cmd/compile: dictionary for [...] should only use concrete types

[pepjo]

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

$ go version
go version go1.18 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/peprf/.cache/go-build"
GOENV="/home/peprf/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/peprf/go/pkg/mod"
GONOPROXY="git.o-c.space*"
GONOSUMDB="git.o-c.space*"
GOOS="linux"
GOPATH="/home/peprf/go"
GOPRIVATE="git.o-c.space*"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/peprf/sdk/go1.18"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/peprf/sdk/go1.18/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.18"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/peprf/projects/satellite-gateway-service/go.mod"
GOWORK=""
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-build2035439223=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I used a complicated mess of generics, interfaces, and maps. Then, tried to run a unit test with the --race flag.

I've only managed to reproduce this using 2 different packages.

• file at /[your project]/pkg/application/bug/bug_test.go

  package bug
  
  import (
      "testing"
  
      "[your project]/pkg/application/other"
  )
  
  type Provider interface {
      Run(other.FetcherByName[other.Something]) ([]byte, error)
  }
  
  func TestNothing(t *testing.T) {}

• file at /[your project]/pkg/application/other/entities.go

  package other
  
  import "fmt"
  
  type Fetcher[thingType Something] struct {
      Thing thingType
  }
  
  func (a Fetcher[thingType]) Get() thingType {
      return a.Thing
  }
  
  type Something interface {
      Name() string
  }
  
  type FetcherByName[thingType Something] map[string]Fetcher[thingType]
  
  func (tp FetcherByName[thingType]) GetFetcherOfThing(t thingType) {
      fetcher := tp[t.Name()]
      fmt.Printf("The fetcher %v for things %s", fetcher, t.Name())
  }

With these files, run:

go test --race ./pkg/application/bug --short

What did you expect to see?

The same that I see without the --race flag:

ok      [your project]/pkg/application/bug     0.001s

What did you see instead?

the output of go test --race ./pkg/application/bug --short is:

# [your project]/pkg/application/bug [[your project]/pkg/application/bug.test]
<autogenerated>:1: internal compiler error: dictionary for Fetcher[go.shape.interface { Name() string }_0].Get should only use concrete types: go.shape.interface { Name() string }_0

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new
FAIL    [your project]/pkg/application/bug [build failed]
FAIL

[ianlancetaylor]

CC @randall77 @mdempsky

[ThinkChaos]

Ran into this with go1.18.1 linux/amd64. Workaround is simple: retry, unfortunately for fixing this, it doesn't seem to occur often.

[pepjo]

At least in 1.18.0, retrying does not seem to solve the issue. We had to add an exception rule in our CI to allow the test to fail. Since I posted this, it has run hundreds of times and it has never worked.