cmd/docker: add tests for flag-completions, and refactor

Remove the registerCompletionFuncForGlobalFlags for now, as
the error it returned was ignored, so it didn't add much
benefit, other than abstracting things.

Split the underlying completion-functions to separate
functions, and add some basic tests for them.

Remove the completions helper, as it now didn't add much,
and it saved having the dependency on the package.

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

cmd/docker/completions.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"github.com/docker/cli/cli/command/completion"
 	"github.com/docker/cli/cli/context/store"
 	"github.com/spf13/cobra"
 )
@@ -10,18 +9,15 @@ type contextStoreProvider interface {
 	ContextStore() store.Store
 }
 
-func registerCompletionFuncForGlobalFlags(dockerCLI contextStoreProvider, cmd *cobra.Command) error {
+func completeContextNames(dockerCLI contextStoreProvider) func(*cobra.Command, []string, string) ([]string, cobra.ShellCompDirective) {
-	err := cmd.RegisterFlagCompletionFunc("context", func(*cobra.Command, []string, string) ([]string, cobra.ShellCompDirective) {
+	return func(*cobra.Command, []string, string) ([]string, cobra.ShellCompDirective) {
 		names, _ := store.Names(dockerCLI.ContextStore())
 		return names, cobra.ShellCompDirectiveNoFileComp
-	})
-	if err != nil {
-		return err
 	}
-	err = cmd.RegisterFlagCompletionFunc("log-level", completion.FromList("debug", "info", "warn", "error", "fatal"))
-	if err != nil {
-		return err
 }
 
-	return nil
+var logLevels = []string{"debug", "info", "warn", "error", "fatal", "panic"}
+
+func completeLogLevels(*cobra.Command, []string, string) ([]string, cobra.ShellCompDirective) {
+	return cobra.FixedCompletions(logLevels, cobra.ShellCompDirectiveNoFileComp)(nil, nil, "")
 }

cmd/docker/completions_test.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/docker/cli/cli/context/store"
+	"github.com/spf13/cobra"
+	"gotest.tools/v3/assert"
+	is "gotest.tools/v3/assert/cmp"
+)
+
+type fakeCLI struct {
+	contextStore store.Store
+}
+
+func (c *fakeCLI) ContextStore() store.Store {
+	return c.contextStore
+}
+
+type fakeContextStore struct {
+	store.Store
+	names []string
+}
+
+func (f fakeContextStore) List() (c []store.Metadata, _ error) {
+	for _, name := range f.names {
+		c = append(c, store.Metadata{Name: name})
+	}
+	return c, nil
+}
+
+func TestCompleteContextNames(t *testing.T) {
+	expectedNames := []string{"context-b", "context-c", "context-a"}
+	cli := &fakeCLI{
+		contextStore: fakeContextStore{
+			names: expectedNames,
+		},
+	}
+
+	values, directives := completeContextNames(cli)(nil, nil, "")
+	assert.Check(t, is.Equal(directives, cobra.ShellCompDirectiveNoFileComp))
+	assert.Check(t, is.DeepEqual(values, expectedNames))
+}
+
+func TestCompleteLogLevels(t *testing.T) {
+	values, directives := completeLogLevels(nil, nil, "")
+	assert.Check(t, is.Equal(directives, cobra.ShellCompDirectiveNoFileComp))
+	assert.Check(t, is.DeepEqual(values, logLevels))
+}

cmd/docker/docker.go

@@ -100,7 +100,11 @@ func newDockerCommand(dockerCli *command.DockerCli) *cli.TopLevelCommand {
 	cmd.SetErr(dockerCli.Err())
 
 	opts, helpCmd = cli.SetupRootCommand(cmd)
-	_ = registerCompletionFuncForGlobalFlags(dockerCli, cmd)
+
+	// TODO(thaJeztah): move configuring completion for these flags to where the flags are added.
+	_ = cmd.RegisterFlagCompletionFunc("context", completeContextNames(dockerCli))
+	_ = cmd.RegisterFlagCompletionFunc("log-level", completeLogLevels)
+
 	cmd.Flags().BoolP("version", "v", false, "Print version information and quit")
 	setFlagErrorFunc(dockerCli, cmd)