[LL] support search for decompiled fir for type parameters

^ KTIJ-25976

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/util/FirDeclarationForCompiledElementSearcher.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.analysis.low.level.api.fir.util
 
+import org.jetbrains.kotlin.analysis.low.level.api.fir.element.builder.containingDeclaration
 import org.jetbrains.kotlin.analysis.low.level.api.fir.project.structure.llFirModuleData
 import org.jetbrains.kotlin.analysis.low.level.api.fir.providers.LLFirModuleWithDependenciesSymbolProvider
 import org.jetbrains.kotlin.analysis.low.level.api.fir.sessions.LLFirBuiltinsAndCloneableSession
@@ -40,11 +41,23 @@ internal class FirDeclarationForCompiledElementSearcher(private val symbolProvid
             is KtProperty -> findNonLocalProperty(ktDeclaration)
             is KtParameter -> findParameter(ktDeclaration)
             is KtPropertyAccessor -> findNonLocalPropertyAccessor(ktDeclaration)
+            is KtTypeParameter -> findNonLocalTypeParameter(ktDeclaration)
 
             else -> errorWithFirSpecificEntries("Unsupported compiled declaration of type", psi = ktDeclaration)
         }
     }
 
+    private fun findNonLocalTypeParameter(param: KtTypeParameter): FirDeclaration {
+        val owner = param.containingDeclaration ?: errorWithFirSpecificEntries("Unsupported compiled type parameter", psi = param)
+        val firDeclaration = findNonLocalDeclaration(owner)
+        val firTypeParameterRefOwner = firDeclaration as? FirTypeParameterRefsOwner ?: errorWithFirSpecificEntries(
+            "No fir found by $owner",
+            psi = owner,
+            fir = firDeclaration
+        )
+        return firTypeParameterRefOwner.typeParameters.find { it.realPsi === param } as FirDeclaration
+    }
+
     private fun findParameter(param: KtParameter): FirDeclaration {
         val ownerFunction = param.ownerFunction ?: errorWithFirSpecificEntries("Unsupported compiled parameter", psi = param)
         val firDeclaration = findNonLocalDeclaration(ownerFunction)
@@ -53,7 +66,7 @@ internal class FirDeclarationForCompiledElementSearcher(private val symbolProvid
             psi = ownerFunction,
             fir = firDeclaration
         )
-        return firFunction.valueParameters.find { it.name == param.nameAsSafeName }
+        return firFunction.valueParameters.find { it.realPsi === param }
             ?: errorWithFirSpecificEntries("No fir value parameter found", psi = param, fir = firFunction)
     }
 
@@ -66,7 +79,7 @@ internal class FirDeclarationForCompiledElementSearcher(private val symbolProvid
             ?: errorWithFirSpecificEntries("We should be able to find a symbol for $classId", psi = declaration)
 
         return (classCandidate.fir as? FirRegularClass)?.declarations?.first {
-            it is FirEnumEntry && it.name == declaration.nameAsName
+            it is FirEnumEntry && it.realPsi === declaration
         } as FirEnumEntry
     }
 
@@ -107,7 +120,7 @@ internal class FirDeclarationForCompiledElementSearcher(private val symbolProvid
 
         val constructorCandidate =
             symbolProvider.getClassDeclaredConstructors(classId)
-                .singleOrNull { representSameConstructor(declaration, it.fir) }
+                .singleOrNull { it.fir.realPsi === declaration }
                 ?: errorWithFirSpecificEntries("We should be able to find a constructor", psi = declaration)
 
         return constructorCandidate.fir
@@ -192,14 +205,6 @@ private fun FirSymbolProvider.findCallableCandidates(
             getClassDeclaredPropertySymbols(containerClassId, shortName)
 }
 
-private fun representSameConstructor(psiConstructor: KtConstructor<*>, firConstructor: FirConstructor): Boolean {
-    if ((firConstructor.isPrimary) != (psiConstructor is KtPrimaryConstructor)) {
-        return false
-    }
-
-    return firConstructor.realPsi === psiConstructor
-}
-
 private fun ExceptionAttachmentBuilder.withCandidates(candidates: List<FirBasedSymbol<*>>) {
     withEntry("Candidates count", candidates.size.toString())
     for ((index, candidate) in candidates.withIndex()) {

analysis/low-level-api-fir/testdata/getOrBuildFirBinary/typeParameter.kt

@@ -0,0 +1,4 @@
+// DECLARATION_TYPE: org.jetbrains.kotlin.psi.KtTypeParameter
+class FooBar<T> {
+    fun doSmth(t: T) {}
+}

analysis/low-level-api-fir/testdata/getOrBuildFirBinary/typeParameter.txt

@@ -0,0 +1,8 @@
+KT element: KtTypeParameter
+KT element text:
+T
+FIR element: FirTypeParameterImpl
+FIR source kind: KtRealSourceElementKind
+
+FIR element rendered:
+[ResolvedTo(BODY_RESOLVE)] T

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/AbstractLibraryGetOrBuildFirTest.kt

@@ -63,6 +63,9 @@ abstract class AbstractLibraryGetOrBuildFirTest : AbstractLowLevelApiSingleFileT
             if (decl is KtProperty) {
                 findFirstDeclaration(decl.accessors, expectedClass)?.let { return it }
             }
+            if (decl is KtTypeParameterListOwner) {
+                findFirstDeclaration(decl.typeParameters, expectedClass)?.let { return it }
+            }
             if (decl is KtClass && KtConstructor::class.java.isAssignableFrom(expectedClass)) {
                 decl.primaryConstructor?.let { return it }
             }

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/LibraryGetOrBuildFirTestGenerated.java

@@ -78,6 +78,12 @@ public class LibraryGetOrBuildFirTestGenerated extends AbstractLibraryGetOrBuild
         runTest("analysis/low-level-api-fir/testdata/getOrBuildFirBinary/topLevelFunction.kt");
     }
 
+    @Test
+    @TestMetadata("typeParameter.kt")
+    public void testTypeParameter() throws Exception {
+        runTest("analysis/low-level-api-fir/testdata/getOrBuildFirBinary/typeParameter.kt");
+    }
+
     @Nested
     @TestMetadata("analysis/low-level-api-fir/testdata/getOrBuildFirBinary/publishedApi")
     @TestDataPath("$PROJECT_ROOT")