Tool to detect Go structs that would take less memory if their fields were sorted.

Since c37866e2d38b8e33600b215e4095af870becd4d8, maligned complains on duplicate methods in different custom build tags.

main.go

package main

func main() {
	debug("x")
}

debug.go

// +build debug

package main

func debug(s string) { println(s) }

release.go

// +build !debug

package main

func debug(string) {}

 % maligned *.go
/tmp/release.go:5:6: debug redeclared in this block
/tmp/debug.go:5:6:      other declaration of debug
/tmp/release.go:5:6: debug redeclared in this block
/tmp/debug.go:5:6:      other declaration of debug
maligned: 4 errors during loading

Before c37866e2d38b8e33600b215e4095af870becd4d8, maligned worked well in this situation.

This seems much simpler and more reliable than hard-coding the sizes. Additionally, it seems strange that types.Int and types.Uint weren't originally included in the basicSizes map. Maybe they were defined as aliases of size-specific types when maligned was written but have since been redefined as unique types?

For complex structs, it's almost impossible to find the correct combination without knowing the fine details of the alignment rules.

If it was easy, this whole tool would not be needed at all.

When scanning objects during GC, the standard compiler/runtime only scan as far as the last pointer slot in an object. If fields are sorted so that all of the pointer-y fields come first, then the GC may be able to short-circuit its scan work slightly.

I got this compilation error while executing go get github.com/mdempsky/maligned with Go1.5.1:

./maligned.go:50: impossible type assertion: *"golang.org/x/tools/go/types".Struct does not implement "go/types".Type (wrong type for Underlying method) have Underlying() "golang.org/x/tools/go/types".Type want Underlying() "go/types".Type

github.com/golang/tools introduced an API change for go/types around commit: https://github.com/golang/tools/commit/2477c0d5780ddec6439a9322a6862dfe20cc8b81.

As pointed out on Twitter. This would add support for modules, and also modernize the tool quite a bit as go/loader hasn't been supported in years.

When done, please update https://github.com/golang/go/issues/24661 with a comment so that the "maligned" checklist item can be ticked off.

Support import path patterns, including within relative import paths. When given 0 arguments, use the package in current working directory. If the import path patterns match no packages, print a warning and exit with 0 exit code.

Rely on go/loader to resolve relative import paths relative to current working directory.

Fixes #4.

Similar to mdempsky/unconvert#9.

Hi,

I am wondering if I can explicitly skip running maligned check on any given struct rather than globally checking either all or none?

Regards

This is how I wish to return JSON response

{
   "id": 1,
   "name": "hello",
   "is_active": true,
   "created_at": "2019-01-01"
}

struct{
	ID       	uint16
	Name     	string
	IsActive 	bool
	CreatedAt	string
}

However, it is not possible because struct is not maligned and I have to malign it and the response looks odd.

struct{
	Name     	string
	CreatedAt	string
	ID       	uint16
	IsActive 	bool
}

{
   "name": "hello",
   "created_at": "2019-01-01",
   "id": 1,
   "is_active": true
}

Some annotation solution like this, maybe!

// @skip: maligned
struct{
	ID       	uint16
	Name     	string
	IsActive 	bool
	CreatedAt	string
}

👋🏽 hi

What

awesome tool! I see it is deprecated, so I think it's best to archive the repo, which will keep it public, but warn the users that it is no longer maintained 🙂

hi, i know that fieldalignment now preferred way to check/fix field alignment in golang structs. how to deal with it if i want to have automatic align fields via own golang program? (for example i'm generate code from protobuf)

Add -v to display fields where padding is added.

Example:

...\encoder_options.go:14:21: struct of size 64 could be 56
Field sizes in order:
        *  concurrent int: 8:8
        *  crc bool: 1:1
        !!!  single *bool: 8:15
        *  pad int: 8:8
        *  blockSize int: 8:8
        *  windowSize int: 8:8
        *  level github.com/klauspost/compress/zstd.EncoderLevel: 8:8
        *  fullZero bool: 1:1
        *  noEntropy bool: 1:1

This is a great project. Thank you for sharing it with the community.

I discovered the project when gometalinter ran against some of my code and found an inefficient alignment in one of my code's structs. But when I looked up the project, I found nothing in the README or the GoDoc that explained why memory alignment is a good thing or how I might achieve it.

I read Padding is hard which helped, but wonder if we might add something in the README or even the source code to help others who might have the same problem.

/cc @markmandel

Given the code:

model.go

package addrs

// ASDExchanger bla bla
type ASDExchanger struct {
	ASDBtcExchangeRate    string `mapstructure:"asd_btc_exchange_rate"`
	ASDBtcExchangeRateUSD string `mapstructure:"asd_btc_exchange_rate_usd"`
	ASDBtcExchangeLabel   string `mapstructure:"asd_btc_exchange_label"`
	ASDBtcExchangeEnabled bool   `mapstructure:"asd_btc_exchange_enabled"`

	ASDEthExchangeRate    string `mapstructure:"asd_eth_exchange_rate"`
	ASDEthExchangeRateUSD string `mapstructure:"asd_eth_exchange_rate_usd"`
	ASDEthExchangeLabel   string `mapstructure:"asd_eth_exchange_label"`
	ASDEthExchangeEnabled bool   `mapstructure:"asd_eth_exchange_enabled"`

	ASDSkyExchangeRate    string `mapstructure:"asd_sky_exchange_rate"`
	ASDSkyExchangeRateUSD string `mapstructure:"asd_sky_exchange_rate_usd"`
	ASDSkyExchangeLabel   string `mapstructure:"asd_sky_exchange_label"`
	ASDSkyExchangeEnabled bool   `mapstructure:"asd_sky_exchange_enabled"`

	ASDWavesExchangeRate    string `mapstructure:"asd_waves_exchange_rate"`
	ASDWavesExchangeRateUSD string `mapstructure:"asd_waves_exchange_rate_usd"`
	ASDWavesExchangeLabel   string `mapstructure:"asd_waves_exchange_label"`
	ASDWavesExchangeEnabled bool   `mapstructure:"asd_waves_exchange_enabled"`

	ASDWavesASDExchangeRate    string `mapstructure:"asd_waves_asd_exchange_rate"`
	ASDWavesASDExchangeRateUSD string `mapstructure:"asd_waves_asd_exchange_rate_usd"`
	ASDWavesASDExchangeLabel   string `mapstructure:"asd_waves_asd_exchange_label"`
	ASDWavesASDExchangeEnabled bool   `mapstructure:"asd_waves_asd_exchange_enabled"`
}

When I run gometalinter and maligned:

gometalinter --deadline=3m -j 2 --disable-all --tests --vendor \                                                                                             
        -E maligned \       
        ./...

Then throws me err:

model.go:4:19:warning: struct of size 280 could be 248 (maligned)

When I remove the bool and or replace with string, it works with no errs.

Any ideas ?