I think this is consistent with what @bradfitz said in #18027 (comment).

I don't care either way, but because the code is one way already, I think it's easiest to not change anything. But if others feel strongly, and others want to do the work, I'm also okay with that.

After mulling this, I'm weakly inclined to change it, despite finding non-grouped lone imports more aesthetically appealing. The diff/merge argument is fairly compelling, and keeping grouped imports grouped eliminates a rare but obnoxious class of bugs around comment-handling.

If we change it, I suggest the following (probably obvious but still worth specifying) behavior:

• goimports not rewrite existing non-grouped imports to be grouped, to avoid churn when running goimports on already-goimports-clean code
• when going from some to zero imports, goimports entirely eliminate the import statement (rather than leaving import ())

I'm unlikely to go do this myself soon, but if someone wants to go tackle this, I'll help/review the CL. Test coverage is pretty good, and the relevant bit of code is pretty simple, so this should be a fairly accessible change for someone wanting to learn this codebase (insofar as anything involving goimports is accessible).

I investigated this issue a little.

Just commenting out go/ast/astutil/imports.go#L237 fixes this issue.

} else if len(gen.Specs) == 1 {
	// ...
	gen.Lparen = token.NoPos // drop parens
	// ...
}

This line is originally added in src/cmd/gofix/fix.go https://codereview.appspot.com/4630056/diff/9008/src/cmd/gofix/fix.go#newcode528

Comments nor commit message doesn't say why removing paran, but I assume it just intends to make code simple.

So, option 1 is delete go/ast/astutil/imports.go#L237 line.
I prefer removing it if it's possible, but I guess it's not acceptable change...? At least discussion is required, i guess.

Second option is save import statements are grouped or not and restore parens of a import statement which was originally grouped imports.
I think it's possible but I didn't write code yet and it's going to be complecated compared to option 1.

when going from some to zero imports, goimports entirely eliminate the import statement (rather than leaving import ())

btw, test for this behavior already exists https://github.com/golang/tools/blob/master/imports/fix_test.go#L199-L216

CL https://golang.org/cl/36853 mentions this issue.

I wondered this change may not be accepted because it's a breaking change, but more
I looked into the code, the more I inclined to support to change this behavior.

Especially if there were comments for import statements, it would mess up comments.

// comment 1
import (
	f "fmt"
	// comment 2
	i "io"
)

Removing "fmt" import results in following code in current implementation.

// comment 1

// comment 2
import i "io"

I think it should be

// comment 1
import (
	// comment 2
	i "io"
)