc_RetryWithDelay(t *testing.T) {
	rand.Seed(time.Now().UTC().UnixNano())

	assert := assert.New(t)

	n := 5
	idx := 0
	ForEach([]int{1, 2, 3, 4, 5, 6, 7}, func(val int) {
		rt := RType[int]{Input: val}
		d, att, e := rt.RetryWithDelay(n, 20*time.Millisecond, func(d time.Duration, elem int) (err error) {
			if elem%2 != 0 {
				err = fmt.Errorf("retry failed: number of %d attempts exceeded", n)
			}
			return err
		})
		switch idx {
		case 0, 2:
			assert.GreaterOrEqual(int(d.Milliseconds()), 100)
			assert.Equal(5, att)
			assert.Error(e)
		case 1, 3:
			assert.LessOrEqual(int(d.Milliseconds()), 10)
			assert.Equal(0, att)
			assert.NoError(e)
		}
		idx++
	})

	// In this example we are simulating an external service. In case the response time
	// exceeds a certain time limit we stop retrying and an error is returned.
	services := []struct {
		service string
		time    time.Duration
	}{
		{service: "AWS1"},
		{service: "AWS2"},
	}

	type Service[T ~string] struct {
		Service T
		Time    time.Duration
	}

	for _, srv := range services {
		r := random(1, 10)

		// Here we are simulating the response time of the external service
		// by generating some random duration between 1ms and 10ms.
		// All the test should pass because all of the responses are inside the predefined limit (10ms).
		service := Service[string]{
			Service: srv.service,
			Time:    time.Duration(r) * time.Millisecond,
		}
		rtyp := RType[Service[string]]{
			Input: service,
		}

		d, att, e := rtyp.RetryWithDelay(n, 20*time.Millisecond, func(d time.Duration, srv Service[string]) (err error) {
			if srv.Time.Milliseconds() > 10 {
				err = fmt.Errorf("retry failed: service time exceeded")
			}
			return err
		})
		assert.NoError(e)
		assert.Equal(0, att)
		assert.LessOrEqual(int(d.Milliseconds()), 10)
	}

	for _, srv := range services {
		r := random(20, 30)

		// Here we are simulating the response time of the external service
		// by generating some random duration between 20ms and 30ms.
		// All the test should fail because all of the responses are outside the predefined limit (10ms).
		service := Service[string]{
			Service: srv.service,
			Time:    time.Duration(r) * time.Millisecond,
		}
		rtyp := RType[Service[string]]{
			Input: service,
		}

		d, att, e := rtyp.RetryWithDelay(n, 20*time.Millisecond, func(d time.Duration, srv Service[string]) (err error) {
			if srv.Time.Milliseconds() > 10 {
				err = fmt.Errorf("retry failed: service time exceeded")
			}
			return err
		})
		assert.Error(e)
		assert.Equal(5, att)
		assert.Greater(int(d.Milliseconds()), 10)
	}
}

This is working correctly, without producing any kind of issues, but if I'm trying to replicate the same test function as an example, I'm getting the following error:

internal compiler error: found illegal assignment torx.Service[string] -> torx.Service[string];
Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

func Example_FuncRetryWithDelay() {
	n := 5

	// Here we are simulating an external service. In case the response time
	// exceeds a certain limit we stop retrying and we are returning an error.
	services := []struct {
		service string
		time    time.Duration
	}{
		{service: "AWS1"},
		{service: "AWS2"},
	}

	type Service[T ~string] struct {
		Service T
		Time    time.Duration
	}

	for _, srv := range services {
		r := random(1, 10)
		// Here we are simulating the response time of the external service
		// by generating some random duration between 1ms and 10ms.
		// All the test should pass because all of the responses are inside the predefined limit (10ms).
		service := Service[string]{
			Service: srv.service,
			Time:    time.Duration(r) * time.Millisecond,
		}
		rtyp := RType[Service[string]]{
			Input: service, // -------> this is causing the above error.
		}

		d, att, e := rtyp.RetryWithDelay(n, 20*time.Millisecond, func(d time.Duration, srv Service[string]) (err error) {
			if srv.Time.Milliseconds() > 10 {
				err = fmt.Errorf("retry failed: service time exceeded")
			}
			return err
		})
		fmt.Println(e)
		fmt.Println(att)
		fmt.Println(d.Milliseconds())
	}

	// Output:
	// 
}

What did you expect to see?

To run without any kind of errors.

What did you see instead?

The error I mentioned above.

[andig]

Does this reproduce on 1.19?

[esimov]

Yes, it's still reproducing with Go 1.19.3.

$ go version
go version go1.19.3 linux/amd64

[seankhliao]

does it reproduce with tip and can you provide a self contained reproducer?

[esimov]

Here is the self contained reproducer: https://go.dev/play/p/fKiLojMe4D5. Interestingly enough it does not reproduce here. But I have tried on two different instances: go1.19.3 running under Windows WSL and another one go1.18.5 and it does reproduce on both instances.

[randall77]

I cannot get this to reproduce on either 1.18.5 or 1.19.3 (or tip).
I ran with

go test -v issue56916_test.go

where issue56916_test.go contains the exact text of your self-contained reproducer.

Could you be more specific about exactly the commands you used to reproduce? Possibly this has something to do with WSL - could you try on a native linux box?

[mdempsky]

The error message in question ("found illegal assignment") comes from noder/transform.go, which is only used by the non-unified frontend, so this might be fixed in Go 1.20. Though it's also possible we'll just report a different diagnostic instead.

[mdempsky]

Here's a repro: https://go.dev/play/p/LMhy3PPut-C

The issue is that the 1.18/1.19 Go compiler frontend doesn't handle local generic types correctly. This will be fixed in 1.20.

[mdempsky]

Duplicate of #54456.

[esimov]

@mdempsky thanks a lot for checking this up.