golang/go

x/tools/gopls: reverse type inference for completions in generic function call params

jacobzim-stl opened this issue · 2 comments

jacobzim-stl commented

gopls version

golang.org/x/tools/gopls v0.0.0-20240919171440-cd349f34d533+dirty
golang.org/x/tools/gopls@v0.0.0-20240919171440-cd349f34d533+dirty
github.com/BurntSushi/toml@v1.2.1 h1:9F2/+DoOYIOksmaJFPw1tGFy1eDnIJXg+UHjuD8lTak=
github.com/google/go-cmp@v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
golang.org/x/exp/typeparams@v0.0.0-20221212164502-fae10dda9338 h1:2O2DON6y3XMJiQRAS1UWU+54aec2uopH3x7MAiqGW6Y=
golang.org/x/mod@v0.21.0 h1:vvrHzRwRfVKSiLrG+d4FMl/Qi4ukBCE6kZlTUkDYRT0=
golang.org/x/sync@v0.8.0 h1:3NFvSEYkUoMifnESzZl15y791HH1qU2xm6eCJU5ZPXQ=
golang.org/x/telemetry@v0.0.0-20240829154258-f29ab539cc98 h1:Wm3cG5X6sZ0RSVRc/H1/sciC4AT6HAKgLCSH2lbpR/c=
golang.org/x/text@v0.18.0 h1:XvMDiNzPAl0jr17s6W9lcaIhGUfUORdGCNsuLmPG224=
golang.org/x/tools@v0.21.1-0.20240508182429-e35e4ccd0d2d => ../
golang.org/x/vuln@v1.0.4 h1:SP0mPeg2PmGCu03V+61EcQiOjmpri2XijexKdzv8Z1I=
honnef.co/go/tools@v0.4.7 h1:9MDAWxMoSnB6QoSqiVr7P5mtkT9pOc1kSxchzPCnqJs=
mvdan.cc/gofumpt@v0.7.0 h1:bg91ttqXmi9y2xawvkuMXyvAA/1ZGJqYAEGjXuP0JXU=
mvdan.cc/xurls/v2@v2.5.0 h1:lyBNOm8Wo71UknhUs4QTFUNNMyxy2JEIaKKo0RWOh+8=
go: devel go1.24-097b7162ad Fri Sep 20 20:19:15 2024 +0000

go env

GO111MODULE=''
GOARCH='arm64'
GOBIN='/Users/jzimmerman-stainless/go/bin'
GOCACHE='/Users/jzimmerman-stainless/Library/Caches/go-build'
GOENV='/Users/jzimmerman-stainless/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/jzimmerman-stainless/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/jzimmerman-stainless/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/jzimmerman-stainless/Desktop/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/jzimmerman-stainless/Desktop/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='devel go1.24-097b7162ad Fri Sep 20 20:19:15 2024 +0000'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/jzimmerman-stainless/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/dd/02btngf95192vx03n6g2t8gh0000gn/T/go-build3842107580=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

This is a feature request.

When writing a generic function that returns a parameterized type in an assignment, gopls makes no "reverse type inferences" for completions in the function parameters. With reverse type inference, completions could exist for type parameters, and automatic conversion completions for interface types.

I have a video that demonstrates a patched implementation with this working

completions.mov

I measured that when using libraries that make heavy use of generics, there is a roughly 5x productivity boost after this was patched.

What did you see happen?

type Wrap[T any] struct {
      inner: *T	
}

func NewWrap[T any](x T) {
     return Wrap[T]{ inner: &x }
}

type InterfaceA interface {
        implA()
}

type TypeA struct {}

func (t TypeA) implA() {}

func main() {
	var ta TypeA
	var ia InterfaceA
	
	var w Wrap[InterfaceA]
    w = NewWrap(/* cursor here */)     // case 1
    w = NewWrap[/* cursor here */]()  // case 2
}

No special completions, just lexical

What did you expect to see?

Case 1.
I would expect completions of with the following options
ia
ta
TypeA{}

Additionally, ta and TypeA{} should have a conversion to InterfaceA(ta) or InterfaceA(TypeA{}) when they are selected.

Case 2.
This should complete to the type name InterfaceA

Editor and settings

No response

Logs

No response

gopherbot commented

Change https://go.dev/cl/618675 mentions this issue: completions/inference: infer polymorphic types in completions