erroneous judgement to "declared but not used"

[dereknex]

Welcome

• Yes, I'm using a binary release within 2 latest major releases. Only such installations are supported.
• Yes, I've searched similar issues on GitHub and didn't find any.
• Yes, I've included all information below (version, config, etc).
• Yes, I've tried with the standalone linter if available. (https://golangci-lint.run/usage/linters/)

Description of the problem

Go code as below:

       // ClusterIPRanges
	_, ipNet, err := net.ParseCIDR(DefaultCIDR)
	if err != nil {
		return errors.Wrapf(err, "invalid cluster-cidr %s", DefaultCIDR)
	}
	cfg.ControlConfig.ClusterIPRanges = append(cfg.ControlConfig.ClusterIPRanges, ipNet)

Got error:

cmd/geda/app/bootstrap/k3s.go:23:5: ipNet declared but not used (typecheck)
	_, ipNet, err := net.ParseCIDR(DefaultCIDR)
	   ^

Version of golangci-lint

$ golangci-lint --version
# golangci-lint has version 1.42.0 built from c6142e3 on 2021-08-17T08:27:57Z

Configuration file

$ cat .golangci.yml
# run:
  concurrency: 4
  deadline: 5m

linter-settings:
  goconst:
    min-len: 2
    min-occurrences: 2

linters:
  enable:
    - goconst
    - gofmt
    - goimports
    - misspell
    - unparam

issues:
  exclude-use-default: false
  exclude-rules:
    - path: _test.go
      linters:
        - errcheck
  exclude:
    - (comment on exported (method|function|type|const)|should have( a package)? comment|comment should be of the form)

Go environment

$ go version && go env
# go version go1.16.6 darwin/amd64
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/derek/Library/Caches/go-build"
GOENV="/Users/derek/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/derek/go/pkg/mod"
GOOS="darwin"
GOPATH="/Users/derek/go"
GOPROXY="https://goproxy.io,direct"
GOROOT="/usr/local/Cellar/go/1.16.6/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.16.6/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16.6"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/derek/Workspaces/geda/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 x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/mf/y5s_1mcx3vb0n7thsn_d_g3c0000gn/T/go-build172231809=/tmp/go-build -gno-record-gcc-switches -fno-common"

Verbose output of running

$ golangci-lint cache clean
$ golangci-lint run -v
#INFO [config_reader] Config search paths: [./ /Users/derek/Workspaces/geda /Users/derek/Workspaces /Users/derek /Users /]
INFO [config_reader] Used config file .golangci.yml
INFO [lintersdb] Active 15 linters: [deadcode errcheck goconst gofmt goimports gosimple govet ineffassign misspell staticcheck structcheck typecheck unparam unused varcheck]
INFO [loader] Go packages loading at mode 575 (compiled_files|deps|name|types_sizes|exports_file|files|imports) took 4.077825318s
INFO [runner/filename_unadjuster] Pre-built 0 adjustments in 1.571762ms
INFO [linters context/goanalysis] analyzers took 6m5.377470535s with top 10 stages: buildir: 5m8.273972594s, nilness: 27.449475311s, inspect: 5.80335826s, ctrlflow: 4.623810022s, typedness: 4.563202093s, fact_deprecated: 4.488277725s, printf: 3.933454729s, fact_purity: 3.54004935s, SA5012: 2.428113135s, buildssa: 74.200227ms
INFO [runner] Issues before processing: 153, after processing: 1
INFO [runner] Processors filtering stat (out/in): uniq_by_line: 1/144, max_same_issues: 1/1, skip_dirs: 153/153, exclude: 153/153, exclude-rules: 153/153, identifier_marker: 153/153, skip_files: 153/153, autogenerated_exclude: 153/153, nolint: 144/153, path_prefixer: 1/1, sort_results: 1/1, filename_unadjuster: 153/153, path_prettifier: 153/153, diff: 1/1, max_per_file_from_linter: 1/1, max_from_linter: 1/1, source_code: 1/1, path_shortener: 1/1, severity-rules: 1/1, cgo: 153/153
INFO [runner] processing took 5.576239ms with stages: nolint: 2.109345ms, identifier_marker: 1.822508ms, autogenerated_exclude: 594.325µs, exclude: 565.598µs, path_prettifier: 237.926µs, skip_dirs: 75.92µs, source_code: 71.972µs, exclude-rules: 49.501µs, uniq_by_line: 17.229µs, cgo: 13.296µs, filename_unadjuster: 9.153µs, max_same_issues: 3.138µs, path_shortener: 1.692µs, max_per_file_from_linter: 1.33µs, max_from_linter: 1.206µs, diff: 762ns, skip_files: 494ns, severity-rules: 376ns, sort_results: 303ns, path_prefixer: 165ns
INFO [runner] linters took 1m46.354873834s with stages: goanalysis_metalinter: 1m46.349154728s
cmd/geda/app/bootstrap/k3s.go:23:5: ipNet declared but not used (typecheck)
        _, ipNet, err := net.ParseCIDR(DefaultCIDR)
           ^
INFO File cache stats: 6 entries of total size 21.6KiB
INFO Memory: 707 samples, avg is 2054.8MB, max is 3045.6MB
INFO Execution took 1m50.449564677s

Code example or link to a public repository

      // ClusterIPRanges
	_, ipNet, err := net.ParseCIDR(DefaultCIDR)
	if err != nil {
		return errors.Wrapf(err, "invalid cluster-cidr %s", DefaultCIDR)
	}
	cfg.ControlConfig.ClusterIPRanges = append(cfg.ControlConfig.ClusterIPRanges, ipNet)

[boring-cyborg[bot]]

Hey, thank you for opening your first Issue ! 🙂 If you would like to contribute we have a guide for contributors.

[ldez]

Hello,

Can you provide a full reproducible example?

typecheck can not make "errors of judgment", because typecheck is not a linter but a way to catch compilation error in your code.

[dereknex]

@ldez I try to write a simple example. It isn't able to reproduce.

package main

import (
	"fmt"
	"net"
)

func main() {
	ipNets := []*net.IPNet{}
	_, ipNet, err := net.ParseCIDR("10.42.0.0/16")
	if err != nil {
		panic(err)
	}
	ipNets = append(ipNets, ipNet)
	fmt.Printf("%v\n", ipNets)
}

The source code of the problem is here https://github.com/dereknex/geda/blob/provision-nodes/cmd/geda/app/bootstrap/k3s.go . I will try again.

[anxinyf]

I have a try to the example, it's ok!

But there's a same issue in my code!
error:

...
2021-08-30 16:48:52.000 level=info msg="[runner] linters took 33.418162965s with stages: goanalysis_metalinter: 33.407029009s"
2021-08-30 16:48:52.000 manager.go:220:3: mac declared but not used (typecheck)
2021-08-30 16:48:52.000 		mac, err := getDefaultGatewayMac()
2021-08-30 16:48:52.000 		^
2021-08-30 16:48:52.000 level=info msg="File cache stats: 81 entries of total size 275.3KiB"
2021-08-30 16:48:52.000 level=info msg="Memory: 686 samples, avg is 637.4MB, max is 1708.3MB"
2021-08-30 16:48:52.000 level=info msg="Execution took 1m11.907422275s"

function like:

var GatewayMac [6]byte
func ReSync() error {
  mac, err := getDefaultGatewayMac()
  if err != nil {
    return fmt.Errorf("failed to get default gateway: %v", err)
  }
  copy(GatewayMac[:], mac)

  return nil
}

mac is in use obviously！

.golangci.yml

linters:
  enable:
    - deadcode
    - dupl
    - errcheck
    - goconst
    - gocyclo
    - gofmt
    #- golint #no longer supported
    #- goimports
    #- gosec
    - gosimple
    - govet
    - ineffassign
    #- interfacer #no longer supported
    - lll
    #- maligned #no longer supported
    - misspell
    - nakedret
    - prealloc
    #- scopelint #no longer supported
    - staticcheck
    - structcheck
    - typecheck
    - unconvert
    - unparam
    - unused
    - varcheck
    - bodyclose
    # - exhaustive
    # - exhaustivestruct
    - exportloopref
    - goprintffuncname
    # - forcetypeassert

linters-settings:
  errcheck:
    # path to a file containing a list of functions to exclude from checking
    # see https://github.com/kisielk/errcheck#excluding-functions for details
    exclude: .errcheck_exclude.txt

issues:
  exclude-rules:
    - linters:
        - unparam
      source: "getList\\).remove"

run:
  skip-dirs:
    - pkg
  skip-files:
    - ".*test.go$"
  skip-dirs-use-default: true

command:
golangci-lint run -c .golangci.yml --allow-parallel-runners -v --timeout 10m

go version
go version go1.15 linux/amd64

golangci-lint --version
golangci-lint has version 1.41.1 built from a2074809 on 2021-06-19T16:01:50Z

[anxinyf]

After I changed the golang version 1.15 to version 1.16, it's OK in my code!
But don't know why.

[bensaufley]

I'm encountering this in a simple loop statement. My Go version is 1.17. Unfortunately can't share as it's a private repo but it's a very simple piece of code:

collection := make([]Thing, len(listOfThings))
for i, thing := range listOfThings {
  collection[i] = actOn(thing)
}

typecheck says i declared but not used; GoLand does not show i as unused, and of course, it's obviously not unused.

Actually noticing a lot of this. Imported packages marked as not used, but they're used…

I'm just starting to add golangci-lint to a new (successfully-compiling) project so there's a lot of failures. Most of them are style/optimization and they're correct, but typecheck is just … wrong.

[ldez]

typecheck cannot be wrong because it's just a way to display "compilation" errors. It's just an error catcher around the Go standard tooling.

You have to check your project and maybe run go mod tidy.

[bensaufley]

I've seen the argument above that it "cannot be wrong" but obviously it is wrong. i is obviously used. The question is why does it think it isn't, and why do other tools know better?

On further investigation it looks like completely unrelated issues, including missing imports somewhere in the project or at least the package, can cause this. Still curious what causes the false positives there though.

[konart]

I have the same problem with jaeger import. I can build and run golangci (or go vet, or any other command for that matter) just fine, but as soon as the golangci-lint is executed inside docker I get typecheck error:

"github.com/uber/jaeger-client-go" imported but not used as jaeger (typecheck)
	"github.com/uber/jaeger-client-go"

```go
package middleware

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"net/http"

	"github.com/go-chi/chi/v5/middleware"
	"github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/ext"
	"github.com/uber/jaeger-client-go"

	"gitlab.goodsteam.tech/goods/merchants-experience/MMS/infrastructure/tracing"
	t "gitlab.goodsteam.tech/goods/merchants-experience/MMS/mms-hub/internal/infrastructure/tracer"
)

jaegerSpanContext, ok := span.Context().(jaeger.SpanContext)
if ok {
    ctx = context.WithValue(ctx, keyTraceID, jaegerSpanContext.TraceID().String())
} else {
   ctx = context.WithValue(ctx, keyTraceID, NoJaeger)
}

The next stage in the pipeline (go build basically) executes without an issue though (if lining stage is ommited).

I did go mod tidy and go mod verify and even rerun go get for this package just to make sure, lol.

[konart]

❯ go version
go version go1.17.1 darwin/amd64
❯ golangci-lint version
golangci-lint has version 1.42.1 built from 54f4301 on 2021-09-04T14:39:09Z

[konart]

Figured this out.
I'm not sure how exactly this works but the problem was not with jaeger or its usage. We have a number of dependencies from our private repo. To get and use them you need a .netrc hack with your gitlab token info, otherwise go mod and similar commands will fail. And if they fail golangci-lint fails too except even in verbose mode it says nothing about lack of deps.

[sirn]

This fixed the problem for us as well. We started having "imported but not used" issue since we introduced dependencies in private repository. Our runner doesn't have access to those repositories during lint (but does during build) and caused this issue. We modified our build script to grant access to the repository during lint and it now runs without any "imported but not used" issue.