govet fieldalignment produces false positives for embedded structures

[iamtakingiteasy]

• 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

govet's fieldalignment produces false positives for embedded structures. maligned has no such issue, running go vet also does not report same thing.

Version of golangci-lint

$ golangci-lint --version
golangci-lint has version 1.38.0 built from 507703b4 on 2021-03-03T13:53:01Z

Config file

$ cat .golangci.yml
run:
  concurrency: 4
  deadline: 5m
  issues-exit-code: 1
  tests: true

output:
  format: colored-line-number
  print-issued-lines: true
  print-linter-name: true

linters-settings:
  govet:
    check-shadowing: true
    enable:
      - fieldalignment

linters:
  enable:
    - govet
  disable-all: true

Go environment

$ go version && go env
go version go1.15.8 linux/amd64
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOENV="/home/user/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/go/pkg/mod"
GOOS="linux"
GOPATH="/home/go"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build360390239=/tmp/go-build -gno-record-gcc-switches"

Verbose output of running

$ golangci-lint cache clean
$ golangci-lint run -v
INFO [config_reader] Config search paths: [./ /tmp/z /tmp / /home/user] 
INFO [config_reader] Used config file .golangci.yml 
INFO [lintersdb] Active 1 linters: [govet]        
INFO [loader] Go packages loading at mode 575 (deps|compiled_files|exports_file|files|imports|name|types_sizes) took 86.458911ms 
INFO [runner/filename_unadjuster] Pre-built 0 adjustments in 81.861µs 
INFO [linters context/goanalysis] analyzers took 1.044009ms with top 10 stages: ctrlflow: 295.127µs, printf: 246.776µs, unmarshal: 125.055µs, fieldalignment: 61.93µs, inspect: 43.601µs, shadow: 25.146µs, framepointer: 22.24µs, buildtag: 19.501µs, unreachable: 17.748µs, unusedresult: 17.265µs 
INFO [runner] Processors filtering stat (out/in): exclude-rules: 1/1, uniq_by_line: 1/1, path_prefixer: 1/1, path_prettifier: 1/1, autogenerated_exclude: 1/1, max_per_file_from_linter: 1/1, severity-rules: 1/1, cgo: 1/1, filename_unadjuster: 1/1, skip_files: 1/1, skip_dirs: 1/1, identifier_marker: 1/1, diff: 1/1, exclude: 1/1, nolint: 1/1, max_same_issues: 1/1, max_from_linter: 1/1, source_code: 1/1, path_shortener: 1/1, sort_results: 1/1 
INFO [runner] processing took 164.092µs with stages: identifier_marker: 46.124µs, nolint: 36.919µs, exclude-rules: 31.245µs, autogenerated_exclude: 13.726µs, source_code: 11.264µs, path_prettifier: 10.725µs, skip_dirs: 5.291µs, uniq_by_line: 1.645µs, cgo: 1.392µs, max_same_issues: 1.387µs, path_shortener: 891ns, max_from_linter: 856ns, filename_unadjuster: 677ns, max_per_file_from_linter: 530ns, diff: 372ns, skip_files: 283ns, severity-rules: 282ns, exclude: 213ns, sort_results: 155ns, path_prefixer: 115ns 
INFO [runner] linters took 58.431317ms with stages: govet: 58.203915ms 
foo.go:12:10: fieldalignment: struct with 24 pointer bytes could be 16 (govet)
type exA struct {
         ^
INFO File cache stats: 1 entries of total size 262B 
INFO Memory: 3 samples, avg is 72.5MB, max is 72.6MB 
INFO Execution took 148.770601ms  

Code example or link to a public repository

package main

import (
	"fmt"
	"unsafe"
)

type some struct {
	F *int32
}

type exA struct {
	S string
	some
}

type exB struct {
	some
	S string
}

func main() {
	a := exA{}
	b := exB{}

	fmt.Println("a", unsafe.Sizeof(a)) // 24
	fmt.Println("b", unsafe.Sizeof(b)) // 24
}

[boring-cyborg]

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

[iamtakingiteasy]

golang/go#44877

[iamtakingiteasy]

As per golang/go#44877 (comment) it seems that "pointer bytes" reports from fieldalignment linter correspond to GC scanning the structure rather than structure size. Latter has messages in form of "struct of size X could be Y", and former are "struct with X pointer bytes could be Y", which was pretty confusing. As suggested in linked comment, maybe it is worth ignoring reports of pointer bytes by default in golangci-lint, maybe add an option to handle this.

[iamtakingiteasy]

The issue seems to be rooted in that maligned used in golangci-lint's go.mod is of pretty old version (as of 2018), while GC pointer scan diagnostic was added there 6 months ago. Naturally, this diagnostic was also introduced to fieldalignment too, but it is a noticable change of behavior when trying to use fieldalignment as drop-in replacement to old maligned version which had no such diagnostic in golangci-lint case.

[ldez]

Thank you @iamtakingiteasy for the details behind the fieldalignment behavior.

We can close the issue now.

[atc0005]

@ldez: Thank you @iamtakingiteasy for the details behind the fieldalignment behavior.

We can close the issue now.

Apologies if this was spelled out, but if users enable the govet fieldalignment linter to replace the maligned linter (for struct size linter warnings), how can they avoid the reports regarding pointer bytes?