Imports for Go package splitted into files

If I need an import in two or more files for one package in Go, what is the idiomatic way?

Until today I do it like this:

file1.go

package A

import "os"

file2.go

package A

import "os"

It's not a question of being idiomatic, it's a question of scopes.

Import declarations are scoped to the containing file. Spec: Import declarations:

> An import declaration states that the source file containing the declaration depends on functionality of the imported package (§Program initialization and execution) and enables access to exported identifiers of that package.

Also Spec: Declarations and scope:

> Go is lexically scoped using blocks:
> ...
> 3. The scope of the package name of an imported package is the file block of the file containing the import declaration.
> ...

What this means is that if there's a package that is needed in multiple files (forming a single package or multiple, it doesn't matter), you have to import it separately in all of those files.

What you should do is review and revise how you separate code between files, because it may be a good way to group functions and declarations into the same file that have the same dependencies (that depend on the same set of packages), and so you would only need to import those packages once.

Also note that if certain files of package mypkg depend on a set of other packages, but not the other files of mypkg, it may also be profitable to split mypkg into 2 separate packages based on the dependencies. Most of these decisions are subjective though, you have tell if they make sense in your case or not.