Enabling Haskell custom tools should be all or nothing.

src/main/scala/intellij/haskell/external/component/StackProjectManager.scala

@@ -26,9 +26,8 @@ import com.intellij.openapi.project.Project
 import com.intellij.openapi.projectRoots.ProjectJdkTable
 import com.intellij.openapi.roots.{ModifiableRootModel, ModuleRootModificationUtil}
 import com.intellij.openapi.ui.Messages
-import com.intellij.openapi.util.SystemInfo
 import com.intellij.openapi.vfs.VirtualFileManager
-import intellij.haskell.action.{HaskellReformatAction, HindentReformatAction, StylishHaskellReformatAction}
+import intellij.haskell.action.HaskellReformatAction
 import intellij.haskell.annotator.HaskellAnnotator
 import intellij.haskell.external.execution.StackCommandLine
 import intellij.haskell.external.repl.StackRepl.LibType
@@ -111,7 +110,7 @@ object StackProjectManager {
     ProgressManager.getInstance().run(new Task.Backgroundable(project, title, false, PerformInBackgroundOption.ALWAYS_BACKGROUND) {
 
       private def isToolAvailable(progressIndicator: ProgressIndicator, tool: HTool) = {
-        HaskellSettingsState.useCustomTool(tool) || {
+        HaskellSettingsState.useCustomTools || {
           if (!GlobalInfo.toolPath(tool).exists() || update) {
             progressIndicator.setText(s"Busy with installing ${tool.name} in ${GlobalInfo.toolsBinPath}")
             StackCommandLine.installTool(project, tool.name)

src/main/scala/intellij/haskell/settings/HaskellConfigurable.scala

@@ -21,7 +21,7 @@ import java.awt.{GridBagConstraints, GridBagLayout, Insets}
 import com.intellij.openapi.options.{Configurable, ConfigurationException}
 import com.intellij.ui.DocumentAdapter
 import javax.swing._
-import javax.swing.event.{ChangeListener, DocumentEvent}
+import javax.swing.event.DocumentEvent
 
 class HaskellConfigurable extends Configurable {
   private var isModifiedByUser = false
@@ -123,7 +123,7 @@ class HaskellConfigurable extends Configurable {
       (new JLabel(BuildToolsUsingSystemGhc), useSystemGhcToggle),
       (new JLabel(UseCustomTool), useCustomToolsToggle),
       (new JLabel(""), afterRestartLabel),
-      (new JLabel(""),  {
+      (new JLabel(""), {
         val x = new JTextArea(PathWarning)
         x.setLineWrap(true)
         x.setWrapStyleWord(true)
@@ -151,6 +151,9 @@ class HaskellConfigurable extends Configurable {
     val validREPLTimeout = validateREPLTimeout()
 
     val state = HaskellSettingsPersistentStateComponent.getInstance().getState
+
+    validateCustomTools()
+
     state.replTimeout = validREPLTimeout
     state.hlintOptions = hlintOptionsField.getText
     state.useSystemGhc = useSystemGhcToggle.isSelected
@@ -175,6 +178,18 @@ class HaskellConfigurable extends Configurable {
     timeout
   }
 
+  private def validateCustomTools(): Unit = {
+    if (useCustomToolsToggle.isSelected) {
+      if (hindentPathField.getText.trim.isEmpty ||
+        hlintPathField.getText.trim.isEmpty ||
+        hooglePathField.getText.trim.isEmpty ||
+        stylishHaskellPathField.getText.trim.isEmpty) {
+        throw new ConfigurationException(s"All Haskell tools paths have to be set")
+      }
+    }
+  }
+
+
   override def disposeUIResources(): Unit = {}
 
   override def getHelpTopic: String = ""

src/main/scala/intellij/haskell/settings/HaskellSettingsState.scala

@@ -16,8 +16,6 @@
 
 package intellij.haskell.settings
 
-import intellij.haskell.HTool
-
 object HaskellSettingsState {
   private def state = HaskellSettingsPersistentStateComponent.getInstance().getState
 
@@ -73,10 +71,8 @@ object HaskellSettingsState {
     Option.when(customTools && state.stylishHaskellPath.nonEmpty)(state.stylishHaskellPath)
   }
 
-  def useCustomTool(tool: HTool): Boolean = tool match {
-    case HTool.Hindent => hindentPath.isDefined
-    case HTool.Hlint => hlintPath.isDefined
-    case HTool.Hoogle => hooglePath.isDefined
-    case HTool.StylishHaskell => stylishHaskellPath.isDefined
+  def useCustomTools: Boolean = {
+    state.customTools
   }
+
 }