Feature: introduce variable

src/main/scala/intellij/haskell/psi/stubs/HaskellConidStub.java

@@ -27,7 +27,7 @@ public HaskellConidStub(StubElement parent, IStubElementType elementType, String
         super(parent, elementType, name);
     }
 
-    public HaskellConidStub(StubElement parent, IStubElementType elementType, String name) {
+    public HaskellConidStub(StubElement<?> parent, IStubElementType elementType, String name) {
         super(parent, elementType, name);
     }
 }

src/main/scala/intellij/haskell/psi/stubs/HaskellConsymStub.java

@@ -27,7 +27,7 @@ public HaskellConsymStub(StubElement parent, IStubElementType elementType, Strin
         super(parent, elementType, name);
     }
 
-    public HaskellConsymStub(StubElement parent, IStubElementType elementType, String name) {
+    public HaskellConsymStub(StubElement<?> parent, IStubElementType elementType, String name) {
         super(parent, elementType, name);
     }
 }

src/main/scala/intellij/haskell/psi/stubs/HaskellModidStub.java

@@ -27,7 +27,7 @@ public HaskellModidStub(StubElement parent, IStubElementType elementType, String
         super(parent, elementType, name);
     }
 
-    public HaskellModidStub(StubElement parent, IStubElementType elementType, String name) {
+    public HaskellModidStub(StubElement<?> parent, IStubElementType elementType, String name) {
         super(parent, elementType, name);
     }
 }

src/main/scala/intellij/haskell/psi/stubs/HaskellVaridStub.java

@@ -27,7 +27,7 @@ public HaskellVaridStub(StubElement parent, IStubElementType elementType, String
         super(parent, elementType, name);
     }
 
-    public HaskellVaridStub(StubElement parent, IStubElementType elementType, String name) {
+    public HaskellVaridStub(StubElement<?> parent, IStubElementType elementType, String name) {
         super(parent, elementType, name);
     }
 }

src/main/scala/intellij/haskell/psi/stubs/HaskellVarsymStub.java

@@ -27,7 +27,7 @@ public HaskellVarsymStub(StubElement parent, IStubElementType elementType, Strin
         super(parent, elementType, name);
     }
 
-    public HaskellVarsymStub(StubElement parent, IStubElementType elementType, String name) {
+    public HaskellVarsymStub(StubElement<?> parent, IStubElementType elementType, String name) {
         super(parent, elementType, name);
     }
 }

src/main/scala/intellij/haskell/psi/stubs/types/HaskellConidStubElementType.scala

@@ -27,7 +27,7 @@ class HaskellConidStubElementType(debugName: String) extends HaskellNamedStubEle
     new HaskellConidImpl(stub, this)
   }
 
-  def createStub(psi: HaskellConid, parentStub: StubElement[_ <: PsiElement]): HaskellConidStub = {
+  def createStub(psi: HaskellConid, parentStub: StubElement[_]): HaskellConidStub = {
     new HaskellConidStub(parentStub, this, psi.getName)
   }
 

src/main/scala/intellij/haskell/psi/stubs/types/HaskellConsymStubElementType.scala

@@ -27,7 +27,7 @@ class HaskellConsymStubElementType(debugName: String) extends HaskellNamedStubEl
     new HaskellConsymImpl(stub, this)
   }
 
-  def createStub(psi: HaskellConsym, parentStub: StubElement[_ <: PsiElement]): HaskellConsymStub = {
+  def createStub(psi: HaskellConsym, parentStub: StubElement[_]): HaskellConsymStub = {
     new HaskellConsymStub(parentStub, this, psi.getName)
   }
 

src/main/scala/intellij/haskell/psi/stubs/types/HaskellModidStubElementType.scala

@@ -27,7 +27,7 @@ class HaskellModidStubElementType(debugName: String) extends HaskellNamedStubEle
     new HaskellModidImpl(stub, this)
   }
 
-  def createStub(psi: HaskellModid, parentStub: StubElement[_ <: PsiElement]): HaskellModidStub = {
+  def createStub(psi: HaskellModid, parentStub: StubElement[_]): HaskellModidStub = {
     new HaskellModidStub(parentStub, this, psi.getName)
   }
 

src/main/scala/intellij/haskell/psi/stubs/types/HaskellVaridStubElementType.scala

@@ -27,7 +27,7 @@ class HaskellVaridStubElementType(debugName: String) extends HaskellNamedStubEle
     new HaskellVaridImpl(stub, this)
   }
 
-  def createStub(psi: HaskellVarid, parentStub: StubElement[_ <: PsiElement]): HaskellVaridStub = {
+  def createStub(psi: HaskellVarid, parentStub: StubElement[_]): HaskellVaridStub = {
     new HaskellVaridStub(parentStub, this, psi.getName)
   }
 

src/main/scala/intellij/haskell/psi/stubs/types/HaskellVarsymStubElementType.scala

@@ -11,7 +11,7 @@ class HaskellVarsymStubElementType(debugName: String) extends HaskellNamedStubEl
     new HaskellVarsymImpl(stub, this)
   }
 
-  def createStub(psi: HaskellVarsym, parentStub: StubElement[_ <: PsiElement]): HaskellVarsymStub = {
+  def createStub(psi: HaskellVarsym, parentStub: StubElement[_]): HaskellVarsymStub = {
     new HaskellVarsymStub(parentStub, this, psi.getName)
   }
 

src/main/scala/intellij/haskell/refactor/HaskellRefactoringSupportProvider.scala

@@ -17,7 +17,14 @@
 package intellij.haskell.refactor
 
 import com.intellij.lang.refactoring.RefactoringSupportProvider
+import com.intellij.openapi.actionSystem.DataContext
+import com.intellij.openapi.command.WriteCommandAction.writeCommandAction
+import com.intellij.openapi.editor.{Editor, SelectionModel}
+import com.intellij.openapi.project.Project
 import com.intellij.psi._
+import com.intellij.psi.util.PsiTreeUtil
+import com.intellij.refactoring.RefactoringActionHandler
+import intellij.haskell.psi.HaskellExpression
 import intellij.haskell.util.HaskellProjectUtil
 
 class HaskellRefactoringSupportProvider extends RefactoringSupportProvider {
@@ -32,4 +39,34 @@ class HaskellRefactoringSupportProvider extends RefactoringSupportProvider {
       case _ => false
     }
   }
-}
+
+  override def getIntroduceVariableHandler: RefactoringActionHandler = {
+    new RefactoringActionHandler {
+      override def invoke(project: Project, editor: Editor, file: PsiFile, dataContext: DataContext): Unit = {
+        val model: SelectionModel = editor.getSelectionModel
+
+        if (!model.hasSelection) return
+
+        val element1: PsiElement = file.findElementAt(model.getSelectionStart)
+        val element2: PsiElement = file.findElementAt(model.getSelectionEnd - 1)
+
+        // Ideally, once we fix the parser, this would be the expression selection
+        var parent = PsiTreeUtil.findCommonParent(element1, element2)
+        parent = PsiTreeUtil.getParentOfType[HaskellExpression](parent, classOf[HaskellExpression])
+
+        if (!(parent != null
+          && PsiTreeUtil.getDeepestFirst(parent) == element1
+          && PsiTreeUtil.getDeepestLast(parent) == element2))
+          return
+
+        writeCommandAction(project, file).withName("Introduce Variable").withGroupId(null).run(() => {
+          editor.getDocument.replaceString(model.getSelectionStart, model.getSelectionEnd, "x")
+        })
+      }
+
+      override def invoke(project: Project, elements: Array[PsiElement], dataContext: DataContext): Unit = {
+        // This does not get called
+      }
+    }
+  }
+}