added typeaheead and introspetion

DBSyn/MainView.swift

@@ -6328,6 +6328,8 @@ private struct DBSynSchemaCompareView: View {
     let sourceDatabase: String
     @State private var targetDatabase = ""
     @Environment(\.dismiss) private var dismiss
+    @State private var showMigrationPreview = false
+    @State private var selectedMigrationIDs: Set<String> = []
 
     private var source: DatabaseModel.SchemaIntrospection? { model.introspection(for: sourceDatabase) }
     private var target: DatabaseModel.SchemaIntrospection? { model.introspection(for: targetDatabase) }
@@ -6374,6 +6376,53 @@ private struct DBSynSchemaCompareView: View {
         return items
     }
 
+    // Phase 65: Generate only additive column DDL. Cached introspection does not
+    // contain complete CREATE TABLE or CREATE VIEW definitions, so those objects
+    // are deliberately excluded rather than producing unsafe guesses.
+    private struct Migration: Identifiable {
+        let id: String
+        let label: String
+        let sql: String
+    }
+
+    private func identifier(_ name: String) -> String {
+        "`" + name.replacingOccurrences(of: "`", with: "``") + "`"
+    }
+
+    private var migrations: [Migration] {
+        guard let source, let target, !targetDatabase.isEmpty else { return [] }
+        var result: [Migration] = []
+        let sharedTables = Set(source.tables).intersection(target.tables)
+        for table in sharedTables.sorted() {
+            let existing = Set((target.columnsByTable[table] ?? []).map(\.name))
+            for column in source.columnsByTable[table] ?? [] where !existing.contains(column.name) {
+                // Avoid inventing defaults or generating DDL that may fail on
+                // populated tables. Require manual review of every statement.
+                var definition = "\(identifier(column.name)) \(column.dataType)"
+                definition += column.nullable ? " NULL" : " NOT NULL"
+                if column.extra.uppercased().contains("AUTO_INCREMENT") {
+                    // Auto-increment needs key/constraint context absent from the cache.
+                    continue
+                }
+                let statement = "ALTER TABLE \(identifier(targetDatabase)).\(identifier(table)) ADD COLUMN \(definition);"
+                result.append(Migration(id: "\(table).\(column.name)", label: "\(table).\(column.name)", sql: statement))
+            }
+        }
+        return result
+    }
+
+    private var selectedMigrations: [Migration] {
+        migrations.filter { selectedMigrationIDs.contains($0.id) }
+    }
+
+    private var migrationSQL: String {
+        let header = "-- DBSyn Phase 65: review carefully before execution.\n" +
+            "-- Source: \(sourceDatabase)  Target: \(targetDatabase)\n" +
+            "-- Additive columns only; no tables, views, keys or destructive changes.\n" +
+            "-- MySQL DDL implicitly commits; take a backup first.\n\n"
+        return header + selectedMigrations.map(\.sql).joined(separator: "\n")
+    }
+
     var body: some View {
         VStack(alignment: .leading, spacing: 14) {
             HStack {
@@ -6408,6 +6457,18 @@ private struct DBSynSchemaCompareView: View {
                     }
                 }
             }
+            if source != nil && target != nil {
+                HStack {
+                    Button("Review Additive Migration…") {
+                        selectedMigrationIDs = Set(migrations.map(\.id))
+                        showMigrationPreview = true
+                    }
+                    .disabled(migrations.isEmpty)
+                    Text("\(migrations.count) eligible missing columns · tables and views require full DDL")
+                        .font(.caption).foregroundStyle(.secondary)
+                    Spacer()
+                }
+            }
             Divider()
             if targetDatabase.isEmpty {
                 ContentUnavailableView("Choose a target database", systemImage: "square.on.square", description: Text("Select another schema on this connection."))
@@ -6432,5 +6493,52 @@ private struct DBSynSchemaCompareView: View {
         .onAppear {
             if targetDatabase.isEmpty { targetDatabase = model.databases.first(where: { $0 != sourceDatabase }) ?? "" }
         }
+        .sheet(isPresented: $showMigrationPreview) {
+            VStack(alignment: .leading, spacing: 12) {
+                Text("Review Additive Migration").font(.title2).bold()
+                Text("Select columns to add to \(targetDatabase). Nothing is executed automatically.")
+                    .foregroundStyle(.secondary)
+                List(migrations) { migration in
+                    Toggle(migration.label, isOn: Binding(
+                        get: { selectedMigrationIDs.contains(migration.id) },
+                        set: { enabled in
+                            if enabled { selectedMigrationIDs.insert(migration.id) }
+                            else { selectedMigrationIDs.remove(migration.id) }
+                        }
+                    ))
+                }
+                .frame(minHeight: 130)
+                Text("SQL Preview").font(.headline)
+                ScrollView {
+                    Text(migrationSQL)
+                        .font(.system(.body, design: .monospaced))
+                        .textSelection(.enabled)
+                        .frame(maxWidth: .infinity, alignment: .leading)
+                        .padding(12)
+                }
+                .background(.quaternary.opacity(0.3))
+                .frame(minHeight: 150)
+                Text("Warning: NOT NULL columns without defaults may fail on populated tables. Verify types, indexes and constraints manually. MySQL DDL may implicitly commit.")
+                    .font(.caption).foregroundStyle(.secondary)
+                HStack {
+                    Spacer()
+                    Button("Cancel") { showMigrationPreview = false }
+                    Button("Copy SQL") {
+                        NSPasteboard.general.clearContents()
+                        NSPasteboard.general.setString(migrationSQL, forType: .string)
+                    }
+                    .disabled(selectedMigrations.isEmpty)
+                    Button("Open in SQL Editor") {
+                        model.newQueryTab()
+                        model.sql = migrationSQL
+                        showMigrationPreview = false
+                        dismiss()
+                    }
+                    .disabled(selectedMigrations.isEmpty)
+                }
+            }
+            .padding(20)
+            .frame(minWidth: 750, minHeight: 560)
+        }
     }
 }