Introduce Type Alias

#KT-12902 Fixed

compiler/frontend/src/org/jetbrains/kotlin/psi/KtPsiFactory.kt

@@ -98,11 +98,19 @@ class KtPsiFactory(private val project: Project) {
         return typeReference
     }
 
+    fun createType(typeElement: KtTypeElement) = createType("X").apply { this.typeElement!!.replace(typeElement) }
+
     fun createTypeIfPossible(type: String): KtTypeReference? {
         val typeReference = createProperty("val x : $type").typeReference
         return if (typeReference?.text == type) typeReference else null
     }
 
+    fun createTypeAlias(name: String, typeParameters: List<String>, typeElement: KtTypeElement): KtTypeAlias {
+        val typeParametersText = if (typeParameters.isNotEmpty()) typeParameters.joinToString(prefix = "<", postfix = ">") else ""
+        return createDeclaration<KtTypeAlias>("typealias $name$typeParametersText = X")
+                .apply { getTypeReference()!!.replace(createType(typeElement)) }
+    }
+
     fun createStar(): PsiElement {
         return createType("List<*>").findElementAt(5)!!
     }

compiler/frontend/src/org/jetbrains/kotlin/psi/KtTypeArgumentList.java

@@ -41,4 +41,9 @@ public class KtTypeArgumentList extends KtElementImplStub<KotlinPlaceHolderStub<
     public List<KtTypeProjection> getArguments() {
         return getStubOrPsiChildrenAsList(KtStubElementTypes.TYPE_PROJECTION);
     }
+
+    @NotNull
+    public KtTypeProjection addArgument(@NotNull KtTypeProjection argument) {
+        return EditCommaSeparatedListHelper.INSTANCE.addItem(this, getArguments(), argument);
+    }
 }

compiler/frontend/src/org/jetbrains/kotlin/psi/psiUtil/psiUtils.kt

@@ -140,6 +140,10 @@ fun PsiElement.getNextSiblingIgnoringWhitespaceAndComments(): PsiElement? {
     return siblings(withItself = false).filter { it !is PsiWhiteSpace && it !is PsiComment }.firstOrNull()
 }
 
+fun PsiElement.getPrevSiblingIgnoringWhitespaceAndComments(): PsiElement? {
+    return siblings(withItself = false, forward = false).filter { it !is PsiWhiteSpace && it !is PsiComment }.firstOrNull()
+}
+
 inline fun <reified T : PsiElement> T.nextSiblingOfSameType() = PsiTreeUtil.getNextSiblingOfType(this, T::class.java)
 
 inline fun <reified T : PsiElement> T.prevSiblingOfSameType() = PsiTreeUtil.getPrevSiblingOfType(this, T::class.java)