Use DateCreated as homograph tie-breaker

src/SIL.LCModel/DomainImpl/OverridesLing_Lex.cs

@@ -417,8 +417,13 @@ public static bool CorrectHomographNumbers(List<ILexEntry> rgHomographs)
 			{
 				// Should we notify the user that we're doing this helpful renumbering for him?
 				// We do our best to keep them in the same order.
+				// Tie-break on DateCreated then Guid so the result is deterministic and reasonable.
 				int n = 1;
-				foreach (ILexEntry le in rgHomographs.OrderBy(h => h.HomographNumber).ToList())
+				foreach (ILexEntry le in rgHomographs
+					.OrderBy(h => h.HomographNumber)
+					.ThenBy(h => h.DateCreated)
+					.ThenBy(h => h.Guid)
+					.ToList())
 				{
 					if (le.HomographNumber != n)
 						le.HomographNumber = n;

src/SIL.LCModel/Infrastructure/Impl/RepositoryAdditions.cs

@@ -1365,6 +1365,25 @@ public List<ILexEntry> CollectHomographs(string sForm, IMoMorphType morphType)
 			return CollectHomographs(sForm, 0, GetHomographs(sForm), morphType);
 		}
 
+		/// <summary>
+		/// Validate and, if needed, correct homograph numbers for the set <paramref name="entry"/>
+		/// participates in. Zeros the entry's HomographNumber if form is blank (so callers
+		/// don't need to special-case that).
+		/// Caller should create the unit of work.
+		/// </summary>
+		/// <returns>true if no change was needed, false if anything was renumbered.</returns>
+		public bool CorrectHomographNumbers(ILexEntry entry)
+		{
+			var form = entry.HomographFormKey;
+			if (form == Strings.ksQuestions)
+			{
+				if (entry.HomographNumber == 0) return true;
+				entry.HomographNumber = 0;
+				return false;
+			}
+			return LexDb.CorrectHomographNumbers(CollectHomographs(form, entry.PrimaryMorphType));
+		}
+
 		/// <summary>
 		/// Main method to collect all the homographs of the given form from the given list of entries.
 		/// Set hvo to 0 to collect absolutely every matching homograph.

src/SIL.LCModel/RepositoryInterfaceAdditions.cs

@@ -426,6 +426,15 @@ public partial interface ILexEntryRepository
 		/// </summary>
 		List<ILexEntry> CollectHomographs(string sForm, IMoMorphType morphType);
 
+		/// <summary>
+		/// Validate and, if needed, correct homograph numbers for the set <paramref name="entry"/>
+		/// participates in. Zeros the entry's HomographNumber if form is blank (so callers
+		/// don't need to special-case that).
+		/// Caller should create the unit of work.
+		/// </summary>
+		/// <returns>true if no change was needed, false if anything was renumbered.</returns>
+		bool CorrectHomographNumbers(ILexEntry entry);
+
 		/// <summary>
 		/// Maps the specified morph type onto a canonical ordering that should be used in comparing two
 		/// entries to see whether they are homographs.

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

@@ -267,6 +267,74 @@ public void HomographValidationWorks()
 			}
 		}
 
+		/// <summary>
+		/// When a full renumber is needed, ties on HomographNumber are broken by
+		/// DateCreated (then Guid) so that the outcome is entirely deterministic.
+		/// </summary>
+		[Test]
+		public void CorrectHomographNumbers_FullRenumber_TieBreaksByDateCreated()
+		{
+			const string sLexForm = "tieBreakTest";
+			var e1 = MakeEntry(sLexForm);
+			var e2 = MakeEntry(sLexForm);
+			var e3 = MakeEntry(sLexForm);
+
+			e1.HomographNumber = 5;
+			e2.HomographNumber = 5;
+			e3.HomographNumber = 5;
+
+			// Reverse natural creation order so DateCreated differs from insertion order.
+			var baseTime = new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+			e3.DateCreated = baseTime;
+			e2.DateCreated = baseTime.AddMinutes(1);
+			e1.DateCreated = baseTime.AddMinutes(2);
+
+			var fOk = LexDb.CorrectHomographNumbers(new List<ILexEntry> { e1, e2, e3 });
+
+			Assert.IsFalse(fOk, "CorrectHomographNumbers had to renumber homographs");
+			Assert.AreEqual(1, e3.HomographNumber, "oldest DateCreated wins HN=1");
+			Assert.AreEqual(2, e2.HomographNumber);
+			Assert.AreEqual(3, e1.HomographNumber, "newest DateCreated gets HN=3");
+		}
+
+		/// <summary>
+		/// Algorithm behaviour is covered by HomographValidationWorks.
+		/// This just exercises the wrapper.
+		/// </summary>
+		[Test]
+		public void CorrectHomographNumbers_RenumbersInvalidSet()
+		{
+			const string sLexForm = "repoCorrectHnTest";
+			var e1 = MakeEntry(sLexForm);
+			var e2 = MakeEntry(sLexForm);
+			var e3 = MakeEntry(sLexForm);
+
+			e1.HomographNumber = 2;
+			e2.HomographNumber = 2;
+			e3.HomographNumber = 0;
+
+			var repo = Cache.ServiceLocator.GetInstance<ILexEntryRepository>();
+			Assert.IsFalse(repo.CorrectHomographNumbers(e1), "Invalid set should be renumbered.");
+			CollectionAssert.AreEquivalent(new[] { 1, 2, 3 },
+				new[] { e1.HomographNumber, e2.HomographNumber, e3.HomographNumber });
+			Assert.IsTrue(repo.CorrectHomographNumbers(e1), "Already-valid set: no change.");
+		}
+
+		/// <summary>
+		/// Empty-form branch added on top of LexDb.CorrectHomographNumbers.
+		/// </summary>
+		[Test]
+		public void CorrectHomographNumbers_EmptyForm_ForcesZero()
+		{
+			var entry = MakeEntry("");
+			Assert.AreEqual(Strings.ksQuestions, entry.HomographFormKey);
+			entry.HomographNumber = 7;
+
+			var repo = Cache.ServiceLocator.GetInstance<ILexEntryRepository>();
+			Assert.IsFalse(repo.CorrectHomographNumbers(entry));
+			Assert.AreEqual(0, entry.HomographNumber);
+		}
+
 		private ILexEntry MakeEntry(string sLexForm)
 		{
 			var lme = Cache.ServiceLocator.GetInstance<ILexEntryFactory>().Create();