feat: add DROP FOLDER command for removing empty folders

Adds DROP FOLDER 'path' IN Module syntax across the full MDL pipeline
(grammar, AST, visitor, executor, writer). The command refuses to delete
non-empty folders, returning an error with the child unit count.

Closes #46 (partial — adds missing folder cleanup capability)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

mdl/ast/ast_enumeration.go

@@ -27,6 +27,14 @@ type DropModuleStmt struct {
 
 func (s *DropModuleStmt) isStatement() {}
 
+// DropFolderStmt represents: DROP FOLDER 'path' IN Module
+type DropFolderStmt struct {
+	FolderPath string // Folder path (e.g., "Resources/Images")
+	Module     string // Module name
+}
+
+func (s *DropFolderStmt) isStatement() {}
+
 // CreateEnumerationStmt represents: CREATE ENUMERATION Module.Name (values) COMMENT '...'
 type CreateEnumerationStmt struct {
 	Name           QualifiedName

mdl/executor/cmd_folders.go

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: Apache-2.0
+
+// Package executor - DROP FOLDER command
+package executor
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/mendixlabs/mxcli/mdl/ast"
+	"github.com/mendixlabs/mxcli/model"
+)
+
+// execDropFolder handles DROP FOLDER 'path' IN Module statements.
+// The folder must be empty (no child documents or sub-folders).
+func (e *Executor) execDropFolder(s *ast.DropFolderStmt) error {
+	if e.writer == nil {
+		return fmt.Errorf("not connected to a project")
+	}
+
+	// Find the module
+	module, err := e.findModule(s.Module)
+	if err != nil {
+		return fmt.Errorf("module not found: %s", s.Module)
+	}
+
+	// List all folders
+	folders, err := e.reader.ListFolders()
+	if err != nil {
+		return fmt.Errorf("failed to list folders: %w", err)
+	}
+
+	// Walk the folder path to find the target folder
+	parts := strings.Split(s.FolderPath, "/")
+	currentContainerID := module.ID
+
+	var targetFolderID model.ID
+	for i, part := range parts {
+		if part == "" {
+			continue
+		}
+
+		var found bool
+		for _, f := range folders {
+			if f.ContainerID == currentContainerID && f.Name == part {
+				currentContainerID = f.ID
+				if i == len(parts)-1 {
+					targetFolderID = f.ID
+				}
+				found = true
+				break
+			}
+		}
+
+		if !found {
+			return fmt.Errorf("folder not found: '%s' in %s", s.FolderPath, s.Module)
+		}
+	}
+
+	if targetFolderID == "" {
+		return fmt.Errorf("folder not found: '%s' in %s", s.FolderPath, s.Module)
+	}
+
+	// Delete the folder (writer checks if empty)
+	if err := e.writer.DeleteFolder(targetFolderID); err != nil {
+		return fmt.Errorf("failed to delete folder '%s': %w", s.FolderPath, err)
+	}
+
+	e.invalidateHierarchy()
+	fmt.Fprintf(e.output, "Dropped folder: '%s' in %s\n", s.FolderPath, s.Module)
+	return nil
+}

mdl/executor/executor.go

@@ -227,6 +227,8 @@ func (e *Executor) executeInner(stmt ast.Statement) error {
 		return e.execDropJavaAction(s)
 	case *ast.CreateJavaActionStmt:
 		return e.execCreateJavaAction(s)
+	case *ast.DropFolderStmt:
+		return e.execDropFolder(s)
 	case *ast.MoveStmt:
 		return e.execMove(s)
 

mdl/grammar/MDLParser.g4

@@ -251,6 +251,7 @@ dropStatement
     | DROP WORKFLOW qualifiedName
     | DROP IMAGE COLLECTION qualifiedName
     | DROP REST CLIENT qualifiedName
+    | DROP FOLDER STRING_LITERAL IN (qualifiedName | IDENTIFIER)
     ;
 
 renameStatement

mdl/grammar/parser/MDLParser.interp

@@ -665,6 +665,19 @@ func (b *Builder) ExitDropStatement(ctx *parser.DropStatementContext) {
 		b.statements = append(b.statements, &ast.DropRestClientStmt{
 			Name: buildQualifiedName(names[0]),
 		})
+	} else if ctx.FOLDER() != nil {
+		folderPath := unquoteString(ctx.STRING_LITERAL().GetText())
+		// Module can be a qualifiedName or IDENTIFIER
+		var moduleName string
+		if len(names) > 0 {
+			moduleName = getQualifiedNameText(names[0])
+		} else if ctx.IDENTIFIER() != nil {
+			moduleName = ctx.IDENTIFIER().GetText()
+		}
+		b.statements = append(b.statements, &ast.DropFolderStmt{
+			FolderPath: folderPath,
+			Module:     moduleName,
+		})
 	}
 }