cli/command/completion: change EnvVarNames 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

@@ -116,14 +116,16 @@ func NetworkNames(dockerCLI APIClientProvider) cobra.CompletionFunc {
 //	export MY_VAR=hello
 //	docker run --rm --env MY_VAR alpine printenv MY_VAR
 //	hello
-func EnvVarNames(_ *cobra.Command, _ []string, _ string) (names []string, _ cobra.ShellCompDirective) {
-	envs := os.Environ()
-	names = make([]string, 0, len(envs))
-	for _, env := range envs {
-		name, _, _ := strings.Cut(env, "=")
-		names = append(names, name)
+func EnvVarNames() cobra.CompletionFunc {
+	return func(_ *cobra.Command, _ []string, _ string) (names []string, _ cobra.ShellCompDirective) {
+		envs := os.Environ()
+		names = make([]string, 0, len(envs))
+		for _, env := range envs {
+			name, _, _ := strings.Cut(env, "=")
+			names = append(names, name)
+		}
+		return names, cobra.ShellCompDirectiveNoFileComp
 	}
-	return names, cobra.ShellCompDirectiveNoFileComp
 }
 
 // FromList offers completion for the given list of options.

cli/command/completion/functions_test.go

@@ -176,7 +176,7 @@ func TestCompleteEnvVarNames(t *testing.T) {
 		"ENV_A": "hello-a",
 		"ENV_B": "hello-b",
 	})
-	values, directives := EnvVarNames(nil, nil, "")
+	values, directives := EnvVarNames()(nil, nil, "")
 	assert.Check(t, is.Equal(directives&cobra.ShellCompDirectiveNoFileComp, cobra.ShellCompDirectiveNoFileComp), "Should not perform file completion")
 
 	sort.Strings(values)

cli/command/container/completion.go

@@ -122,7 +122,7 @@ func addCompletions(cmd *cobra.Command, dockerCLI completion.APIClientProvider)
 	_ = cmd.RegisterFlagCompletionFunc("cap-add", completeLinuxCapabilityNames)
 	_ = cmd.RegisterFlagCompletionFunc("cap-drop", completeLinuxCapabilityNames)
 	_ = cmd.RegisterFlagCompletionFunc("cgroupns", completeCgroupns())
-	_ = cmd.RegisterFlagCompletionFunc("env", completion.EnvVarNames)
+	_ = cmd.RegisterFlagCompletionFunc("env", completion.EnvVarNames())
 	_ = cmd.RegisterFlagCompletionFunc("env-file", completion.FileNames)
 	_ = cmd.RegisterFlagCompletionFunc("ipc", completeIpc(dockerCLI))
 	_ = cmd.RegisterFlagCompletionFunc("link", completeLink(dockerCLI))

cli/command/container/exec.go

@@ -78,7 +78,7 @@ func newExecCommand(dockerCLI command.Cli) *cobra.Command {
 	flags.StringVarP(&options.Workdir, "workdir", "w", "", "Working directory inside the container")
 	flags.SetAnnotation("workdir", "version", []string{"1.35"})
 
-	_ = cmd.RegisterFlagCompletionFunc("env", completion.EnvVarNames)
+	_ = cmd.RegisterFlagCompletionFunc("env", completion.EnvVarNames())
 	_ = cmd.RegisterFlagCompletionFunc("env-file", completion.FileNames)
 
 	return cmd

cli/command/service/create.go

@@ -82,7 +82,7 @@ func newCreateCommand(dockerCLI command.Cli) *cobra.Command {
 	// _ = cmd.RegisterFlagCompletionFunc(flagStopSignal, completeSignals)
 
 	_ = cmd.RegisterFlagCompletionFunc(flagMode, completion.FromList("replicated", "global", "replicated-job", "global-job"))
-	_ = cmd.RegisterFlagCompletionFunc(flagEnv, completion.EnvVarNames) // TODO(thaJeztah): flagEnvRemove (needs to read current env-vars on the service)
+	_ = cmd.RegisterFlagCompletionFunc(flagEnv, completion.EnvVarNames()) // TODO(thaJeztah): flagEnvRemove (needs to read current env-vars on the service)
 	_ = cmd.RegisterFlagCompletionFunc(flagEnvFile, completion.FileNames)
 	_ = cmd.RegisterFlagCompletionFunc(flagNetwork, completion.NetworkNames(dockerCLI))
 	_ = cmd.RegisterFlagCompletionFunc(flagRestartCondition, completion.FromList("none", "on-failure", "any"))

cli/command/service/update.go

@@ -121,7 +121,7 @@ func newUpdateCommand(dockerCLI command.Cli) *cobra.Command {
 	// _ = cmd.RegisterFlagCompletionFunc(flagCapDrop, completeLinuxCapabilityNames)
 	// _ = cmd.RegisterFlagCompletionFunc(flagStopSignal, completeSignals)
 
-	_ = cmd.RegisterFlagCompletionFunc(flagEnvAdd, completion.EnvVarNames)
+	_ = cmd.RegisterFlagCompletionFunc(flagEnvAdd, completion.EnvVarNames())
 	// TODO(thaJeztah): flagEnvRemove (needs to read current env-vars on the service)
 	_ = cmd.RegisterFlagCompletionFunc("image", completion.ImageNames(dockerCLI, -1))
 	_ = cmd.RegisterFlagCompletionFunc(flagNetworkAdd, completion.NetworkNames(dockerCLI))