x/tools/gopls: prefer dependencies from the go.mod when populating imports

[artyom]

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

$ go version
go version go1.16.2 darwin/arm64

$ gopls version
golang.org/x/tools/gopls v0.6.9
    golang.org/x/tools/gopls@v0.6.9 h1:LBBcE2y3Tb4bp79JVLWCQBbvYCFEs5ADGWsQDoSLk1Q=

Does this issue reproduce with the latest release?

N/a.

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/artyom/Library/Caches/go-build"
GOENV="/Users/artyom/Library/Application Support/go/env"
GOEXE=""
GOFLAGS="-ldflags=-w -trimpath"
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/artyom/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/artyom/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/artyom/Library/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/artyom/Library/go/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.16.2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/tmp/fail/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/lb/3rk8rqs53czgb4v35w_342xc0000gn/T/go-build1158719527=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

1. Create an empty directory, initialize a new module there with go init demo

2. Add dependency: go get github.com/aws/aws-sdk-go-v2/aws

3. Open VS Code with Go extension that relies on gopls v0.6.9, and type the following:

   package main
   
   func main() {
   	_ = aws.String("demo")
   }

4. Save the file, triggering gopls to fill the import section

What did you expect to see?

gopls uses the dependency from the go.mod:

package main

import "github.com/aws/aws-sdk-go-v2/aws"

func main() {
	_ = aws.String("demo")
}

What did you see instead?

gopls incorrectly populated imports with the github.com/aws/aws-sdk-go/aws package.

package main

import "github.com/aws/aws-sdk-go/aws"

func main() {
	_ = aws.String("demo")
}

gopls log from VS Code Problems view

[Info  - 4:04:57 PM] 2021/03/24 16:04:57 go env for /private/tmp/fail
(root /private/tmp/fail)
(go version go version go1.16.2 darwin/arm64)
(valid build configuration = true)
(build flags: [])
GOFLAGS=-ldflags=-w -trimpath
GOMODCACHE=/Users/artyom/go/pkg/mod
GOPATH=/Users/artyom/go
GOPROXY=https://proxy.golang.org,direct
GOROOT=/Users/artyom/Library/go
GONOSUMDB=
GOSUMDB=sum.golang.org
GO111MODULE=on
GOINSECURE=
GONOPROXY=
GOPRIVATE=
GOCACHE=/Users/artyom/Library/Caches/go-build
GOMOD=/private/tmp/fail/go.mod
[Info  - 4:04:58 PM] 2021/03/24 16:04:58 go/packages.Load

snapshot=0

directory=/private/tmp/fail

query=[builtin demo/...]

packages=2
[Error - 4:05:21 PM] Request textDocument/codeAction failed.

Message: context canceled

Code: 0

[Info  - 4:05:23 PM] 2021/03/24 16:05:23 go/packages.Load

snapshot=3

directory=/private/tmp/fail

query=[file=/private/tmp/fail/main.go]

packages=1
[Info  - 4:05:23 PM] 2021/03/24 16:05:23 go/packages.Load

snapshot=3

package="demo"

files=[/private/tmp/fail/main.go]
[Error - 4:05:23 PM] 2021/03/24 16:05:23 demo: no dep handle for github.com/aws/aws-sdk-go/aws: no metadata for github.com/aws/aws-sdk-go/aws

snapshot=3
[Error - 4:05:23 PM] 2021/03/24 16:05:23 diagnosing go.mod: err: exit status 1: stderr: go: finding module for package github.com/aws/aws-sdk-go/aws

demo imports

github.com/aws/aws-sdk-go/aws: cannot find module providing package github.com/aws/aws-sdk-go/aws: module lookup disabled by GOPROXY=off
[Error - 4:05:23 PM] 2021/03/24 16:05:23 demo: no dep handle for github.com/aws/aws-sdk-go/aws: no metadata for github.com/aws/aws-sdk-go/aws

snapshot=4
[Error - 4:05:24 PM] 2021/03/24 16:05:24 diagnosing go.mod: err: exit status 1: stderr: go: finding module for package github.com/aws/aws-sdk-go/aws

demo imports

github.com/aws/aws-sdk-go/aws: cannot find module providing package github.com/aws/aws-sdk-go/aws: module lookup disabled by GOPROXY=off

[stamblerre]

Thank you for this detailed issue report! This is the same as #36077, so I will close it as a duplicate.