go - Packages disabled by build tags still linked into binary

Question

I use build tags to disable one feature, such as:

source

• abc_enable.go

// +build abc
package main

import (
  "big-package"
  "bigbig"
)
...

• abc_disable.go

// +build !abc

// empty

build cmd

• enable: go build --tags abc
• disable: go build

this method works always.

problem

but I found build binary size keeps big when abc disabled.

• keep abc_enable.go, --tags abc. size up to 11M
• keep abc_enable.go, no tags. size up to 11M
• remove abc_enable.go by hand, size down to 5M

is there any link options or build options to fix this?

Answer 1

Build constraints

To distinguish build constraints from package documentation, a series of build constraints must be followed by a blank line.

That means that // +build abc in your original code snippet is not considered a build constraint. To fix this you have to add a blank line above of the package clause.

// +build abc

package main

import (
  "big-package"
  "bigbig"
)
...