From e5bd3e1400d3908dcbe929fc29d1b20dc0890b13 Mon Sep 17 00:00:00 2001
From: John Maxwell <maxwellparc@gmail.com>
Date: Mon, 13 Jan 2025 09:40:02 -0800
Subject: [PATCH] Fix another bug with MorphologicalRuleOrder.Linear

---
 .../AnalysisStratumRule.cs                    |  6 +-
 .../MorpherTests.cs                           | 57 +++++++++++++++++++
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/src/SIL.Machine.Morphology.HermitCrab/AnalysisStratumRule.cs b/src/SIL.Machine.Morphology.HermitCrab/AnalysisStratumRule.cs
index 0edc7f9b..74681bc2 100644
--- a/src/SIL.Machine.Morphology.HermitCrab/AnalysisStratumRule.cs
+++ b/src/SIL.Machine.Morphology.HermitCrab/AnalysisStratumRule.cs
@@ -34,7 +34,11 @@ public AnalysisStratumRule(Morpher morpher, Stratum stratum)
             switch (stratum.MorphologicalRuleOrder)
             {
                 case MorphologicalRuleOrder.Linear:
-                    _mrulesRule = new LinearRuleCascade<Word, ShapeNode>(
+                    // Use PermutationRuleCascade instead of LinearRuleCascade
+                    // because morphological rules should be considered optional
+                    // during unapplication (they are obligatory during application,
+                    // but we don't know they have been applied during unapplication).
+                    _mrulesRule = new PermutationRuleCascade<Word, ShapeNode>(
                         mrules,
                         true,
                         FreezableEqualityComparer<Word>.Default
diff --git a/tests/SIL.Machine.Morphology.HermitCrab.Tests/MorpherTests.cs b/tests/SIL.Machine.Morphology.HermitCrab.Tests/MorpherTests.cs
index e17f09f9..d122802c 100644
--- a/tests/SIL.Machine.Morphology.HermitCrab.Tests/MorpherTests.cs
+++ b/tests/SIL.Machine.Morphology.HermitCrab.Tests/MorpherTests.cs
@@ -3,6 +3,7 @@
 using SIL.Machine.FeatureModel;
 using SIL.Machine.Matching;
 using SIL.Machine.Morphology.HermitCrab.MorphologicalRules;
+using SIL.Machine.Morphology.HermitCrab.PhonologicalRules;
 
 namespace SIL.Machine.Morphology.HermitCrab;
 
@@ -36,8 +37,64 @@ public void AnalyzeWord_CanAnalyze_ReturnsCorrectAnalysis()
             morpher.AnalyzeWord("sagd"),
             Is.EquivalentTo(new[] { new WordAnalysis(new IMorpheme[] { Entries["32"], edSuffix }, 0, "V") })
         );
+    }
+
+    [Test]
+    public void AnalyzeWord_CanAnalyzeLinear_ReturnsCorrectAnalysis()
+    {
+        var any = FeatureStruct.New().Symbol(HCFeatureSystem.Segment).Value;
+
+        var edSuffix = new AffixProcessRule
+        {
+            Id = "PAST",
+            Name = "ed_suffix",
+            Gloss = "PAST",
+            RequiredSyntacticFeatureStruct = FeatureStruct.New(Language.SyntacticFeatureSystem).Symbol("V").Value
+        };
+        edSuffix.Allomorphs.Add(
+            new AffixProcessAllomorph
+            {
+                Lhs = { Pattern<Word, ShapeNode>.New("1").Annotation(any).OneOrMore.Value },
+                Rhs = { new CopyFromInput("1"), new InsertSegments(Table3, "+d") }
+            }
+        );
+        Morphophonemic.MorphologicalRules.Add(edSuffix);
+
+        // Adding rules shouldn't block sagd analysis when Linear.
+        var tSuffix = new AffixProcessRule
+        {
+            Id = "PLURAL",
+            Name = "t_suffix",
+            Gloss = "PLURAL",
+            RequiredSyntacticFeatureStruct = FeatureStruct.New(Language.SyntacticFeatureSystem).Symbol("N").Value
+        };
+        tSuffix.Allomorphs.Add(
+            new AffixProcessAllomorph
+            {
+                Lhs = { Pattern<Word, ShapeNode>.New("1").Annotation(any).OneOrMore.Value },
+                Rhs = { new CopyFromInput("1"), new InsertSegments(Table3, "+t") }
+            }
+        );
+        Morphophonemic.MorphologicalRules.Add(tSuffix);
+
+        // Add a phonological rule so that "sagd" becomes "sag[dt]" during unapplication.
+        // This is to verify that unapplication works correctly.
+        var rule1 = new RewriteRule
+        {
+            Name = "rule1",
+            Lhs = Pattern<Word, ShapeNode>.New().Annotation(Character(Table1, "t")).Value
+        };
+        rule1.Subrules.Add(
+            new RewriteSubrule
+            {
+                Rhs = Pattern<Word, ShapeNode>.New().Annotation(Character(Table1, "d")).Value,
+            }
+        );
+        Morphophonemic.PhonologicalRules.Add(rule1);
 
         SetRuleOrder(MorphologicalRuleOrder.Linear);
+        var morpher = new Morpher(TraceManager, Language);
+
         Assert.That(
             morpher.AnalyzeWord("sagd"),
             Is.EquivalentTo(new[] { new WordAnalysis(new IMorpheme[] { Entries["32"], edSuffix }, 0, "V") })