fix(features): keep JS property order in metadata, options and compose env

docs/DIVERGENCES.md

@@ -117,9 +117,10 @@ touches a compared surface, reflected in the parity matrix.
   order (`pickFeatureProperties` for a Feature, `pickConfigProperties` for the
   configuration) and `&`, `<`, `>` unescaped, as in TS. Within a property's object value
   (a mount object, `customizations`, `portsAttributes`, …) the keys are sorted, because a
-  decoded Go map keeps no order, where TS keeps the order they were written in; an entry
-  given in another order (a base image's label written by another tool) is likewise
-  rewritten in pick order. The parsed metadata is the same; only the label's bytes differ
+  decoded Go map keeps no order, where TS keeps the order they were written in;
+  `containerEnv` alone keeps TS's order (the array-index keys ascending, then the others
+  as written). An entry given in another order (a base image's label written by another
+  tool) is likewise rewritten in pick order. The parsed metadata is the same; only the label's bytes differ
   (`internal/imagemeta/testdata/ts-oracle/imagemeta.json` records both cases).
 - **Command results write nested objects with their keys sorted.** TS writes each result
   with `JSON.stringify`, so properties come in insertion order. Go matches that order for

docs/parity/parity-matrix.yaml

@@ -199,6 +199,19 @@ initial_cases:
     notes: "readLockfile rethrows JSON.parse's SyntaxError and runAsyncHandler console.errors it: 'SyntaxError: Expected ',' or '}' after property value in JSON at position 15 (line 1 column 16)' on stderr, exit 1, nothing on stdout. Go used to ignore the lockfile and print the graph."
 
   # --- Wave A: new cases (some uncovered divergences, now fixed) ---
+  - id: features.resolve-dependencies-option-key-order-success
+    lane: contract
+    command: features
+    priority: p1
+    docker_required: false
+    setup_cmd: "WORKSPACE=/tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}; rm -rf $WORKSPACE; mkdir -p $WORKSPACE/.devcontainer/f $WORKSPACE/.devcontainer/g; printf '%s' '{\"id\":\"f\",\"version\":\"1.0.0\",\"dependsOn\":{\"./g\":{\"yy\":\"1\",\"3\":\"d\",\"bb\":\"2\"}}}' > $WORKSPACE/.devcontainer/f/devcontainer-feature.json; printf '%s' '{\"id\":\"g\",\"version\":\"1.0.0\"}' > $WORKSPACE/.devcontainer/g/devcontainer-feature.json; printf '%s' '{\"image\":\"alpine:3\",\"features\":{\"./f\":{\"zz\":\"1\",\"10\":\"t\",\"a\":\"b\",\"2\":\"s\"}}}' > $WORKSPACE/.devcontainer/devcontainer.json; echo WORKSPACE=$WORKSPACE"
+    cleanup_cmd: "rm -rf /tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}"
+    ts_cmd: "features resolve-dependencies --workspace-folder ${WORKSPACE}"
+    asserts: [exit_code, stdout_text]
+    class: output-shape
+    current_status: match
+    notes: "installOrder's options are each Feature's value, the user's options object from devcontainer.json or the dependsOn options from devcontainer-feature.json, as JSON.parse built it: the array-index keys first, ascending, then the others as declared. Go sorted them."
+
   - id: features-publish.missing-required
     lane: contract
     command: features-publish
@@ -1135,6 +1148,20 @@ initial_cases:
     current_status: match
     notes: "TS getDevcontainerMetadata writes the Feature's raw values to the devcontainer.metadata label (imageMetadata.ts uses .raw), so a Feature mount and lifecycle command keep ${localEnv:HOME} and are resolved on the host that runs `up`. Go resolved the Feature's mounts before building the label, baking the build host's HOME into the image."
 
+  - id: build.metadata-label-container-env-order-success
+    lane: runtime
+    command: build
+    priority: p1
+    docker_required: true
+    setup_cmd: "WORKSPACE=/tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}; IMG=parity-env-base-${PARITY_CASE_ID}-${PARITY_SIDE}; rm -rf $WORKSPACE; mkdir -p $WORKSPACE/img $WORKSPACE/.devcontainer/f; printf 'FROM alpine:3\\nLABEL devcontainer.metadata=\\047[{\"containerEnv\":{\"ZB\":\"base\",\"10\":\"base\",\"AB\":\"base\"}}]\\047\\n' > $WORKSPACE/img/Dockerfile; docker build -q -t $IMG $WORKSPACE/img >/dev/null; printf '%s' '{\"id\":\"f\",\"version\":\"1.0.0\"}' > $WORKSPACE/.devcontainer/f/devcontainer-feature.json; printf '#!/bin/sh\\ntrue\\n' > $WORKSPACE/.devcontainer/f/install.sh; chmod +x $WORKSPACE/.devcontainer/f/install.sh; printf '%s' '{\"image\":\"'$IMG'\",\"containerEnv\":{\"ZED\":\"cfg\",\"AB\":\"cfg\",\"2\":\"cfg\",\"ALPHA\":\"cfg\"},\"features\":{\"./f\":{}}}' > $WORKSPACE/.devcontainer/devcontainer.json; echo WORKSPACE=$WORKSPACE"
+    ts_cmd: "build --workspace-folder ${WORKSPACE} --image-name parity-${PARITY_CASE_ID}-${PARITY_SIDE}"
+    verify_cmd: "docker image inspect -f '{{index .Config.Labels \"devcontainer.metadata\"}}' ${IMAGE_NAME}"
+    cleanup_cmd: "docker rmi -f parity-${PARITY_CASE_ID}-${PARITY_SIDE} parity-env-base-${PARITY_CASE_ID}-${PARITY_SIDE} >/dev/null 2>&1; rm -rf /tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}; true"
+    asserts: [exit_code, stdout_normalized]
+    class: build-runtime
+    current_status: match
+    notes: "TS getDevcontainerMetadata writes the base image's entries as JSON.parse read them from its label and the config's raw containerEnv as devcontainer.json declares it, so each containerEnv keeps JS property order (the array-index keys 2 and 10 first, ascending, then the others as declared). Go sorted each entry's containerEnv (10 before 2, AB before ZB, ALPHA before ZED)."
+
   - id: up.compose-feature-host-variables-raw-label-success
     lane: runtime
     command: up
@@ -1149,6 +1176,20 @@ initial_cases:
     current_status: match
     notes: "The compose service's image and container labels keep the Feature's ${localEnv:HOME} raw, as TS writes them; the bind mount the container gets is resolved on this host (TS getDevcontainerMetadata's featureRaw.map(substitute)). Go resolved the Feature's mounts before building the label."
 
+  - id: up.compose-container-env-order-success
+    lane: runtime
+    command: up
+    priority: p1
+    docker_required: true
+    setup_cmd: "WORKSPACE=/tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}; IMG=parity-env-base-${PARITY_CASE_ID}-${PARITY_SIDE}; USER_DATA_FOLDER=$WORKSPACE/user-data; rm -rf $WORKSPACE; mkdir -p $WORKSPACE/img $WORKSPACE/.devcontainer/f $USER_DATA_FOLDER; printf 'FROM alpine:3\\nLABEL devcontainer.metadata=\\047[{\"containerEnv\":{\"ZB\":\"base\",\"10\":\"base\",\"AB\":\"base\"}}]\\047\\n' > $WORKSPACE/img/Dockerfile; docker build -q -t $IMG $WORKSPACE/img >/dev/null; printf '%s' '{\"id\":\"f\",\"version\":\"1.0.0\"}' > $WORKSPACE/.devcontainer/f/devcontainer-feature.json; printf '#!/bin/sh\\ntrue\\n' > $WORKSPACE/.devcontainer/f/install.sh; chmod +x $WORKSPACE/.devcontainer/f/install.sh; printf 'services:\\n  app:\\n    image: %s\\n    command: sleep infinity\\n' $IMG > $WORKSPACE/.devcontainer/docker-compose.yml; printf '%s' '{\"dockerComposeFile\":\"docker-compose.yml\",\"service\":\"app\",\"workspaceFolder\":\"/\",\"containerEnv\":{\"ZED\":\"cfg\",\"AB\":\"cfg\",\"2\":\"cfg\",\"ALPHA\":\"cfg\"},\"features\":{\"./f\":{}}}' > $WORKSPACE/.devcontainer/devcontainer.json; echo WORKSPACE=$WORKSPACE; echo USER_DATA_FOLDER=$USER_DATA_FOLDER"
+    ts_cmd: "up --workspace-folder ${WORKSPACE} --skip-post-create --update-remote-user-uid-default never --id-label parity.case=${PARITY_CASE_ID}-${PARITY_SIDE} --user-data-folder ${USER_DATA_FOLDER}"
+    verify_cmd: "grep -A6 '^    environment:' ${USER_DATA_FOLDER}/docker-compose/docker-compose.devcontainer.containerFeatures-*; docker inspect -f '{{index .Config.Labels \"devcontainer.metadata\"}}' ${CONTAINER_ID}; docker image inspect -f '{{index .Config.Labels \"devcontainer.metadata\"}}' $(docker inspect -f '{{.Image}}' ${CONTAINER_ID})"
+    cleanup_cmd: "docker compose --project-name ${COMPOSE_PROJECT_NAME} -f ${WORKSPACE}/.devcontainer/docker-compose.yml down -t 0 >/dev/null 2>&1; docker rmi -f parity-env-base-${PARITY_CASE_ID}-${PARITY_SIDE} >/dev/null 2>&1; rm -rf /tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}; true"
+    asserts: [exit_code, stdout_normalized]
+    class: up-runtime
+    current_status: match
+    notes: "TS writes the compose override's environment from the merged containerEnv (mergeConfiguration's Object.assign over the base image's label, the Features and the config): a key keeps the position it first had, the array-index keys 2 and 10 first, and the value of the last entry that sets it. The container and image labels keep each entry's containerEnv in JS property order. Go sorted the environment and each label entry's containerEnv."
+
   - id: read-configuration.feature-host-variables-merged-success
     lane: runtime
     command: read-configuration
@@ -1396,6 +1437,20 @@ initial_cases:
     current_status: match
     notes: "A local Feature entry is devcontainer-feature.json as JSON.parse reads it, every property kept (keywords, x, empty, an empty option), a repeated one at its first position with its last value, the array-index properties 2 and 10 first, numbers as JS writes them (1.5), and the options' properties in the file's order; then name, value, included, cachePath and consecutiveId (processFeatureIdentifier, fetchFeatures). updateFromOldProperties (containerFeaturesConfiguration.ts) moves extensions and settings into customizations.vscode, settings spread under vscode's. Go used to write only the properties it has fields for, in the struct's order, with options sorted and the deprecated properties dropped."
 
+  - id: read-configuration.features-configuration-value-key-order-success
+    lane: contract
+    command: read-configuration
+    priority: p1
+    docker_required: false
+    setup_cmd: "WORKSPACE=/tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}; rm -rf $WORKSPACE; mkdir -p $WORKSPACE/.devcontainer/f; printf '%s' '{\"id\":\"f\",\"version\":\"1.0.0\",\"options\":{\"a\":{\"type\":\"string\",\"default\":\"z\"}}}' > $WORKSPACE/.devcontainer/f/devcontainer-feature.json; printf '%s\\n' '#!/bin/sh' 'true' > $WORKSPACE/.devcontainer/f/install.sh; printf '%s' '{\"image\":\"alpine:3\",\"features\":{\"./f\":{\"zz\":\"1\",\"10\":\"t\",\"a\":\"b\",\"2\":\"s\"}}}' > $WORKSPACE/.devcontainer/devcontainer.json; echo WORKSPACE=$WORKSPACE"
+    cleanup_cmd: "rm -rf /tmp/parity-${PARITY_CASE_ID}-${PARITY_SIDE}"
+    ts_cmd: "read-configuration --workspace-folder ${WORKSPACE} --include-features-configuration"
+    key_order: ["featuresConfiguration.featureSets.0.features.0.value"]
+    asserts: [exit_code, stdout_normalized]
+    class: output-shape
+    current_status: match
+    notes: "A Feature's value is the user's options object from devcontainer.json as JSON.parse built it, so it keeps JS property order: the array-index keys 2 and 10 first, ascending, then zz and a as declared. Go sorted it (10, 2, a, zz)."
+
   - id: read-configuration.features-configuration-oci-feature-key-order-success
     lane: runtime
     command: read-configuration

internal/cli/build.go

@@ -186,7 +186,7 @@ func runBuild(ctx context.Context, out Output, opts *buildOpts) error {
 	defer engine.Close()
 
 	run := &buildRunner{log: logger, docker: dockerClient, engine: engine, opts: opts}
-	if run.configLabel, err = configLabelEntry(loadResult.RawConfig, false); err != nil {
+	if run.configLabel, err = configLabelEntry(loadResult.RawConfig, loadResult.Config.ContainerEnvOrder, false); err != nil {
 		return writeErrorResult(out, err.Error())
 	}
 

internal/cli/compose_override.go

@@ -6,9 +6,9 @@ import (
 	"fmt"
 	"os"
 	"regexp"
-	"slices"
 	"strings"
 
+	"github.com/devcontainers/cli/internal/features"
 	"github.com/devcontainers/cli/internal/imagemeta"
 )
 
@@ -212,12 +212,7 @@ func generateComposeFeaturesOverride(in composeFeaturesOverride) string {
 	}
 	if len(merged.ContainerEnv) > 0 {
 		b.WriteString("\n    environment:")
-		keys := make([]string, 0, len(merged.ContainerEnv))
-		for k := range merged.ContainerEnv {
-			keys = append(keys, k)
-		}
-		slices.Sort(keys)
-		for _, k := range keys {
+		for _, k := range features.PropertyOrder(merged.ContainerEnv, merged.ContainerEnvOrder) {
 			v := strings.ReplaceAll(merged.ContainerEnv[k], "\n", `\n`)
 			v = escapeComposeDollar(v)
 			v = strings.ReplaceAll(v, "'", "''")

internal/cli/compose_override_test.go

@@ -215,3 +215,19 @@ func TestComposeFeaturesBuild(t *testing.T) {
 		t.Errorf("label-only content = %q, want %q", label.DockerfileContent, want)
 	}
 }
+
+func TestGenerateComposeFeaturesOverrideWritesTheMergedEnvInPropertyOrder(t *testing.T) {
+	entries := imagemeta.ReadMetadataFromLabels(map[string]string{
+		imagemeta.MetadataLabel: `[{"containerEnv":{"ZB":"base","10":"base","AB":"base"}}]`,
+	}, nil)
+	entries = append(entries, imagemeta.Entry{
+		ContainerEnv:      map[string]string{"ZED": "cfg", "AB": "cfg", "2": "cfg", "ALPHA": "cfg"},
+		ContainerEnvOrder: []string{"ZED", "AB", "2", "ALPHA"},
+	})
+	got := generateComposeFeaturesOverride(composeFeaturesOverride{Service: "app", Merged: imagemeta.MergeConfiguration(entries)})
+	_, env, _ := strings.Cut(got, "    environment:\n")
+	want := "      - '2=cfg'\n      - '10=base'\n      - 'ZB=base'\n      - 'AB=cfg'\n      - 'ZED=cfg'\n      - 'ALPHA=cfg'\n"
+	if env != want {
+		t.Errorf("environment:\n%s\nwant:\n%s", env, want)
+	}
+}

internal/cli/features_resolve_deps.go

@@ -81,7 +81,9 @@ func realFeaturesResolveDepsCmd() *cobra.Command {
 				}
 				var opts any
 				if len(fs.Features) > 0 {
-					opts = fs.Features[0].Value
+					if opts, err = features.JSValue(fs.Features[0].Value, fs.Features[0].ValueOrder); err != nil {
+						return err
+					}
 				}
 				entries = append(entries, installEntry{ID: id, Options: opts})
 			}

internal/cli/metadata_label.go

@@ -17,7 +17,7 @@ var labelConfigProperties = []string{
 	"otherPortsAttributes", "forwardPorts", "shutdownAction", "updateRemoteUserUID", "hostRequirements",
 }
 
-func configLabelEntry(raw map[string]any, omitRemoteEnv bool) (imagemeta.Entry, error) {
+func configLabelEntry(raw map[string]any, envOrder []string, omitRemoteEnv bool) (imagemeta.Entry, error) {
 	picked := map[string]any{}
 	for _, k := range labelConfigProperties {
 		if v, ok := raw[k]; ok && (!omitRemoteEnv || k != "remoteEnv") {
@@ -32,6 +32,7 @@ func configLabelEntry(raw map[string]any, omitRemoteEnv bool) (imagemeta.Entry,
 	if err != nil {
 		return imagemeta.Entry{}, fmt.Errorf("devcontainer.metadata entry of the configuration: %w", err)
 	}
+	entry.ContainerEnvOrder = envOrder
 	return entry, nil
 }
 
@@ -75,6 +76,9 @@ func hostMetadataSubstitution(hostSub config.HostSubContext, idLabels []string)
 		if err != nil {
 			return err
 		}
+		for i := range resolved {
+			resolved[i].ContainerEnvOrder = (*entries)[i].ContainerEnvOrder
+		}
 		*entries = resolved
 		return nil
 	}

internal/cli/metadata_label_test.go

@@ -25,7 +25,7 @@ func TestConfigLabelEntryPicksTheRawConfig(t *testing.T) {
 	}`), &raw); err != nil {
 		t.Fatal(err)
 	}
-	entry, err := configLabelEntry(raw, false)
+	entry, err := configLabelEntry(raw, nil, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -34,14 +34,14 @@ func TestConfigLabelEntryPicksTheRawConfig(t *testing.T) {
 	if string(got) != want {
 		t.Errorf("entry = %s\nwant    %s", got, want)
 	}
-	omitted, err := configLabelEntry(raw, true)
+	omitted, err := configLabelEntry(raw, nil, true)
 	if err != nil {
 		t.Fatal(err)
 	}
 	if omitted.RemoteEnv != nil {
 		t.Errorf("remoteEnv kept with omitRemoteEnv: %v", omitted.RemoteEnv)
 	}
-	if _, err := configLabelEntry(map[string]any{"init": "yes"}, false); err == nil {
+	if _, err := configLabelEntry(map[string]any{"init": "yes"}, nil, false); err == nil {
 		t.Error("an init that is no boolean: want an error")
 	}
 }
@@ -164,3 +164,28 @@ func TestHostMetadataSubstitutionLeavesTheRawEntriesRaw(t *testing.T) {
 		}
 	}
 }
+
+func TestMetadataEntriesKeepTheContainerEnvOrder(t *testing.T) {
+	raw := map[string]any{"containerEnv": map[string]any{"ZED": "1", "10": "2", "ALPHA": "${localEnv:U}", "2": "4"}}
+	order := []string{"ZED", "10", "ALPHA", "2"}
+	entry, err := configLabelEntry(raw, order, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := `[{"containerEnv":{"2":"4","10":"2","ZED":"1","ALPHA":"${localEnv:U}"}}]`
+	if got := containerMetadataLabel([]imagemeta.Entry{entry}); got != want {
+		t.Errorf("label = %s\nwant    %s", got, want)
+	}
+	entries := []imagemeta.Entry{entry}
+	if err := hostMetadataSubstitution(config.HostSubContext{Env: map[string]string{"U": "me"}}, nil)(&entries); err != nil {
+		t.Fatal(err)
+	}
+	want = `[{"containerEnv":{"2":"4","10":"2","ZED":"1","ALPHA":"me"}}]`
+	if got := containerMetadataLabel(entries); got != want {
+		t.Errorf("substituted label = %s\nwant    %s", got, want)
+	}
+	cfg := &config.DevContainer{ContainerEnv: map[string]string{"ZED": "1", "ALPHA": "3"}, ContainerEnvOrder: []string{"ZED", "ALPHA"}}
+	if got, want := containerMetadataLabel([]imagemeta.Entry{configMetadataEntry(cfg, false)}), `[{"containerEnv":{"ZED":"1","ALPHA":"3"}}]`; got != want {
+		t.Errorf("config entry label = %s\nwant    %s", got, want)
+	}
+}

internal/cli/read_configuration.go

@@ -483,6 +483,7 @@ func configMetadataEntry(cfg *config.DevContainer, omitRemoteEnv bool) imagemeta
 		ShutdownAction:      cfg.ShutdownAction,
 		UpdateRemoteUserUID: cfg.UpdateRemoteUserUID,
 		ContainerEnv:        cfg.ContainerEnv,
+		ContainerEnvOrder:   cfg.ContainerEnvOrder,
 		CapAdd:              cfg.CapAdd,
 		SecurityOpt:         cfg.SecurityOpt,
 		Mounts:              metadataMounts(cfg),

internal/cli/up.go

@@ -315,7 +315,7 @@ func runUp(ctx context.Context, out Output, opts *upOpts) error {
 	}
 	run.idLabels = idLabels
 	run.substitute = hostMetadataSubstitution(loadResult.HostSub, idLabels)
-	if run.configLabel, err = configLabelEntry(loadResult.RawConfig, opts.omitConfigRemoteEnvFromMeta); err != nil {
+	if run.configLabel, err = configLabelEntry(loadResult.RawConfig, loadResult.Config.ContainerEnvOrder, opts.omitConfigRemoteEnvFromMeta); err != nil {
 		return writeErrorResult(out, err.Error())
 	}
 

internal/features/jsobject.go

@@ -179,6 +179,24 @@ func toJS(v any) (any, error) {
 	return parseJS(data)
 }
 
+// JSValue is toJS of v, with the keys of a map v in
+// PropertyOrder(v, declared).
+func JSValue(v any, declared []string) (any, error) {
+	m, ok := v.(map[string]any)
+	if !ok {
+		return toJS(v)
+	}
+	obj := newJSObject()
+	for _, k := range PropertyOrder(m, declared) {
+		js, err := toJS(m[k])
+		if err != nil {
+			return nil, err
+		}
+		obj.set(k, js)
+	}
+	return obj, nil
+}
+
 func jsTruthy(v any) bool {
 	switch x := v.(type) {
 	case nil:

internal/features/jsobject_test.go

@@ -64,3 +64,24 @@ func TestPropertyOrderListsKeysAsObjectKeys(t *testing.T) {
 		t.Errorf("PropertyOrder of an empty map = %v", got)
 	}
 }
+
+func TestJSValueOrdersAMapsKeys(t *testing.T) {
+	for _, tc := range []struct {
+		v     any
+		order []string
+		want  string
+	}{
+		{map[string]any{"zz": "1", "10": "t", "a": map[string]any{"y": 1, "b": 2}, "2": "s", "m": nil}, []string{"zz", "gone", "10", "a", "2"}, `{"2":"s","10":"t","zz":"1","a":{"b":2,"y":1},"m":null}`},
+		{"latest", []string{"x"}, `"latest"`},
+		{true, nil, `true`},
+		{nil, nil, `null`},
+	} {
+		js, err := JSValue(tc.v, tc.order)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got, err := json.Marshal(js); err != nil || string(got) != tc.want {
+			t.Errorf("JSValue(%v, %v) = %s, %v; want %s", tc.v, tc.order, got, err, tc.want)
+		}
+	}
+}

internal/features/types.go

@@ -67,17 +67,18 @@ func (f Feature) MarshalJSON() ([]byte, error) {
 	feature := newJSObject()
 	for _, k := range f.SourceKeys {
 		var v any
+		var order []string
 		switch k {
 		case "id":
 			v = f.ID
 		case "name":
 			v = f.Name
 		case "value":
-			v = f.Value
+			v, order = f.Value, f.ValueOrder
 		case "included":
 			v = f.Included
 		}
-		js, err := toJS(v)
+		js, err := JSValue(v, order)
 		if err != nil {
 			return nil, err
 		}

internal/features/types_order_test.go

@@ -87,3 +87,12 @@ func TestFeatureMarshalJSONMovesDeprecatedProperties(t *testing.T) {
 		t.Error("extensions concatenated onto a number, which has no concat: want an error")
 	}
 }
+
+func TestFeatureMarshalJSONWritesTheValueInPropertyOrder(t *testing.T) {
+	f := Feature{ID: "x", Included: true, SourceKeys: LocalFeatureKeys,
+		Value: map[string]any{"zz": "1", "10": "t", "a": true, "2": "s"}, ValueOrder: []string{"zz", "10", "a", "2"}}
+	got, err := json.Marshal(f)
+	if want := `{"id":"x","name":"","value":{"2":"s","10":"t","zz":"1","a":true},"included":true}`; err != nil || string(got) != want {
+		t.Errorf("got  %s, %v\nwant %s", got, err, want)
+	}
+}