FIR LC: introduce FirLightParameterList

LightParameterListBuilder, as a subtype of PsiParameterList, is good
enough for LightMethod's parameter list abstraction. However, it does
not have a parent link, which bothers upward conversion in UAST
(a.k.a. convertParent APIs). So we need an abstraction similar to
KtLightParameterList (in FE 1.0 LC).

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/asJava/methods/FirLightMethodForSymbol.kt

@@ -6,14 +6,14 @@
 package org.jetbrains.kotlin.idea.asJava
 
 import com.intellij.psi.*
-import com.intellij.psi.impl.light.LightParameterListBuilder
 import org.jetbrains.kotlin.asJava.builder.LightMemberOrigin
 import org.jetbrains.kotlin.asJava.classes.lazyPub
 import org.jetbrains.kotlin.asJava.elements.FirLightIdentifier
+import org.jetbrains.kotlin.idea.asJava.parameters.FirLightParameterList
 import org.jetbrains.kotlin.idea.frontend.api.isValid
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtFunctionLikeSymbol
 import org.jetbrains.kotlin.psi.KtDeclaration
-import java.util.*
+import java.util.BitSet
 
 internal abstract class FirLightMethodForSymbol(
     private val functionSymbol: KtFunctionLikeSymbol,
@@ -31,25 +31,7 @@ internal abstract class FirLightMethodForSymbol(
     override fun isVarArgs(): Boolean = _isVarArgs
 
     private val _parametersList by lazyPub {
-        val builder = LightParameterListBuilder(manager, language)
-
-        FirLightParameterForReceiver.tryGet(functionSymbol, this)?.let {
-            builder.addParameter(it)
-        }
-
-        functionSymbol.valueParameters.mapIndexed { index, parameter ->
-            val needToSkip = argumentsSkipMask?.get(index) == true
-            if (!needToSkip) {
-                builder.addParameter(
-                    FirLightParameterForSymbol(
-                        parameterSymbol = parameter,
-                        containingMethod = this@FirLightMethodForSymbol
-                    )
-                )
-            }
-        }
-
-        builder
+        FirLightParameterList(this, functionSymbol, argumentsSkipMask)
     }
 
     private val _identifier: PsiIdentifier by lazyPub {
@@ -63,4 +45,4 @@ internal abstract class FirLightMethodForSymbol(
     override val kotlinOrigin: KtDeclaration? = functionSymbol.psi as? KtDeclaration
 
     override fun isValid(): Boolean = super.isValid() && functionSymbol.isValid()
-}
+}

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/asJava/parameters/FirLightParameterList.kt

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.idea.asJava.parameters
+
+import com.intellij.psi.PsiParameter
+import com.intellij.psi.PsiParameterList
+import com.intellij.psi.impl.light.LightParameterListBuilder
+import org.jetbrains.kotlin.asJava.classes.lazyPub
+import org.jetbrains.kotlin.asJava.elements.KtLightElement
+import org.jetbrains.kotlin.asJava.elements.KtLightElementBase
+import org.jetbrains.kotlin.idea.asJava.FirLightMethod
+import org.jetbrains.kotlin.idea.asJava.FirLightParameterForReceiver
+import org.jetbrains.kotlin.idea.asJava.FirLightParameterForSymbol
+import org.jetbrains.kotlin.idea.frontend.api.symbols.KtFunctionLikeSymbol
+import org.jetbrains.kotlin.psi.KtFunction
+import org.jetbrains.kotlin.psi.KtParameterList
+import java.util.BitSet
+
+internal class FirLightParameterList(
+    private val parent: FirLightMethod,
+    private val functionSymbol: KtFunctionLikeSymbol,
+    argumentsSkipMask: BitSet? = null
+) : KtLightElement<KtParameterList, PsiParameterList>,
+    // With this, a parent chain is properly built: from FirLightParameter through FirLightParameterList to FirLightMethod
+    KtLightElementBase(parent),
+    // NB: we can't use delegation here, which will conflict getTextRange from KtLightElementBase
+    PsiParameterList {
+
+    override val kotlinOrigin: KtParameterList?
+        get() = (parent.kotlinOrigin as? KtFunction)?.valueParameterList
+
+    override val clsDelegate: PsiParameterList by lazyPub {
+        val builder = LightParameterListBuilder(manager, language)
+
+        FirLightParameterForReceiver.tryGet(functionSymbol, parent)?.let {
+            builder.addParameter(it)
+        }
+
+        functionSymbol.valueParameters.mapIndexed { index, parameter ->
+            val needToSkip = argumentsSkipMask?.get(index) == true
+            if (!needToSkip) {
+                builder.addParameter(
+                    FirLightParameterForSymbol(
+                        parameterSymbol = parameter,
+                        containingMethod = parent
+                    )
+                )
+            }
+        }
+
+        builder
+    }
+
+    override fun getParameters(): Array<PsiParameter> {
+        return clsDelegate.parameters
+    }
+
+    override fun getParameterIndex(p: PsiParameter): Int {
+        return clsDelegate.getParameterIndex(p)
+    }
+
+    override fun getParametersCount(): Int {
+        return clsDelegate.parametersCount
+    }
+}