IDE FIR: fix resolving vararg parameter type

For a vararg parameter type, there corresponding FIR element has a fake
source of kind ArrayTypeFromVarargParameter. As a result,
`getOrBuildFir` returns the whole `FirValueParameter` for the parameter
type reference. Therefore, we need some special handling for this case
in order to resolve the proper `KtSymbol`.

idea/idea-fir/tests/org/jetbrains/kotlin/idea/resolve/FirReferenceResolveTestGenerated.java

@@ -219,6 +219,11 @@ public class FirReferenceResolveTestGenerated extends AbstractFirReferenceResolv
         runTest("idea/testData/resolve/references/InMethodParameter.kt");
     }
 
+    @TestMetadata("InMethodVarargParameter.kt")
+    public void testInMethodVarargParameter() throws Exception {
+        runTest("idea/testData/resolve/references/InMethodVarargParameter.kt");
+    }
+
     @TestMetadata("InObjectClassObject.kt")
     public void testInObjectClassObject() throws Exception {
         runTest("idea/testData/resolve/references/InObjectClassObject.kt");
@@ -229,6 +234,16 @@ public class FirReferenceResolveTestGenerated extends AbstractFirReferenceResolv
         runTest("idea/testData/resolve/references/InSecondClassObject.kt");
     }
 
+    @TestMetadata("InVaragReferenceInFunctionBody.kt")
+    public void testInVaragReferenceInFunctionBody() throws Exception {
+        runTest("idea/testData/resolve/references/InVaragReferenceInFunctionBody.kt");
+    }
+
+    @TestMetadata("InVaragReferenceInNamedParameter.kt")
+    public void testInVaragReferenceInNamedParameter() throws Exception {
+        runTest("idea/testData/resolve/references/InVaragReferenceInNamedParameter.kt");
+    }
+
     @TestMetadata("JavaAnnotationParameter.kt")
     public void testJavaAnnotationParameter() throws Exception {
         runTest("idea/testData/resolve/references/JavaAnnotationParameter.kt");

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/references/FirReferenceResolveHelper.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.idea.references
 
 import com.intellij.psi.tree.TokenSet
+import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.ROOT_PREFIX_FOR_IDE_RESOLUTION_MODE
 import org.jetbrains.kotlin.fir.declarations.*
@@ -22,10 +23,7 @@ import org.jetbrains.kotlin.fir.resolve.symbolProvider
 import org.jetbrains.kotlin.fir.resolve.toSymbol
 import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.ConeClassLikeLookupTagImpl
-import org.jetbrains.kotlin.fir.types.ConeLookupTagBasedType
-import org.jetbrains.kotlin.fir.types.FirErrorTypeRef
-import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
-import org.jetbrains.kotlin.fir.types.classId
+import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.idea.fir.getCandidateSymbols
 import org.jetbrains.kotlin.idea.fir.isImplicitFunctionCall
 import org.jetbrains.kotlin.idea.fir.low.level.api.api.getOrBuildFir
@@ -47,7 +45,7 @@ import org.jetbrains.kotlin.utils.addToStdlib.firstNotNullResult
 internal object FirReferenceResolveHelper {
     fun FirResolvedTypeRef.toTargetSymbol(session: FirSession, symbolBuilder: KtSymbolByFirBuilder): KtSymbol? {
 
-        val type = type as? ConeLookupTagBasedType
+        val type = getDeclaredType() as? ConeLookupTagBasedType
         val resolvedSymbol = type?.lookupTag?.toSymbol(session) as? AbstractFirBasedSymbol<*>
 
         val symbol = resolvedSymbol ?: run {
@@ -58,6 +56,10 @@ internal object FirReferenceResolveHelper {
         return symbol?.fir?.buildSymbol(symbolBuilder)
     }
 
+    private fun FirResolvedTypeRef.getDeclaredType() =
+        if (this.delegatedTypeRef?.source?.kind == FirFakeSourceElementKind.ArrayTypeFromVarargParameter) type.arrayElementType()
+        else type
+
     private fun ClassId.toTargetPsi(
         session: FirSession,
         symbolBuilder: KtSymbolByFirBuilder,

idea/testData/resolve/references/InMethodVarargParameter.kt

@@ -0,0 +1,9 @@
+package test
+
+class A
+
+class Test {
+    fun some(vararg a: <caret>A) = 12
+}
+
+// REF: (test).A

idea/testData/resolve/references/InVaragReferenceInFunctionBody.kt

@@ -0,0 +1,9 @@
+package test
+
+class A
+
+class Test {
+    fun some(vararg a: A) = <caret>a
+}
+
+// REF: a

idea/testData/resolve/references/InVaragReferenceInNamedParameter.kt

@@ -0,0 +1,10 @@
+package test
+
+class A
+
+class Test {
+    fun some(vararg a: A) {}
+    fun call() = some(<caret>a = arrayOf(A()))
+}
+
+// REF: a

idea/tests/org/jetbrains/kotlin/idea/resolve/ReferenceResolveTestGenerated.java

@@ -219,6 +219,11 @@ public class ReferenceResolveTestGenerated extends AbstractReferenceResolveTest
         runTest("idea/testData/resolve/references/InMethodParameter.kt");
     }
 
+    @TestMetadata("InMethodVarargParameter.kt")
+    public void testInMethodVarargParameter() throws Exception {
+        runTest("idea/testData/resolve/references/InMethodVarargParameter.kt");
+    }
+
     @TestMetadata("InObjectClassObject.kt")
     public void testInObjectClassObject() throws Exception {
         runTest("idea/testData/resolve/references/InObjectClassObject.kt");
@@ -229,6 +234,16 @@ public class ReferenceResolveTestGenerated extends AbstractReferenceResolveTest
         runTest("idea/testData/resolve/references/InSecondClassObject.kt");
     }
 
+    @TestMetadata("InVaragReferenceInFunctionBody.kt")
+    public void testInVaragReferenceInFunctionBody() throws Exception {
+        runTest("idea/testData/resolve/references/InVaragReferenceInFunctionBody.kt");
+    }
+
+    @TestMetadata("InVaragReferenceInNamedParameter.kt")
+    public void testInVaragReferenceInNamedParameter() throws Exception {
+        runTest("idea/testData/resolve/references/InVaragReferenceInNamedParameter.kt");
+    }
+
     @TestMetadata("JavaAnnotationParameter.kt")
     public void testJavaAnnotationParameter() throws Exception {
         runTest("idea/testData/resolve/references/JavaAnnotationParameter.kt");