refactor: decouple executor from storage layer, extract remaining BSON

Replace *mpr.Reader/*mpr.Writer with backend.FullBackend throughout
executor. Inject BackendFactory to remove mprbackend import from
executor_connect.go. Move all remaining write-path BSON construction
(DataGrid2, filters, cloning, widget property updates) behind backend
interface.

- Remove writer/reader fields from Executor struct
- Add BackendFactory injection pattern for connect/disconnect
- Create mdl/backend/mpr/datagrid_builder.go (1260 lines)
- Add BuildDataGrid2Widget, BuildFilterWidget to WidgetBuilderBackend
- Delete bson_helpers.go, cmd_pages_builder_input_cloning.go,
  cmd_pages_builder_input_datagrid.go, cmd_pages_builder_v3_pluggable.go
- Remaining BSON: 3 read-only files (describe, diff) — WASM-safe

Author: retran

cmd/mxcli/main.go

@@ -9,6 +9,8 @@ import (
 	"os"
 	"strings"
 
+	"github.com/mendixlabs/mxcli/mdl/backend"
+	mprbackend "github.com/mendixlabs/mxcli/mdl/backend/mpr"
 	"github.com/mendixlabs/mxcli/mdl/diaglog"
 	"github.com/mendixlabs/mxcli/mdl/executor"
 	"github.com/mendixlabs/mxcli/mdl/repl"
@@ -194,6 +196,7 @@ func resolveFormat(cmd *cobra.Command, defaultFormat string) string {
 func newLoggedExecutor(mode string) (*executor.Executor, *diaglog.Logger) {
 	logger := diaglog.Init(version, mode)
 	exec := executor.New(os.Stdout)
+	exec.SetBackendFactory(func() backend.FullBackend { return mprbackend.New() })
 	exec.SetLogger(logger)
 	if globalJSONFlag {
 		exec.SetFormat(executor.FormatJSON)

examples/create_datagrid2_page/main.go

@@ -22,6 +22,8 @@ import (
 	"os"
 	"strings"
 
+	"github.com/mendixlabs/mxcli/mdl/backend"
+	mprbackend "github.com/mendixlabs/mxcli/mdl/backend/mpr"
 	"github.com/mendixlabs/mxcli/mdl/executor"
 	"github.com/mendixlabs/mxcli/mdl/visitor"
 )
@@ -51,6 +53,7 @@ func main() {
 
 	// Create the MDL executor with stdout for output
 	exec := executor.New(os.Stdout)
+	exec.SetBackendFactory(func() backend.FullBackend { return mprbackend.New() })
 
 	// Define the MDL script to create a page with DataGrid2
 	// Note: Adjust module name, entity name, and attributes to match your project

mdl/backend/mock/backend.go

@@ -276,6 +276,8 @@ type MockBackend struct {
 	SerializeWidgetToOpaqueFunc     func(w pages.Widget) any
 	SerializeDataSourceToOpaqueFunc func(ds pages.DataSource) any
 	BuildCreateAttributeObjectFunc  func(attributePath string, objectTypeID, propertyTypeID, valueTypeID string) (any, error)
+	BuildDataGrid2WidgetFunc        func(id model.ID, name string, spec backend.DataGridSpec, projectPath string) (*pages.CustomWidget, error)
+	BuildFilterWidgetFunc           func(spec backend.FilterWidgetSpec, projectPath string) (pages.Widget, error)
 
 	// AgentEditorBackend
 	ListAgentEditorModelsFunc               func() ([]*agenteditor.Model, error)

mdl/backend/mock/mock_mutation.go

@@ -3,6 +3,8 @@
 package mock
 
 import (
+	"fmt"
+
 	"github.com/mendixlabs/mxcli/mdl/backend"
 	"github.com/mendixlabs/mxcli/model"
 	"github.com/mendixlabs/mxcli/sdk/pages"
@@ -17,7 +19,7 @@ func (m *MockBackend) OpenPageForMutation(unitID model.ID) (backend.PageMutator,
 	if m.OpenPageForMutationFunc != nil {
 		return m.OpenPageForMutationFunc(unitID)
 	}
-	return nil, nil
+	return nil, fmt.Errorf("MockBackend.OpenPageForMutation not configured")
 }
 
 // ---------------------------------------------------------------------------
@@ -28,7 +30,7 @@ func (m *MockBackend) OpenWorkflowForMutation(unitID model.ID) (backend.Workflow
 	if m.OpenWorkflowForMutationFunc != nil {
 		return m.OpenWorkflowForMutationFunc(unitID)
 	}
-	return nil, nil
+	return nil, fmt.Errorf("MockBackend.OpenWorkflowForMutation not configured")
 }
 
 // ---------------------------------------------------------------------------
@@ -94,3 +96,17 @@ func (m *MockBackend) BuildCreateAttributeObject(attributePath string, objectTyp
 	}
 	return nil, nil
 }
+
+func (m *MockBackend) BuildDataGrid2Widget(id model.ID, name string, spec backend.DataGridSpec, projectPath string) (*pages.CustomWidget, error) {
+	if m.BuildDataGrid2WidgetFunc != nil {
+		return m.BuildDataGrid2WidgetFunc(id, name, spec, projectPath)
+	}
+	return nil, nil
+}
+
+func (m *MockBackend) BuildFilterWidget(spec backend.FilterWidgetSpec, projectPath string) (pages.Widget, error) {
+	if m.BuildFilterWidgetFunc != nil {
+		return m.BuildFilterWidgetFunc(spec, projectPath)
+	}
+	return nil, nil
+}

mdl/backend/mpr/backend.go

@@ -34,6 +34,11 @@ type MprBackend struct {
 	path   string
 }
 
+// New creates a new unconnected MprBackend. Call Connect(path) to open a project.
+func New() *MprBackend {
+	return &MprBackend{}
+}
+
 // Wrap creates an MprBackend that wraps an existing Writer (and its Reader).
 // This is used during migration when the Executor already owns the Writer
 // and we want to expose it through the Backend interface without opening
@@ -75,6 +80,11 @@ func (b *MprBackend) Disconnect() error {
 func (b *MprBackend) IsConnected() bool { return b.writer != nil }
 func (b *MprBackend) Path() string      { return b.path }
 
+// MprReader returns the underlying *mpr.Reader for callers that still
+// require direct SDK access (e.g. linter rules). Prefer Backend methods
+// for new code.
+func (b *MprBackend) MprReader() *mpr.Reader { return b.reader }
+
 func (b *MprBackend) Version() types.MPRVersion                 { return convertMPRVersion(b.reader.Version()) }
 func (b *MprBackend) ProjectVersion() *types.ProjectVersion     { return convertProjectVersion(b.reader.ProjectVersion()) }
 func (b *MprBackend) GetMendixVersion() (string, error)         { return b.reader.GetMendixVersion() }

mdl/backend/mpr/convert.go

@@ -263,36 +263,10 @@ func convertNavMenuItem(in *mpr.NavMenuItem) *types.NavMenuItem {
 // Conversion helpers: mdl/types -> sdk/mpr (for write methods)
 // ---------------------------------------------------------------------------
 
+// unconvertNavProfileSpec is now a pass-through since mpr.NavigationProfileSpec
+// is aliased to types.NavigationProfileSpec.
 func unconvertNavProfileSpec(s types.NavigationProfileSpec) mpr.NavigationProfileSpec {
-	out := mpr.NavigationProfileSpec{
-		LoginPage:    s.LoginPage,
-		NotFoundPage: s.NotFoundPage,
-		HasMenu:      s.HasMenu,
-	}
-	if s.HomePages != nil {
-		out.HomePages = make([]mpr.NavHomePageSpec, len(s.HomePages))
-		for i, hp := range s.HomePages {
-			out.HomePages[i] = mpr.NavHomePageSpec{IsPage: hp.IsPage, Target: hp.Target, ForRole: hp.ForRole}
-		}
-	}
-	if s.MenuItems != nil {
-		out.MenuItems = make([]mpr.NavMenuItemSpec, len(s.MenuItems))
-		for i, mi := range s.MenuItems {
-			out.MenuItems[i] = unconvertNavMenuItemSpec(mi)
-		}
-	}
-	return out
-}
-
-func unconvertNavMenuItemSpec(in types.NavMenuItemSpec) mpr.NavMenuItemSpec {
-	out := mpr.NavMenuItemSpec{Caption: in.Caption, Page: in.Page, Microflow: in.Microflow}
-	if in.Items != nil {
-		out.Items = make([]mpr.NavMenuItemSpec, len(in.Items))
-		for i, sub := range in.Items {
-			out.Items[i] = unconvertNavMenuItemSpec(sub)
-		}
-	}
-	return out
+	return s
 }
 
 func unconvertEntityMemberAccessSlice(in []types.EntityMemberAccess) []mpr.EntityMemberAccess {

mdl/backend/mpr/convert_roundtrip_test.go

@@ -7,6 +7,7 @@ package mprbackend
 
 import (
 	"errors"
+	"reflect"
 	"testing"
 
 	"github.com/mendixlabs/mxcli/mdl/types"
@@ -492,7 +493,9 @@ func TestUnconvertNavMenuItemSpec_Isolated(t *testing.T) {
 			{Caption: "Child", Microflow: "MF2"},
 		},
 	}
-	out := unconvertNavMenuItemSpec(in)
+	// Since mpr.NavMenuItemSpec is aliased to types.NavMenuItemSpec,
+	// unconvert is now a pass-through. Verify the alias holds.
+	var out mpr.NavMenuItemSpec = in
 	if out.Caption != "Parent" || out.Page != "Page1" || out.Microflow != "MF1" {
 		t.Errorf("field mismatch: %+v", out)
 	}
@@ -503,7 +506,7 @@ func TestUnconvertNavMenuItemSpec_Isolated(t *testing.T) {
 
 func TestUnconvertNavMenuItemSpec_NilItems(t *testing.T) {
 	in := types.NavMenuItemSpec{Caption: "Leaf"}
-	out := unconvertNavMenuItemSpec(in)
+	var out mpr.NavMenuItemSpec = in
 	if out.Items != nil {
 		t.Errorf("expected nil Items for leaf: %+v", out.Items)
 	}
@@ -598,3 +601,51 @@ func TestUnconvertImageCollection(t *testing.T) {
 	}
 }
 
+// ============================================================================
+// Field-count drift assertions
+// ============================================================================
+//
+// These tests catch silent field drift: if a struct gains a new field but
+// the convert/unconvert function is not updated, the test fails.
+
+func assertFieldCount(t *testing.T, name string, v any, expected int) {
+	t.Helper()
+	actual := reflect.TypeOf(v).NumField()
+	if actual != expected {
+		t.Errorf("%s field count changed: expected %d, got %d — update convert.go and this test", name, expected, actual)
+	}
+}
+
+func TestFieldCountDrift(t *testing.T) {
+	// mpr → types pairs (manually copied in convert.go).
+	// If a struct gains a field, update the convert function AND this count.
+	assertFieldCount(t, "mpr.FolderInfo", mpr.FolderInfo{}, 3)
+	assertFieldCount(t, "types.FolderInfo", types.FolderInfo{}, 3)
+	assertFieldCount(t, "mpr.UnitInfo", mpr.UnitInfo{}, 4)
+	assertFieldCount(t, "types.UnitInfo", types.UnitInfo{}, 4)
+	assertFieldCount(t, "mpr.RenameHit", mpr.RenameHit{}, 4)
+	assertFieldCount(t, "types.RenameHit", types.RenameHit{}, 4)
+	assertFieldCount(t, "mpr.RawUnit", mpr.RawUnit{}, 4)
+	assertFieldCount(t, "types.RawUnit", types.RawUnit{}, 4)
+	assertFieldCount(t, "mpr.RawUnitInfo", mpr.RawUnitInfo{}, 5)
+	assertFieldCount(t, "types.RawUnitInfo", types.RawUnitInfo{}, 5)
+	assertFieldCount(t, "mpr.RawCustomWidgetType", mpr.RawCustomWidgetType{}, 6)
+	assertFieldCount(t, "types.RawCustomWidgetType", types.RawCustomWidgetType{}, 6)
+	assertFieldCount(t, "mpr.JavaAction", mpr.JavaAction{}, 4)
+	assertFieldCount(t, "types.JavaAction", types.JavaAction{}, 4)
+	assertFieldCount(t, "mpr.JavaScriptAction", mpr.JavaScriptAction{}, 12)
+	assertFieldCount(t, "types.JavaScriptAction", types.JavaScriptAction{}, 12)
+	assertFieldCount(t, "mpr.NavigationDocument", mpr.NavigationDocument{}, 4)
+	assertFieldCount(t, "types.NavigationDocument", types.NavigationDocument{}, 4)
+	assertFieldCount(t, "mpr.JsonStructure", mpr.JsonStructure{}, 8)
+	assertFieldCount(t, "types.JsonStructure", types.JsonStructure{}, 8)
+	assertFieldCount(t, "mpr.JsonElement", mpr.JsonElement{}, 14)
+	assertFieldCount(t, "types.JsonElement", types.JsonElement{}, 14)
+	assertFieldCount(t, "mpr.ImageCollection", mpr.ImageCollection{}, 6)
+	assertFieldCount(t, "types.ImageCollection", types.ImageCollection{}, 6)
+	assertFieldCount(t, "mpr.EntityMemberAccess", mpr.EntityMemberAccess{}, 3)
+	assertFieldCount(t, "types.EntityMemberAccess", types.EntityMemberAccess{}, 3)
+	assertFieldCount(t, "mpr.EntityAccessRevocation", mpr.EntityAccessRevocation{}, 6)
+	assertFieldCount(t, "types.EntityAccessRevocation", types.EntityAccessRevocation{}, 6)
+}
+