We're not adding a flag.

I'm pretty sure goimports already correctly handles this case, and we have tests for it too.

Note that permission denied error in your log?

I suspect that goimports is unable to scan your $GOPATH so it's unable to learn that a/packg is package surprise and thus it falls back to assuming you named it conventionally, and then it discards it.

Fix your permission error and then let's see what happens.

Couldn't figure out yet why there's a permission denied but saw with debugging that goimports walks through the $GOPATH. The 2nd line also shows that it could retrieve the package name:

importPathToNameGoPathParse("a/packg", srcDir="/Users/dominik/go/src/a") = "surprise", <nil>

Anyway, I worked around the permission denied and now see this extra helpful lines (full output below):

packg candidate 1/1: a/packg in /tmp/src/a/packg
loading exports in dir /tmp/src/a/packg (seeking package packg)
scan of dir /tmp/src/a/packg is not expected package packg (actually surprise)

However, these lines don't seem enough that an IDE can (easily) act on to show the deletion reason at the former line import "a/packg", does it? At least a hint to the file & line of the import in question would be helpful.

Sidenote: The 3 lines above don't show up if you use the imported package correctly, e.g. like this:

package main

import "a/packg"

func main() {
	surprise.SomeFunc()
}

Full output (from GOPATH=/tmp/ goimports -v main.go):

2017/12/20 11:47:42.591341 fixImports(filename="main.go"), abs="/tmp/src/a/main.go", srcDir="/tmp/src/a" ...
2017/12/20 11:47:42.591652 importPathToNameGoPathParse("a/packg", srcDir="/tmp/src/a") = "surprise", <nil>
2017/12/20 11:47:42.591796 open /tmp/src/.goimportsignore: no such file or directory
2017/12/20 11:47:42.591808 scanning $GOPATH
2017/12/20 11:47:42.591869 scanning $GOROOT
2017/12/20 11:47:42.592148 scanned $GOPATH
2017/12/20 11:47:42.601379 scanned $GOROOT
2017/12/20 11:47:42.602617 packg candidate 1/1: a/packg in /tmp/src/a/packg
2017/12/20 11:47:42.602652 loading exports in dir /tmp/src/a/packg (seeking package packg)
2017/12/20 11:47:42.603156 scan of dir /tmp/src/a/packg is not expected package packg (actually surprise)
package main

func main() {
	packg.SomeFunc()
}

However, these lines don't seem enough that an IDE can (easily) act on to show the deletion reason at the former line import "a/packg", does it? At least a hint to the file & line of the import in question would be helpful.

Those lines are for people debugging goimports while developing goimports. They're not for users or IDEs.

It looks like everything is happening properly: when you don't use the import it's removed, and when you do use it, it's not removed.

You want to get warnings, but goimports isn't in the business of warnings.

That is probably the job of a lint tool, as it's more of a style issue.

I'm going to close this, as I see nothing for goimports to do. Let me know if I misunderstand, though.