context list: temporarily add ContextType to JSON output

Docker Desktop currently ships with the "cloud integration" wrapper,
which outputs an additional ContextType field in the JSON output.

While this field is non-standard, it made its way into Visual Studio's
Docker integration, which uses this to exclude "aci" and "eci" context
types that are not supported by Visual Studio.

This patch;

- conditionally adds a ContextType field to the JSON output
- but ONLY when using the default "{{json .}}" or "json" formats
  (which are the formats used by Visual Studio)
- if the context is a "aci" or "eci" context, that type is
  preserved, otherwise the default "moby" type is used.

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

cli/command/context/list.go

@@ -66,6 +66,8 @@ func runList(dockerCli command.Cli, opts *listOptions) error {
 				Name:    rawMeta.Name,
 				Current: isCurrent,
 				Error:   err.Error(),
+
+				ContextType: getContextType(nil, opts.format),
 			})
 			continue
 		}
@@ -80,6 +82,8 @@ func runList(dockerCli command.Cli, opts *listOptions) error {
 			Description:    meta.Description,
 			DockerEndpoint: dockerEndpoint.Host,
 			Error:          errMsg,
+
+			ContextType: getContextType(meta.AdditionalFields, opts.format),
 		}
 		contexts = append(contexts, &desc)
 	}
@@ -96,6 +100,8 @@ func runList(dockerCli command.Cli, opts *listOptions) error {
 			Name:    curContext,
 			Current: true,
 			Error:   errMsg,
+
+			ContextType: getContextType(nil, opts.format),
 		})
 	}
 	sort.Slice(contexts, func(i, j int) bool {
@@ -111,6 +117,30 @@ func runList(dockerCli command.Cli, opts *listOptions) error {
 	return nil
 }
 
+// getContextType sets the LegacyContextType field for compatibility with
+// Visual Studio, which depends on this field from the "cloud integration"
+// wrapper.
+//
+// https://github.com/docker/compose-cli/blob/c156ce6da4c2b317174d42daf1b019efa87e9f92/api/context/store/contextmetadata.go#L28-L34
+// https://github.com/docker/compose-cli/blob/c156ce6da4c2b317174d42daf1b019efa87e9f92/api/context/store/store.go#L34-L51
+//
+// TODO(thaJeztah): remove this and [ClientContext.ContextType] once Visual Studio is updated to no longer depend on this.
+func getContextType(meta map[string]any, format string) string {
+	if format != formatter.JSONFormat && format != formatter.JSONFormatKey {
+		// We only need the ContextType field when formatting as JSON,
+		// which is the format-string used by Visual Studio to detect the
+		// context-type.
+		return ""
+	}
+	if ct, ok := meta["Type"]; ok {
+		// If the context on-disk has a context-type (ecs, aci), return it.
+		return ct.(string)
+	}
+
+	// Use the default context-type.
+	return "moby"
+}
+
 func format(dockerCli command.Cli, opts *listOptions, contexts []*formatter.ClientContext) error {
 	contextCtx := formatter.Context{
 		Output: dockerCli.Out(),

cli/command/context/testdata/list-json.golden

@@ -1,5 +1,5 @@
-{"Current":false,"Description":"description of context1","DockerEndpoint":"https://someswarmserver.example.com","Error":"","Name":"context1"}
+{"Name":"context1","Description":"description of context1","DockerEndpoint":"https://someswarmserver.example.com","Current":false,"Error":"","ContextType":"aci"}
-{"Current":false,"Description":"description of context2","DockerEndpoint":"https://someswarmserver.example.com","Error":"","Name":"context2"}
+{"Name":"context2","Description":"description of context2","DockerEndpoint":"https://someswarmserver.example.com","Current":false,"Error":"","ContextType":"ecs"}
-{"Current":false,"Description":"description of context3","DockerEndpoint":"https://someswarmserver.example.com","Error":"","Name":"context3"}
+{"Name":"context3","Description":"description of context3","DockerEndpoint":"https://someswarmserver.example.com","Current":false,"Error":"","ContextType":"moby"}
-{"Current":true,"Description":"description of current","DockerEndpoint":"https://someswarmserver.example.com","Error":"","Name":"current"}
+{"Name":"current","Description":"description of current","DockerEndpoint":"https://someswarmserver.example.com","Current":true,"Error":"","ContextType":"moby"}
-{"Current":false,"Description":"Current DOCKER_HOST based configuration","DockerEndpoint":"unix:///var/run/docker.sock","Error":"","Name":"default"}
+{"Name":"default","Description":"Current DOCKER_HOST based configuration","DockerEndpoint":"unix:///var/run/docker.sock","Current":false,"Error":"","ContextType":"moby"}

cli/command/formatter/context.go

@@ -1,5 +1,7 @@
 package formatter
 
+import "encoding/json"
+
 const (
 	// ClientContextTableFormat is the default client context format.
 	ClientContextTableFormat = "table {{.Name}}{{if .Current}} *{{end}}\t{{.Description}}\t{{.DockerEndpoint}}\t{{.Error}}"
@@ -28,6 +30,13 @@ type ClientContext struct {
 	DockerEndpoint string
 	Current        bool
 	Error          string
+
+	// ContextType is a temporary field for compatibility with
+	// Visual Studio, which depends on this from the "cloud integration"
+	// wrapper.
+	//
+	// Deprecated: this type is only for backward-compatibility. Do not use.
+	ContextType string `json:"ContextType,omitempty"`
 }
 
 // ClientContextWrite writes formatted contexts using the Context
@@ -60,6 +69,13 @@ func newClientContextContext() *clientContextContext {
 }
 
 func (c *clientContextContext) MarshalJSON() ([]byte, error) {
+	if c.c.ContextType != "" {
+		// We only have ContextType set for plain "json" or "{{json .}}" formatting,
+		// so we should be able to just use the default json.Marshal with no
+		// special handling.
+		return json.Marshal(c.c)
+	}
+	// FIXME(thaJeztah): why do we need a special marshal function here?
 	return MarshalJSON(c)
 }