Check correctness of import groups in Go source, and fix files that have bad grouping.

Each project should choose a canonical import grouping. For example:

• First standard imports
• Then imports starting with "local/"
• Finally third party imports.

Groups should be separated by empty lines, and within each group imports should be sorted.

So this is allowed:

// In a.go
import (
	"os"
	"testing"
	
	"local/bar"
	"local/foo"
	
	"github.com/Sirupsen/logrus"
	"golang.org/x/net/context"
)

But this is not, because of an extra empty line, and local/foo being out of position.

// In b.go
import (
	"os"
	
	"testing"
	
	"local/bar"
	
	"github.com/Sirupsen/logrus"
	"golang.org/x/net/context"
	"local/foo"
)

Either install by running go install github.com/vasi-stripe/gogroup/cmd/gogroup@latest (>= go 1.17), go get github.com/vasi-stripe/gogroup/cmd/gogroup (< go 1.17) or, if you have cloned the code, run go install ./... from the cloned dir.

Check which files validate this order:

bash$ gogroup -order std,prefix=local/,other a.go b.go
b.go:6: Extra empty line inside import group at "testing"
bash$ echo $?
3

Fixup files to match this order:

bash$ gogroup -order std,prefix=local/,other -rewrite a.go b.go
Fixed b.go.

Then check git diff, to ensure that nothing broke. Now b.go should look like a.go.

The following import structures are currently supported:

1. A single import declaration, without parens:

   // Optional comment
   import "foo"

2. A single import declaration with parens:

   // Optional comment
   import (
     "something" // Optional comment
     
     // Optional comment
     "another/thing"
     "one/more/thing"
     name "import/with/name"
     . "dot/import"
   )

All of these allow doc comments and named imports.

• Write tests, check coverage
• Improve validation messages
• Figure out what to do with different structures:

  • Multiple import declarations. Are these allowed? Do we merge these together?

     import (
     	"something"
     )
     import (
     	"another/thing"
     )

  • Spaces at start/end of import declaration. Get rid of them?

     import (
    
     	"something"
    
     )

  • Random comments. Are these allowed? If we move things around, where do these comments end up?

     import (
     	"something"
     	
     	// Random comment in the middle.
     	
     	// Normal doc comment, this is already ok.
     	"another/thing"
     	// Trailing comment.
     )
     
     // Comment in the middle of import declarations.
     
     // Normal doc comment, this is ok.
     import (
     	"something/else"
     )

  • import "C" statements. We should try hard to keep these separate from other imports.

     import (
     	"something"
     )
     
     // Random comment.
     
     // #cgo CFLAGS: -DPNG_DEBUG=1
     // #cgo amd64 386 CFLAGS: -DX86=1
     // #cgo LDFLAGS: -lpng
     // #include <png.h>
     import "C"
    
     import (
     	"another/thing"
     )