perf(hermitcrab): keep the required-slot look-ahead testing behind slots whose unmatched parts are unbounded runs

src/SIL.Machine.Morphology.HermitCrab/RequiredSlotMaterial.cs

@@ -72,7 +72,8 @@ public static SlotWalk Start()
     /// <see cref="InsertSimpleContext.GenerateAnalysisLhs"/>), and the rule can only unapply if the constraints
     /// unify with segment nodes of the shape in that order, each node used once. A rule is pure when every
     /// right-hand side action copies an input part or inserts material, and every left-hand part is copied by a
-    /// <see cref="CopyFromInput"/> that must capture a segment, or has no segment to restore. Then
+    /// <see cref="CopyFromInput"/> that must capture a segment, or restores no segment when it captures nothing
+    /// (<see cref="AnalysisMorphologicalTransform"/> writes nothing back for an unbounded quantifier). Then
     /// <see cref="AnalysisMorphologicalTransform.GenerateShape"/> only copies input nodes and never untruncates a
     /// segment. Unification can only narrow the feature structure of a copied node, so a constraint that unifies
     /// with no node of the shape unifies with no node of the shape after any number of pure unapplications. Inside
@@ -429,6 +430,8 @@ private static bool IsPure(AffixProcessAllomorph allomorph)
             {
                 if (!HasSegmentConstraint(part))
                     continue;
+                if (RestoredSegments(part) == 0)
+                    continue;
                 if (!copied.Contains(part.Name) || MinSegments(part) == 0)
                     return false;
             }
@@ -460,6 +463,23 @@ private static bool HasSegmentConstraint(PatternNode<Word, ShapeNode> node)
             return node.Children.Any(HasSegmentConstraint);
         }
 
+        // The segment nodes that AnalysisMorphologicalTransform.Untruncate writes for a part that was not
+        // captured. An unbounded quantifier writes none, as in Mbugwe's vowel-fusion slots.
+        private static int RestoredSegments(PatternNode<Word, ShapeNode> node)
+        {
+            int total = 0;
+            foreach (PatternNode<Word, ShapeNode> child in node.Children)
+            {
+                if (child is Constraint<Word, ShapeNode> constraint && constraint.Type() == HCFeatureSystem.Segment)
+                    total++;
+                else if (child is Quantifier<Word, ShapeNode> quantifier)
+                    total += Math.Max(0, quantifier.MaxOccur) * RestoredSegments(quantifier);
+                else
+                    total += RestoredSegments(child);
+            }
+            return total;
+        }
+
         // The fewest segments a successful match of the node must consume. A part matching none is captured
         // as a null range, and GenerateShape then untruncates it, which adds segments that are not copies.
         private static int MinSegments(PatternNode<Word, ShapeNode> node)

tests/SIL.Machine.Morphology.HermitCrab.Tests/AnalysisAffixTemplateFusionTests.cs

@@ -0,0 +1,238 @@
+using NUnit.Framework;
+using SIL.Machine.Annotations;
+using SIL.Machine.FeatureModel;
+using SIL.Machine.Matching;
+using SIL.Machine.Morphology.HermitCrab.MorphologicalRules;
+
+namespace SIL.Machine.Morphology.HermitCrab;
+
+// A vowel-fusion slot copies a part that may match nothing; the look-ahead may test behind it only if it
+// restores no segment. Slots are in synthesis order and unapplied last to first.
+[TestFixture]
+public class AnalysisAffixTemplateFusionTests : HermitCrabTestBase
+{
+    private static readonly FeatureStruct Any = FeatureStruct.New().Symbol(HCFeatureSystem.Segment).Value;
+
+    private sealed record WalkResult(List<string> Parses, int RuleAttempts, int Violations);
+
+    private static AffixTemplateSlot Slot(bool optional, params MorphemicMorphologicalRule[] rules) =>
+        new(rules) { Optional = optional };
+
+    private static AffixTemplate TemplateOf(params AffixTemplateSlot[] slots)
+    {
+        var template = new AffixTemplate { Name = "fusion_template" };
+        foreach (AffixTemplateSlot slot in slots)
+            template.Slots.Add(slot);
+        return template;
+    }
+
+    private static AffixProcessRule RuleOf(
+        string name,
+        Pattern<Word, ShapeNode>[] lhs,
+        params MorphologicalOutputAction[] rhs
+    )
+    {
+        var rule = new AffixProcessRule
+        {
+            Id = name,
+            Name = name,
+            Gloss = name,
+            RequiredSyntacticFeatureStruct = FeatureStruct.New().Value,
+            OutSyntacticFeatureStruct = FeatureStruct.New().Value,
+        };
+        var allomorph = new AffixProcessAllomorph();
+        foreach (Pattern<Word, ShapeNode> part in lhs)
+            allomorph.Lhs.Add(part);
+        foreach (MorphologicalOutputAction action in rhs)
+            allomorph.Rhs.Add(action);
+        rule.Allomorphs.Add(allomorph);
+        return rule;
+    }
+
+    private AffixProcessRule Suffix(string insert) =>
+        RuleOf(
+            "suffix_" + insert,
+            new[] { Pattern<Word, ShapeNode>.New("1").Annotation(Any).OneOrMore.Value },
+            new CopyFromInput("1"),
+            new InsertSegments(Table3, insert)
+        );
+
+    // Like Mbugwe's object markers: a prefix whose stem vowel is copied twice, followed by an unbounded run
+    // that may be empty.
+    private AffixProcessRule FusionPrefix(string name, string before, string between) =>
+        RuleOf(
+            name,
+            new[]
+            {
+                Pattern<Word, ShapeNode>.New("1").Annotation(Any).Value,
+                Pattern<Word, ShapeNode>.New("2").Annotation(Any).ZeroOrMore.Value,
+            },
+            new InsertSegments(Table3, before),
+            new CopyFromInput("1"),
+            new InsertSegments(Table3, between),
+            new CopyFromInput("1"),
+            new CopyFromInput("2")
+        );
+
+    // The run is capped at one segment, so an unmatched run is written back as an optional segment.
+    private AffixProcessRule BoundedRunSuffix(string insert) =>
+        RuleOf(
+            "bounded_" + insert,
+            new[]
+            {
+                Pattern<Word, ShapeNode>.New("1").Annotation(Any).OneOrMore.Value,
+                Pattern<Word, ShapeNode>.New("2").Annotation(Any).Optional.Value,
+            },
+            new CopyFromInput("1"),
+            new InsertSegments(Table3, insert)
+        );
+
+    private WalkResult Walk(
+        AffixTemplate template,
+        string form,
+        RequiredSlotLookaheadMode mode,
+        int maxDegreeOfParallelism = 1
+    )
+    {
+        int attempts = 0;
+        int violations = 0;
+        var morpher = new Morpher(TraceManager, Language, maxDegreeOfParallelism)
+        {
+            RequiredSlotLookahead = mode,
+            RuleSelector = rule =>
+            {
+                if (rule is AffixProcessRule)
+                    System.Threading.Interlocked.Increment(ref attempts);
+                return true;
+            },
+            RequiredSlotShadow = (kind, t, slot) =>
+            {
+                if (kind != "fired")
+                    System.Threading.Interlocked.Increment(ref violations);
+            },
+        };
+        TraceManager.IsTracing = false;
+        var input = new Word(Morphophonemic, Morphophonemic.CharacterDefinitionTable.Segment(form));
+        input.Freeze();
+        List<string> parses = template
+            .CompileAnalysisRule(morpher)
+            .Apply(input)
+            .Select(w => w.ToString() + " " + string.Join(",", w.AllomorphsInMorphOrder.Select(a => a.Morpheme.Gloss)))
+            .OrderBy(p => p, System.StringComparer.Ordinal)
+            .ToList();
+        return new WalkResult(parses, attempts, violations);
+    }
+
+    private (WalkResult Off, WalkResult On) WalkBoth(AffixTemplate template, string form)
+    {
+        WalkResult off = Walk(template, form, RequiredSlotLookaheadMode.Off);
+        WalkResult on = Walk(template, form, RequiredSlotLookaheadMode.On);
+        Assert.That(on.Parses, Is.EqualTo(off.Parses), "the look-ahead must not change the parses of " + form);
+        return (off, on);
+    }
+
+    [Test]
+    public void Apply_FusionSlotWithAnUnboundedRun_StillTestsTheRequiredSlotBehindIt()
+    {
+        // -ti is required inside the fusion prefix and "sagu" has no t
+        AffixTemplate template = TemplateOf(Slot(false, Suffix("ti")), Slot(true, FusionPrefix("fuse", "k", "a")));
+
+        (WalkResult off, WalkResult on) = WalkBoth(template, "sagu");
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(off.Parses, Is.Empty);
+            Assert.That(off.RuleAttempts, Is.GreaterThan(0));
+            Assert.That(on.RuleAttempts, Is.EqualTo(0), "the fusion slot restores nothing, so -ti cannot appear");
+        });
+    }
+
+    [Test]
+    public void Apply_FusionSlotWithAnUnboundedRun_KeepsAWordThatHasTheMaterial()
+    {
+        AffixTemplate template = TemplateOf(Slot(false, Suffix("ti")), Slot(true, FusionPrefix("fuse", "k", "a")));
+
+        foreach (string form in new[] { "kasagti", "ksagti", "sagti", "kasagtiz" })
+        {
+            (WalkResult off, WalkResult on) = WalkBoth(template, form);
+            Assert.That(on.RuleAttempts, Is.EqualTo(off.RuleAttempts), form);
+        }
+    }
+
+    [Test]
+    public void Apply_SlotWithABoundedRunThatMayBeEmpty_RestoresASegmentTheInnerSlotCanUse()
+    {
+        // the run is written back as an optional segment, which can stand for the i of -ti
+        AffixTemplate template = TemplateOf(Slot(false, Suffix("ti")), Slot(true, BoundedRunSuffix("z")));
+
+        (WalkResult off, WalkResult on) = WalkBoth(template, "sagtz");
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(on.Parses, Is.Not.Empty, "the parse that needs the restored segment must survive");
+            Assert.That(on.RuleAttempts, Is.EqualTo(off.RuleAttempts));
+        });
+    }
+
+    [Test]
+    public void Apply_SlotWithABoundedRunThatMayBeEmpty_StaysImpureWhenTheMaterialIsAbsent()
+    {
+        AffixTemplate template = TemplateOf(Slot(false, Suffix("ti")), Slot(true, BoundedRunSuffix("z")));
+
+        (WalkResult off, WalkResult on) = WalkBoth(template, "sagz");
+
+        Assert.That(on.RuleAttempts, Is.GreaterThan(0), "the slot may restore up to one segment, so no pruning");
+    }
+
+    [TestCase(1)]
+    [TestCase(0)]
+    public void Apply_OnEveryFusionTemplateAndWord_KeepsTheParsesAndNeverViolatesTheShadow(int maxDegreeOfParallelism)
+    {
+        var templates = new Dictionary<AffixTemplate, string[]>
+        {
+            [TemplateOf(Slot(false, Suffix("ti")), Slot(true, FusionPrefix("fuse", "k", "a")))] = new[]
+            {
+                "kasagti",
+                "ksagti",
+                "sagu",
+                "sagti",
+            },
+            [
+                TemplateOf(
+                    Slot(false, Suffix("ti")),
+                    Slot(false, FusionPrefix("fuse", "k", "a")),
+                    Slot(true, Suffix("z"))
+                )
+            ] = new[] { "kasagtiz", "kasagtzi", "kasagz" },
+            [TemplateOf(Slot(false, Suffix("ti")), Slot(true, BoundedRunSuffix("z")))] = new[]
+            {
+                "sagtz",
+                "sagz",
+                "sagtiz",
+            },
+            [
+                TemplateOf(
+                    Slot(false, Suffix("u")),
+                    Slot(false, FusionPrefix("fuse", "k", "a")),
+                    Slot(false, Suffix("ti"))
+                )
+            ] = new[] { "kasagtiu", "kasaguti", "sagtiu" },
+        };
+
+        foreach ((AffixTemplate template, string[] forms) in templates)
+        {
+            foreach (string form in forms)
+            {
+                WalkResult off = Walk(template, form, RequiredSlotLookaheadMode.Off, maxDegreeOfParallelism);
+                WalkResult on = Walk(template, form, RequiredSlotLookaheadMode.On, maxDegreeOfParallelism);
+                WalkResult shadow = Walk(template, form, RequiredSlotLookaheadMode.Shadow, maxDegreeOfParallelism);
+                Assert.Multiple(() =>
+                {
+                    Assert.That(on.Parses, Is.EqualTo(off.Parses), form);
+                    Assert.That(shadow.Parses, Is.EqualTo(off.Parses), form);
+                    Assert.That(shadow.Violations, Is.EqualTo(0), form);
+                });
+            }
+        }
+    }
+}

tests/SIL.Machine.Morphology.HermitCrab.Tests/AnalysisAffixTemplateRuleTests.cs

@@ -307,10 +307,10 @@ MorphologicalOutputAction[] rhs
     }
 
     [Test]
-    public void Apply_CopiedPartThatMayMatchNothing_MakesTheSlotImpure()
+    public void Apply_CopiedPartCappedAtOneThatMayMatchNothing_MakesTheSlotImpure()
     {
         (WalkResult off, WalkResult on) = WalkWithOptionalSlot(
-            new[] { Pattern<Word, ShapeNode>.New("1").Annotation(Any).ZeroOrMore.Value },
+            new[] { Pattern<Word, ShapeNode>.New("1").Annotation(Any).Optional.Value },
             new MorphologicalOutputAction[] { new CopyFromInput("1") }
         );