ADFA-3730 | Make K2 completion fuzzy-match consistent with Java (#1483)

* ADFA-3730 | Make K2 completion fuzzy-match inclusive, matching Java

Switch K2 scope/member/extension candidate inclusion from prefix-only to
matchLevel != NO_MATCH so fuzzy matches appear, matching the Java LSP.
Route every match-level computation through a per-request memo cache on
AnalysisContext so CompletionItem.matchLevel runs once per candidate name.

* ADFA-3730 | Compute match level once per candidate in Java scope completion

ScopeCompletionProvider computed matchLevel twice per candidate — once in
the filter predicate and again when building the item. Cache the predicate's
result and reuse it in the loop, matching the sibling completion providers.

Author: itsaky-adfa

lsp/java/src/main/java/com/itsaky/androidide/lsp/java/providers/completion/ScopeCompletionProvider.kt

@@ -66,6 +66,7 @@ class ScopeCompletionProvider(
     val trees = Trees.instance(task.task)
     val list: MutableList<CompletionItem> = ArrayList()
     val scope = trees.getScope(path)
+    val matchLevels = HashMap<String, MatchLevel>()
     val filter =
       Predicate<CharSequence?> {
         if (it == null || it.isEmpty()) {
@@ -77,7 +78,9 @@ class ScopeCompletionProvider(
           name = it.substring(0, it.lastIndexOf('('))
         }
 
-        return@Predicate matchLevel(name, partial) != NO_MATCH
+        val level = matchLevel(name, partial)
+        matchLevels[name.toString()] = level
+        return@Predicate level != NO_MATCH
       }
 
     abortCompletionIfCancelled()
@@ -87,7 +90,7 @@ class ScopeCompletionProvider(
         name = name.substring(0, name.lastIndexOf('('))
       }
 
-      val matchLevel = matchLevel(name, partial)
+      val matchLevel = matchLevels.getOrDefault(name, NO_MATCH)
 
       if (member.kind == METHOD) {
         val method = member as ExecutableElement

lsp/kotlin/src/main/java/com/itsaky/androidide/lsp/kotlin/completion/KotlinCompletions.kt

@@ -17,6 +17,7 @@ import com.itsaky.androidide.lsp.models.CompletionItemKind
 import com.itsaky.androidide.lsp.models.CompletionParams
 import com.itsaky.androidide.lsp.models.CompletionResult
 import com.itsaky.androidide.lsp.models.InsertTextFormat
+import com.itsaky.androidide.lsp.models.MatchLevel
 import com.itsaky.androidide.preferences.utils.indentationString
 import com.itsaky.androidide.progress.ICancelChecker
 import com.itsaky.androidide.progress.ProgressManager
@@ -241,11 +242,11 @@ private fun KaSession.collectMembersFromType(
 	val typeScope = receiverType.scope
 	if (typeScope != null) {
 		val callables =
-			typeScope.getCallableSignatures { name -> matchesPrefix(name) }
+			typeScope.getCallableSignatures { name -> matchesFilter(name) }
 				.map { it.symbol }
 
 		val classifiers =
-			typeScope.getClassifierSymbols { name -> matchesPrefix(name) }
+			typeScope.getClassifierSymbols { name -> matchesFilter(name) }
 
 		to += toCompletionItems(callables)
 		to += toCompletionItems(classifiers)
@@ -257,8 +258,8 @@ private fun KaSession.collectMembersFromType(
 	val classSymbol = classType.symbol as? KaClassSymbol ?: return
 	val memberScope = classSymbol.memberScope
 
-	val callables = memberScope.callables { name -> matchesPrefix(name) }
-	val classifiers = memberScope.classifiers { name -> matchesPrefix(name) }
+	val callables = memberScope.callables { name -> matchesFilter(name) }
+	val classifiers = memberScope.classifiers { name -> matchesFilter(name) }
 
 	to += toCompletionItems(callables)
 	to += toCompletionItems(classifiers)
@@ -270,7 +271,7 @@ private fun KaSession.collectExtensionFunctions(
 	to: MutableList<CompletionItem>
 ) {
 	val extensionSymbols =
-		ctx.scope.callables { name -> matchesPrefix(name) }
+		ctx.scope.callables { name -> matchesFilter(name) }
 			.filter { symbol ->
 				if (!symbol.isExtension) return@filter false
 
@@ -303,7 +304,7 @@ private fun KaSession.collectScopeCompletions(
 	)
 
 	val callables =
-		scope.callables { name -> matchesPrefix(name) }
+		scope.callables { name -> matchesFilter(name) }
 			.filter { symbol ->
 
 				abortIfCancelled()
@@ -318,7 +319,7 @@ private fun KaSession.collectScopeCompletions(
 				}
 			}
 
-	val classifiers = scope.classifiers { name -> matchesPrefix(name) }
+	val classifiers = scope.classifiers { name -> matchesFilter(name) }
 
 	to += toCompletionItems(callables)
 	to += toCompletionItems(classifiers)
@@ -685,7 +686,7 @@ private fun KaSession.ktCompletionItem(
 	val item = KotlinCompletionItem()
 	item.ideLabel = name
 	item.completionKind = kind
-	item.matchLevel = CompletionItem.matchLevel(item.ideLabel, ctx.partial)
+	item.matchLevel = matchLevelFor(name)
 
 	return item
 }
@@ -754,11 +755,28 @@ private fun partialIdentifier(prefix: String): String {
 	return prefix.takeLastWhile { char -> Character.isJavaIdentifierPart(char) }
 }
 
+/**
+ * Returns the [MatchLevel] of [name] against [partial], memoized in [cache].
+ *
+ * Match level depends only on (name, partial), so memoizing by name is safe even
+ * when multiple symbols share a name. This is the single place match level is
+ * computed for a completion request; both the inclusion predicate and item
+ * creation route through it so [CompletionItem.matchLevel] runs at most once per
+ * distinct candidate name.
+ */
+internal fun memoizedMatchLevel(
+	cache: MutableMap<String, MatchLevel>,
+	name: String,
+	partial: String,
+): MatchLevel = cache.getOrPut(name) { CompletionItem.matchLevel(name, partial) }
+
 context(ctx: AnalysisContext)
-private fun matchesPrefix(name: Name): Boolean {
-	if (ctx.partial.isEmpty()) return true
-	return name.asString().startsWith(ctx.partial, ignoreCase = true)
-}
+private fun matchLevelFor(name: String): MatchLevel =
+	memoizedMatchLevel(ctx.matchLevelCache, name, ctx.partial)
+
+context(ctx: AnalysisContext)
+private fun matchesFilter(name: Name): Boolean =
+	matchLevelFor(name.asString()) != MatchLevel.NO_MATCH
 
 private fun determineCompletionContext(element: PsiElement): CompletionContext {
 	// Walk up to find a qualified expression where we're the selector

lsp/kotlin/src/main/java/com/itsaky/androidide/lsp/kotlin/utils/ContextResolver.kt

@@ -3,6 +3,7 @@ package com.itsaky.androidide.lsp.kotlin.utils
 import com.itsaky.androidide.lsp.kotlin.compiler.CompilationEnvironment
 import com.itsaky.androidide.lsp.kotlin.completion.DeclarationContext
 import com.itsaky.androidide.lsp.kotlin.completion.DeclarationKind
+import com.itsaky.androidide.lsp.models.MatchLevel
 import org.jetbrains.kotlin.analysis.api.KaSession
 import org.jetbrains.kotlin.analysis.api.components.KaScopeContext
 import org.jetbrains.kotlin.analysis.api.scopes.KaScope
@@ -45,7 +46,10 @@ internal data class AnalysisContext(
 	val existingModifiers: Set<KtModifierKeywordToken>,
 	val isInsideModifierList: Boolean,
 	val partial: String,
-)
+) {
+	/** Per-request memo of match level by candidate name. Not part of data-class identity. */
+	val matchLevelCache: MutableMap<String, MatchLevel> = HashMap()
+}
 
 /**
  * Resolves [AnalysisContext] at the given offset in the given [KtFile].

lsp/kotlin/src/test/java/com/itsaky/androidide/lsp/kotlin/completion/MatchLevelMemoTest.kt

@@ -0,0 +1,41 @@
+package com.itsaky.androidide.lsp.kotlin.completion
+
+import com.google.common.truth.Truth.assertThat
+import com.itsaky.androidide.lsp.models.MatchLevel
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+@RunWith(JUnit4::class)
+class MatchLevelMemoTest {
+
+	@Test
+	fun `includes fuzzy non-prefix matches`() {
+		// "toStirng" is a transposition of "toString" — not a prefix, but a
+		// high fuzzy ratio (> 59), so Java admits it and K2 must too.
+		val level = memoizedMatchLevel(HashMap(), name = "toString", partial = "toStirng")
+		assertThat(level).isEqualTo(MatchLevel.PARTIAL_MATCH)
+	}
+
+	@Test
+	fun `keeps prefix matches in their tier`() {
+		val level = memoizedMatchLevel(HashMap(), name = "toString", partial = "toS")
+		assertThat(level).isEqualTo(MatchLevel.CASE_SENSITIVE_PREFIX)
+	}
+
+	@Test
+	fun `excludes candidates below the fuzzy threshold`() {
+		val level = memoizedMatchLevel(HashMap(), name = "toString", partial = "xyzw")
+		assertThat(level).isEqualTo(MatchLevel.NO_MATCH)
+	}
+
+	@Test
+	fun `computes match level once per name and reuses the cache`() {
+		// Pre-seed a deliberately wrong value. A recompute would return
+		// CASE_SENSITIVE_EQUAL; getting NO_MATCH back proves the cache was reused.
+		val cache = HashMap<String, MatchLevel>().apply { put("toString", MatchLevel.NO_MATCH) }
+		val level = memoizedMatchLevel(cache, name = "toString", partial = "toString")
+		assertThat(level).isEqualTo(MatchLevel.NO_MATCH)
+		assertThat(cache).hasSize(1)
+	}
+}