[IR] Support hidden parameters in IrMangler

- make them be skipped in signature

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/mangle/ir/IrMangleComputer.kt

@@ -5,9 +5,7 @@
 
 package org.jetbrains.kotlin.backend.common.serialization.mangle.ir
 
-import org.jetbrains.kotlin.backend.common.serialization.mangle.KotlinMangleComputer
+import org.jetbrains.kotlin.backend.common.serialization.mangle.*
-import org.jetbrains.kotlin.backend.common.serialization.mangle.MangleConstant
-import org.jetbrains.kotlin.backend.common.serialization.mangle.MangleMode
 import org.jetbrains.kotlin.backend.common.serialization.mangle.collectForMangler
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
@@ -106,14 +104,19 @@ abstract class IrMangleComputer(protected val builder: StringBuilder, private va
         }
 
         extensionReceiverParameter?.let {
-            builder.appendSignature(MangleConstant.EXTENSION_RECEIVER_PREFIX)
+            if (!it.isHidden) {
-            mangleValueParameter(builder, it)
+                builder.appendSignature(MangleConstant.EXTENSION_RECEIVER_PREFIX)
+                mangleValueParameter(builder, it)
+            }
         }
 
         valueParameters.collectForMangler(builder, MangleConstant.VALUE_PARAMETERS) {
-            appendSignature(specialValueParamPrefix(it))
+            if (!it.isHidden) {
-            mangleValueParameter(this, it)
+                appendSignature(specialValueParamPrefix(it))
+                mangleValueParameter(this, it)
+            }
         }
+
         typeParameters.collectForMangler(builder, MangleConstant.TYPE_PARAMETERS) { mangleTypeParameter(this, it) }
 
         if (!isCtor && !returnType.isUnit() && addReturnType()) {

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/mangle/mangleUtils.kt

@@ -12,14 +12,25 @@ fun <T> Collection<T>.collectForMangler(builder: StringBuilder, params: MangleCo
 
     builder.append(params.prefix)
 
+    var addSeparator = true
+
     for (e in this) {
         if (first) {
             first = false
-        } else {
+        } else if (addSeparator) {
             builder.append(params.separator)
         }
 
+        val l = builder.length
         builder.collect(e)
+        addSeparator = l < builder.length
+    }
+
+    if (!addSeparator) {
+        if (builder.last() == params.separator) {
+            // avoid signatures like foo(Int;)
+            builder.deleteCharAt(builder.lastIndex)
+        }
     }
 
     builder.append(params.suffix)