fix docker info --format=json not outputting json format

The --format=json option was added for all inspect commands, but was not implemented
for "docker info". This patch implements the missing option.

Before this patch:

    docker info --format=json
    json

With this patch applied:

    docker info --format=json
    {"ID":"80c2f18a-2c88-4e4a-ba69-dca0eea59835","Containers":7,"ContainersRunning":"..."}

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

Author: thaJeztah

cli/command/system/info.go

@@ -12,7 +12,9 @@ import (
 	pluginmanager "github.com/docker/cli/cli-plugins/manager"
 	"github.com/docker/cli/cli/command"
 	"github.com/docker/cli/cli/command/completion"
+	"github.com/docker/cli/cli/command/formatter"
 	"github.com/docker/cli/cli/debug"
+	flagsHelper "github.com/docker/cli/cli/flags"
 	"github.com/docker/cli/templates"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/swarm"
@@ -62,10 +64,7 @@ func NewInfoCommand(dockerCli command.Cli) *cobra.Command {
 		ValidArgsFunction: completion.NoComplete,
 	}
 
-	flags := cmd.Flags()
-
-	flags.StringVarP(&opts.format, "format", "f", "", "Format the output using the given Go template")
-
+	cmd.Flags().StringVarP(&opts.format, "format", "f", "", flagsHelper.InspectFormatHelp)
 	return cmd
 }
 
@@ -507,6 +506,10 @@ func printServerWarningsLegacy(dockerCli command.Cli, info types.Info) {
 }
 
 func formatInfo(dockerCli command.Cli, info info, format string) error {
+	if format == formatter.JSONFormatKey {
+		format = formatter.JSONFormat
+	}
+
 	// Ensure slice/array fields render as `[]` not `null`
 	if info.ClientInfo != nil && info.ClientInfo.Plugins == nil {
 		info.ClientInfo.Plugins = make([]pluginmanager.Plugin, 0)

cli/command/system/info_test.go

@@ -396,6 +396,11 @@ func TestPrettyPrintInfo(t *testing.T) {
 				assert.NilError(t, formatInfo(cli, tc.dockerInfo, "{{json .}}"))
 				golden.Assert(t, cli.OutBuffer().String(), tc.jsonGolden+".json.golden")
 				assert.Check(t, is.Equal("", cli.ErrBuffer().String()))
+
+				cli = test.NewFakeCli(&fakeClient{})
+				assert.NilError(t, formatInfo(cli, tc.dockerInfo, "json"))
+				golden.Assert(t, cli.OutBuffer().String(), tc.jsonGolden+".json.golden")
+				assert.Check(t, is.Equal("", cli.ErrBuffer().String()))
 			}
 		})
 	}

docs/reference/commandline/info.md

@@ -9,9 +9,9 @@ Display system-wide information
 
 ### Options
 
-| Name                                   | Type     | Default | Description                                   |
-|:---------------------------------------|:---------|:--------|:----------------------------------------------|
-| [`-f`](#format), [`--format`](#format) | `string` |         | Format the output using the given Go template |
+| Name                                   | Type     | Default | Description                                                                                                                                                                                                                                                        |
+|:---------------------------------------|:---------|:--------|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| [`-f`](#format), [`--format`](#format) | `string` |         | Format output using a custom template:<br>'json':             Print in JSON format<br>'TEMPLATE':         Print output using the given Go template.<br>Refer to https://docs.docker.com/go/formatting/ for more information about formatting output with templates |
 
 
 <!---MARKER_GEN_END-->

docs/reference/commandline/system_info.md

@@ -9,9 +9,9 @@ Display system-wide information
 
 ### Options
 
-| Name             | Type     | Default | Description                                   |
-|:-----------------|:---------|:--------|:----------------------------------------------|
-| `-f`, `--format` | `string` |         | Format the output using the given Go template |
+| Name             | Type     | Default | Description                                                                                                                                                                                                                                                        |
+|:-----------------|:---------|:--------|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `-f`, `--format` | `string` |         | Format output using a custom template:<br>'json':             Print in JSON format<br>'TEMPLATE':         Print output using the given Go template.<br>Refer to https://docs.docker.com/go/formatting/ for more information about formatting output with templates |
 
 
 <!---MARKER_GEN_END-->