Allow functions for testing and repair in DB integrity checks

This can be used for things that can't be checked or repaired with SQL
alone, or that are too difficult to do that way.

chrome/content/zotero/xpcom/schema.js

@@ -1195,8 +1195,11 @@ Zotero.Schema = new function(){
 		
 		// Non-foreign key checks
 		//
-		// Repair entry (second position) can be either a string or an array with multiple statements.
+		// The first position is for testing and the second is for repairing. Can be either SQL
-		var queries = [
+		// statements or promise-returning functions. For statements, the repair entry can be either a
+		// string or an array with multiple statements. Functions should avoid assuming any global state
+		// (e.g., loaded data).
+		var checks = [
 			// Can't be a FK with itemTypesCombined
 			[
 				"SELECT COUNT(*) > 1 FROM items WHERE itemTypeID IS NULL",
@@ -1246,8 +1249,16 @@ Zotero.Schema = new function(){
 			]
 		];
 		
-		for (let sql of queries) {
+		for (let check of checks) {
-			let errorsFound = yield Zotero.DB.valueQueryAsync(sql[0]);
+			let errorsFound = false;
+			// SQL statement
+			if (typeof check[0] == 'string') {
+				errorsFound = yield Zotero.DB.valueQueryAsync(check[0]);
+			}
+			// Function
+			else {
+				errorsFound = yield check[0]();
+			}
 			if (!errorsFound) {
 				continue;
 			}
@@ -1257,15 +1268,19 @@ Zotero.Schema = new function(){
 			if (fix) {
 				try {
 					// Single query
-					if (typeof sql[1] == 'string') {
+					if (typeof check[1] == 'string') {
-						yield Zotero.DB.queryAsync(sql[1]);
+						yield Zotero.DB.queryAsync(check[1]);
 					}
 					// Multiple queries
-					else {
+					else if (Array.isArray(check[1])) {
-						for (let s of sql[1]) {
+						for (let s of check[1]) {
 							yield Zotero.DB.queryAsync(s);
 						}
 					}
+					// Function
+					else {
+						yield check[1]();
+					}
 					continue;
 				}
 				catch (e) {