cli/command/completion: change Platforms to return a cobra.CompletionFunc

It's adding a slight indirection by constructing a function when called,
but makes the completion functions more consistent, the signature easier
to read, and making the return type a [cobra.CompletionFunc] makes it
more transparent what it's intended for, and helps discovery of functions
that provide completion.

[cobra.CompletionFunc]: https://pkg.go.dev/github.com/spf13/cobra#CompletionFunc

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/completion/functions.go

@@ -177,6 +177,8 @@ var commonPlatforms = []string{
 //   - we currently exclude architectures that may have unofficial builds,
 //     but don't have wide adoption (and no support), such as loong64, mipsXXX,
 //     ppc64 (non-le) to prevent confusion.
-func Platforms(_ *cobra.Command, _ []string, _ string) (platforms []string, _ cobra.ShellCompDirective) {
-	return commonPlatforms, cobra.ShellCompDirectiveNoFileComp
+func Platforms() cobra.CompletionFunc {
+	return func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		return commonPlatforms, cobra.ShellCompDirectiveNoFileComp
+	}
 }

cli/command/completion/functions_test.go

@@ -304,7 +304,7 @@ func TestCompleteNetworkNames(t *testing.T) {
 }
 
 func TestCompletePlatforms(t *testing.T) {
-	values, directives := Platforms(nil, nil, "")
+	values, directives := Platforms()(nil, nil, "")
 	assert.Check(t, is.Equal(directives&cobra.ShellCompDirectiveNoFileComp, cobra.ShellCompDirectiveNoFileComp), "Should not perform file completion")
 	assert.Check(t, is.DeepEqual(values, commonPlatforms))
 }