Add ForgeImplicitUsageProvider to mark coremod classes as used

Closes #237

Author: stephan-gh

src/main/kotlin/com/demonwav/mcdev/platform/forge/insight/ForgeImplicitUsageProvider.kt

@@ -0,0 +1,30 @@
+/*
+ * Minecraft Dev for IntelliJ
+ *
+ * https://minecraftdev.org
+ *
+ * Copyright (c) 2017 minecraft-dev
+ *
+ * MIT License
+ */
+
+package com.demonwav.mcdev.platform.forge.insight
+
+import com.demonwav.mcdev.platform.forge.util.ForgeConstants
+import com.demonwav.mcdev.util.extendsOrImplements
+import com.intellij.codeInsight.daemon.ImplicitUsageProvider
+import com.intellij.psi.PsiClass
+import com.intellij.psi.PsiElement
+
+class ForgeImplicitUsageProvider : ImplicitUsageProvider {
+
+    override fun isImplicitUsage(element: PsiElement) = isCoreMod(element)
+
+    fun isCoreMod(element: PsiElement): Boolean {
+        return element is PsiClass && element.extendsOrImplements(ForgeConstants.CORE_MOD_INTERFACE)
+    }
+
+    override fun isImplicitRead(element: PsiElement) = false
+    override fun isImplicitWrite(element: PsiElement) = false
+
+}

src/main/kotlin/com/demonwav/mcdev/platform/forge/util/ForgeConstants.kt

@@ -16,6 +16,7 @@ object ForgeConstants {
     const val SIDE_ANNOTATION = "net.minecraftforge.fml.relauncher.Side"
     const val SIDED_PROXY_ANNOTATION = "net.minecraftforge.fml.common.SidedProxy"
     const val MOD_ANNOTATION = "net.minecraftforge.fml.common.Mod"
+    const val CORE_MOD_INTERFACE = "net.minecraftforge.fml.relauncher.IFMLLoadingPlugin"
     const val EVENT_HANDLER_ANNOTATION = "net.minecraftforge.fml.common.Mod.EventHandler"
     const val SUBSCRIBE_EVENT_ANNOTATION = "net.minecraftforge.fml.common.eventhandler.SubscribeEvent"
     const val FML_EVENT = "net.minecraftforge.fml.common.event.FMLEvent"

src/main/resources/META-INF/plugin.xml

@@ -132,6 +132,7 @@
         <!---->
 
         <fileIconProvider implementation="com.demonwav.mcdev.platform.forge.ForgeFileIconProvider"/>
+        <implicitUsageProvider implementation="com.demonwav.mcdev.platform.forge.insight.ForgeImplicitUsageProvider" />
 
         <!-- Forge Annotator -->
         <annotator language="JAVA" implementationClass="com.demonwav.mcdev.platform.forge.inspections.sideonly.SidedProxyAnnotator"/>