Fix LT-22834: keep multi-string alternatives in writing systems not yet known to the cache

CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
+- [SIL.LCModel] Multi-string (AUni) alternatives in writing systems the cache has not seen yet are no longer dropped on load; the writing system is created on demand, as for string runs, so the result no longer depends on activation order (LT-22834)
 - [SIL.LCModel] BaseStyleInfo now loads default font features (ktptFontVariations) from style rules, fixing font features set as style defaults being dropped on reload (LT-22351)
 - [SIL.LCModel] BaseStyleInfo no longer clobbers ws-specific font overrides inherited from a based-on style with the default font info's merely-inherited values; only explicitly-set default properties are propagated to ws overrides (LT-22351)
 - [SIL.LCModel] BulletInfo now decodes all properties of an encoded bullet font info instead of stopping at the first string property, fixing bullet font features (ktptFontVariations) being lost when a bullet font name was also set (LT-22351)

src/SIL.LCModel/DomainImpl/Strings.cs

@@ -929,10 +929,21 @@ internal static int ReadMultiUnicodeAlternative(XElement aUniNode, ILgWritingSys
 			var wsVal = aUniNode.Attribute("ws");
 			if (wsVal == null || String.IsNullOrEmpty(wsVal.Value))
 				return 0;
-			var wsHvo = wsf.GetWsFromStr(wsVal.Value);
+			// Like the runs of an AStr (see TsStringSerializer.GetWsForId), create the writing
+			// system on demand: GetWsFromStr returns 0 for one the cache has not seen yet, which
+			// dropped the alternative and made the result depend on activation order (LT-22834).
+			int wsHvo;
+			try
+			{
+				wsHvo = wsf.get_Engine(wsVal.Value).Handle;
+			}
+			catch (Exception)
+			{
+				// An identifier that cannot be made into a writing system is still dropped.
+				wsHvo = 0;
+			}
 			// Throwing out a string without a ws is probably better than crashing
 			// and preventing a db from being opened.
-			// This code currently accepts this data, only storing en__IPA and fr strings.
 			// <Form>
 			// <AUni ws="en" />
 			// <AUni ws="en__IPA">problematic</AUni>

tests/SIL.LCModel.Tests/DomainImpl/StringsTests.cs

@@ -286,6 +286,27 @@ public void AppendAlternativesTest()
 			Assert.AreEqual("Saltillo Mejico", Cache.LangProject.FieldWorkLocation.get_String(spanish.Handle).Text);
 		}
 
+		/// <summary>
+		/// LT-22834: an AUni alternative in a writing system the cache has not seen yet must be
+		/// kept (created on demand, as AStr runs are), not dropped.
+		/// </summary>
+		[Test]
+		public void ReadMultiUnicodeAlternative_UnknownWritingSystem_IsKept()
+		{
+			const string wsId = "qaa-x-lt22834";
+			var wsManager = Cache.ServiceLocator.WritingSystemManager;
+			Assert.AreEqual(0, wsManager.GetWsFromStr(wsId), "precondition: ws must be unknown");
+			var node = System.Xml.Linq.XElement.Parse("<AUni ws=\"" + wsId + "\">kept</AUni>");
+
+			ITsString tss;
+			var ws = MultiUnicodeAccessor.ReadMultiUnicodeAlternative(node, Cache.WritingSystemFactory, out tss);
+
+			Assert.AreNotEqual(0, ws, "alternative in an unknown writing system was dropped");
+			Assert.AreEqual(ws, wsManager.GetWsFromStr(wsId));
+			Assert.AreEqual("kept", tss.Text);
+			Assert.AreEqual(ws, tss.get_WritingSystemAt(0));
+		}
+
 		[Test]
 		public void ToXml_WorksAsExpected()
 		{