Golangci-lint: False positive for structcheck linter

[lukasmalkmus]

Thank you for creating the issue!

• [x] Yes, I'm using a binary release within 2 latest major releases. Only such installations are supported.
• [x] Yes, I've searched similar issues on GitHub and didn't find any.
• [x] Yes, I've included all information below (version, config, etc).

Please include the following information:

Version of golangci-lint

$ golangci-lint --version
golangci-lint has version 1.32.2 built from 52d26a3 on 2020-11-03T01:15:38Z

Config file

$ cat .golangci.yml
linters:
  disable-all: true
  enable:
    - structcheck

Go environment

$ go version && go env
go version go1.15.5 darwin/amd64
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/lukasmalkmus/Library/Caches/go-build"
GOENV="/Users/lukasmalkmus/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/lukasmalkmus/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/lukasmalkmus/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/opt/[email protected]/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/opt/[email protected]/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/dy/s6dd70892l35f0444cwt96t40000gn/T/go-build258997589=/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/lukasmalkmus/Code/OSS/golangci-lint-unused-issue /Users/lukasmalkmus/Code/OSS /Users/lukasmalkmus/Code /Users/lukasmalkmus /Users /] 
INFO [config_reader] Used config file .golangci.yml 
INFO [lintersdb] Active 1 linters: [structcheck]  
INFO [loader] Go packages loading at mode 575 (types_sizes|deps|imports|name|compiled_files|exports_file|files) took 58.89566ms 
INFO [runner/filename_unadjuster] Pre-built 0 adjustments in 1.306913ms 
INFO [linters context/goanalysis] analyzers took 411.503µs with top 10 stages: structcheck: 411.503µs 
INFO [runner] Processors filtering stat (out/in): exclude-rules: 1/1, max_per_file_from_linter: 1/1, skip_dirs: 1/1, identifier_marker: 1/1, sort_results: 1/1, nolint: 1/1, diff: 1/1, max_same_issues: 1/1, max_from_linter: 1/1, source_code: 1/1, path_prefixer: 1/1, cgo: 1/1, filename_unadjuster: 1/1, autogenerated_exclude: 1/1, exclude: 1/1, uniq_by_line: 1/1, path_shortener: 1/1, severity-rules: 1/1, path_prettifier: 1/1, skip_files: 1/1 
INFO [runner] processing took 1.266122ms with stages: autogenerated_exclude: 847.753µs, exclude: 106.116µs, path_prettifier: 87.223µs, nolint: 86.367µs, source_code: 57.543µs, identifier_marker: 30.058µs, skip_dirs: 26.597µs, filename_unadjuster: 7.692µs, uniq_by_line: 3.782µs, max_same_issues: 3.429µs, cgo: 2.592µs, path_shortener: 1.914µs, max_from_linter: 1.446µs, max_per_file_from_linter: 796ns, diff: 559ns, exclude-rules: 553ns, skip_files: 546ns, severity-rules: 409ns, sort_results: 385ns, path_prefixer: 362ns 
INFO [runner] linters took 491.719474ms with stages: structcheck: 490.285749ms 
test.go:4:2: `b` is unused (structcheck)
        b string
        ^
INFO File cache stats: 1 entries of total size 102B 
INFO Memory: 7 samples, avg is 71.8MB, max is 71.8MB 
INFO Execution took 598.573223ms

package issue

type a struct {
    b string
}

type A a

var b = A{"b"}

func B() string {
    return b.b
}

Thies yields an error which isn't true:

test.go:4:2: `b` is unused (structcheck)
        b string
        ^

Field b is used.

[rafaelkperes]

There's an open old issue for the linter: https://gitlab.com/opennota/check/-/issues/11.

As stated in their docs:

Known limitations

structcheck doesn't handle embedded structs yet.

[iwankgb]

@lukasmalkmus, it will take a while I think. Before I fix it I will try to get rid of the fork and move golangci-lint to upstream version. I will keep updating this issue.

[iwankgb]

@lukasmalkmus unfortunately it does not seem to be possible to switch golangci-lint to upstream structcheck. There are too fundamental differences between the fork: we use golang.org/x/tools/go/analysis and structcheck upstream uses golang.org/x/tools/go/packages. Whole point of the for has been to rewrite whole check repo, apparently. There are no tests there so the refactoring/rewrite looks risky to me.
Merging changes from the upstream to the fork seems to be equally complicated and it looks like we have separate project to maintain nowadays. I'm not sure if this is something that we are ready to invest into. @golangci/team, @ernado - what do you think?

[iwankgb]

@golangci/team do we want to invest time in maintaining forks in golangci organization?

[SVilgelm]

@iwankgb IMO we need to get rid of as much as possible forks and use the original projects.