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x/tools/gopls: field alignment warning has issues on custom types #47055

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Karitham opened this issue Jul 5, 2021 · 3 comments
Open

x/tools/gopls: field alignment warning has issues on custom types #47055

Karitham opened this issue Jul 5, 2021 · 3 comments

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@Karitham
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@Karitham Karitham commented Jul 5, 2021

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

❯ go version
go version go1.16.5 linux/amd64
❯ gopls version
golang.org/x/tools/gopls v0.7.0
    golang.org/x/tools/gopls@v0.7.0 h1:JQBHW81Gsyim6iDjUwGoPeSpXrSqwen3isPJLfDfaYU=

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

go env Output
❯ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/karitham/.cache/go-build"
GOENV="/home/karitham/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/karitham/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/karitham/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.5"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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-build3891545200=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Have a struct with a custom type, for example

// session/permission.go
type Permission int64

// ./session.go
type User struct {
	DeletedAt  sql.NullTime       `json:"deleted_at"`
	Email      string             `json:"email"`
	Name       string             `json:"name"`
	Password   string             `json:"password"`
	Permission session.Permission `json:"permission"`
	ID         int32              `json:"id"`
}

What did you see?

struct of size 72 could be 64

What did you expect to see instead?

No warning, since that same exact struct passes with https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/fieldalignment.

The warning also disappears if I replace my custom type with

type User struct {
	DeletedAt  sql.NullTime `json:"deleted_at"`
	Email      string       `json:"email"`
	Name       string       `json:"name"`
	Password   string       `json:"password"`
	Permission int64        `json:"permission"`
	ID         int32        `json:"id"`
}

From my understanding, this issue only applied to types outside the standard library, since I get the issue on all the structs that contains custom types, either mines or from imported packages, such as https://github.com/shopspring/decimal's decimal.Decimal

@mknyszek mknyszek changed the title GOPLS: field alignment warning has issues on custom types x/tools/gopls: field alignment warning has issues on custom types Jul 7, 2021
@gopherbot gopherbot added this to the Unreleased milestone Jul 7, 2021
@mknyszek
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@mknyszek mknyszek commented Jul 7, 2021

CC @stamblerre via https://dev.golang.org/owners

Taking a quick stab at this: it looks like the analysis is assuming you're on a 32-bit platform, which is somewhat surprising to me. On a 64-bit platform that struct is 96 bytes (see https://play.golang.org/p/gbSmYJ9-2XW).

What's even weirder is if on linux/amd64 I run the above program as GOARCH=386 I get 60, which isn't either of the numbers the message is giving you.

@mknyszek
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@mknyszek mknyszek commented Jul 7, 2021

BTW if I add back in the Permission type instead of a raw int64, I get the same numbers.

@findleyr
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@findleyr findleyr commented Jul 7, 2021

This is almost certainly due to AST trimming of packages outside of the workspace: time.Time is effectively a struct{} in the definition of sql.NullTime. This analyzer unfortunately doesn't make any sense in the presence of non-workspace types.

We need a general solution for this, or should consider walking back the AST memory optimizations.

@findleyr findleyr removed this from the Unreleased milestone Jul 7, 2021
@findleyr findleyr added this to the gopls/v1.0.0 milestone Jul 7, 2021
@stamblerre stamblerre added this to To Do in gopls on-deck Jul 15, 2021
@stamblerre stamblerre moved this from To Do to P2 in gopls on-deck Aug 12, 2021
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