Add inspection for switches on enum mixins

Author: Earthcomputer

src/main/kotlin/platform/mixin/inspection/EnumMixinSwitchStatementInspection.kt

@@ -0,0 +1,84 @@
+/*
+ * Minecraft Development for IntelliJ
+ *
+ * https://mcdev.io/
+ *
+ * Copyright (C) 2026 minecraft-dev
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, version 3.0 only.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.demonwav.mcdev.platform.mixin.inspection
+
+import com.demonwav.mcdev.platform.mixin.util.isMixin
+import com.demonwav.mcdev.platform.mixin.util.mixinTargets
+import com.intellij.codeInspection.LocalQuickFix
+import com.intellij.codeInspection.LocalQuickFixOnPsiElement
+import com.intellij.codeInspection.ProblemsHolder
+import com.intellij.openapi.project.Project
+import com.intellij.psi.JavaElementVisitor
+import com.intellij.psi.JavaPsiFacade
+import com.intellij.psi.PsiElement
+import com.intellij.psi.PsiExpression
+import com.intellij.psi.PsiFile
+import com.intellij.psi.PsiSwitchBlock
+import com.intellij.psi.PsiSwitchExpression
+import com.intellij.psi.PsiSwitchStatement
+import com.intellij.psi.PsiTypeCastExpression
+import com.intellij.psi.codeStyle.JavaCodeStyleManager
+import com.intellij.psi.util.PsiTypesUtil
+
+class EnumMixinSwitchStatementInspection : MixinInspection() {
+    override fun getStaticDescription() = "Reports when a switch statement or expression is used on an enum mixin"
+
+    override fun buildVisitor(holder: ProblemsHolder) = object : JavaElementVisitor() {
+        override fun visitSwitchStatement(statement: PsiSwitchStatement) {
+            visitSwitchBlock(statement)
+        }
+
+        override fun visitSwitchExpression(expression: PsiSwitchExpression) {
+            visitSwitchBlock(expression)
+        }
+
+        private fun visitSwitchBlock(block: PsiSwitchBlock) {
+            val expression = block.expression ?: return
+            val mixinClass = PsiTypesUtil.getPsiClass(expression.type) ?: return
+            if (!mixinClass.isEnum || !mixinClass.isMixin) {
+                return
+            }
+
+            val fixes = mutableListOf<LocalQuickFix>()
+            val targetClass = mixinClass.mixinTargets.singleOrNull()
+            if (targetClass != null) {
+                fixes += AddCastFix(expression, targetClass.name)
+            }
+            holder.registerProblem(expression, "Switch used on enum mixin", *fixes.toTypedArray())
+        }
+    }
+
+    private class AddCastFix(expression: PsiExpression, private val targetClass: String) : LocalQuickFixOnPsiElement(expression) {
+        override fun getFamilyName() = "Add double cast to ${targetClass.substringAfterLast('/').replace('$', '.')}"
+        override fun getText() = "Add cast to target class ${targetClass.substringAfterLast('/').replace('$', '.')}"
+
+        override fun invoke(project: Project, psiFile: PsiFile, startElement: PsiElement, endElement: PsiElement) {
+            val expression = startElement as? PsiExpression ?: return
+            val doubleCast = JavaPsiFacade.getElementFactory(project).createExpressionFromText(
+                "(${targetClass.replace('/', '.').replace('$', '.')}) (java.lang.Object) x",
+                expression
+            ) as PsiTypeCastExpression
+            (doubleCast.operand as PsiTypeCastExpression).operand!!.replace(expression)
+            val resultingExpression = expression.replace(doubleCast)
+            JavaCodeStyleManager.getInstance(project).shortenClassReferences(resultingExpression)
+        }
+    }
+}

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

@@ -1114,6 +1114,14 @@
                          level="WARNING"
                          hasStaticDescription="true"
                          implementationClass="com.demonwav.mcdev.platform.mixin.inspection.StaticMemberInspection"/>
+        <localInspection displayName="Switch used on an enum mixin"
+                         shortName="SwitchOnEnumMixin"
+                         groupName="Mixin"
+                         language="JAVA"
+                         enabledByDefault="true"
+                         level="ERROR"
+                         hasStaticDescription="true"
+                         implementationClass="com.demonwav.mcdev.platform.mixin.inspection.EnumMixinSwitchStatementInspection"/>
         <localInspection displayName="Inner classes in Mixins"
                          shortName="MixinInnerClass"
                          groupName="Mixin"