[java-inspections] IDEA-374922 Highlight the second main method as unused (part of IDEA-372969 WIP)

GitOrigin-RevId: 11bc0dcd62d29f94270781ea5a79f4665575d0a9

java/java-analysis-impl/src/com/intellij/codeInspection/reference/RefMethodImpl.java

@@ -7,6 +7,7 @@ import com.intellij.openapi.application.ReadAction;
 import com.intellij.openapi.util.Predicates;
 import com.intellij.openapi.util.text.Strings;
 import com.intellij.psi.*;
+import com.intellij.psi.impl.PsiClassImplUtil;
 import com.intellij.psi.impl.light.LightElement;
 import com.intellij.psi.search.GlobalSearchScope;
 import com.intellij.psi.util.*;
@@ -134,7 +135,9 @@ public sealed class RefMethodImpl extends RefJavaElementImpl implements RefMetho
   }
 
   private static boolean isAppMain(PsiMethod psiMethod, RefMethod refMethod) {
-    if ("main".equals(psiMethod.getName()) && PsiMethodUtil.isMainMethod(psiMethod)) return true;
+    if ("main".equals(psiMethod.getName()) && PsiClassImplUtil.isMainOrPremainMethod(psiMethod)) {
+      return true;
+    }
 
     if (!refMethod.isStatic()) return false;
     if (!PsiTypes.voidType().equals(psiMethod.getReturnType())) return false;

java/java-psi-api/src/com/intellij/psi/util/PsiMethodUtil.java

@@ -55,7 +55,7 @@ public final class PsiMethodUtil {
 
   private PsiMethodUtil() { }
 
-  public static @Nullable PsiMethod findMainMethod(final PsiClass aClass) {
+  public static @Nullable PsiMethod findMainMethod(@NotNull final PsiClass aClass) {
     JavaMainMethodProvider mainMethodProvider = getApplicableMainMethodProvider(aClass);
     if (mainMethodProvider != null) {
       return mainMethodProvider.findMainInClass(aClass);

java/java-psi-impl/src/com/intellij/psi/impl/PsiClassImplUtil.java

@@ -328,17 +328,22 @@ public final class PsiClassImplUtil {
 
   public static boolean isMainOrPremainMethod(@NotNull PsiMethod method) {
     if ("main".equals(method.getName()) && PsiMethodUtil.isMainMethod(method)) {
-      return true;
+      PsiClass psiClass = method.getContainingClass();
+      PsiManager manager = method.getManager();
+      if (psiClass != null && manager != null) {
+        PsiMethod otherMethod = PsiMethodUtil.findMainMethod(psiClass);
+        //can be used not from this class
+        if (otherMethod == null) return true;
+        return manager.areElementsEquivalent(method, otherMethod);
+      }
     }
     String name = method.getName();
-    if (!("main".equals(name) || "premain".equals(name) || "agentmain".equals(name))) return false;
+    if (!("premain".equals(name) || "agentmain".equals(name))) return false;
     if (!PsiTypes.voidType().equals(method.getReturnType())) return false;
 
     PsiElementFactory factory = JavaPsiFacade.getElementFactory(method.getProject());
     MethodSignature signature = method.getSignature(PsiSubstitutor.EMPTY);
     try {
-      MethodSignature main = createSignatureFromText(factory, "void main(String[] args);");
-      if (MethodSignatureUtil.areSignaturesEqual(signature, main)) return true;
       MethodSignature premain = createSignatureFromText(factory, "void premain(String args, java.lang.instrument.Instrumentation i);");
       if (MethodSignatureUtil.areSignaturesEqual(signature, premain)) return true;
       MethodSignature agentmain = createSignatureFromText(factory, "void agentmain(String args, java.lang.instrument.Instrumentation i);");

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advFixture/MainMethodInInterface.java

@@ -0,0 +1,3 @@
+interface A{
+  default void main(){}
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advFixture/SeveralMainMethods.java

@@ -0,0 +1,8 @@
+void main(String[] <warning descr="Parameter 'args' is never used">args</warning>){
+
+}
+
+
+void <warning descr="Method 'main()' is never used">main</warning>(){
+
+}

java/java-tests/testData/inspection/deadCode/severalMainMethods/expected.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<problems>
+  <problem>
+    <file>Test.java</file>
+    <line>6</line>
+    <highlighted_element>t3</highlighted_element>
+    <problem_class id="unused" severity="WARNING" attribute_key="NOT_USED_ELEMENT_ATTRIBUTES">unused declaration</problem_class>
+    <description>Method is never used.</description>
+  </problem>
+</problems>
+

java/java-tests/testData/inspection/deadCode/severalMainMethods/src/Test.java

@@ -0,0 +1,8 @@
+void main(String[] args){
+
+}
+
+
+void main(){
+
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/daemon/LightUnusedHighlightingFixtureTest.java

@@ -7,6 +7,7 @@ import com.intellij.codeInsight.daemon.ImplicitUsageProvider;
 import com.intellij.codeInsight.intention.IntentionAction;
 import com.intellij.codeInspection.deadCode.UnusedDeclarationInspection;
 import com.intellij.pom.java.JavaFeature;
+import com.intellij.pom.java.LanguageLevel;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiField;
 import com.intellij.psi.PsiNamedElement;
@@ -65,6 +66,20 @@ public class LightUnusedHighlightingFixtureTest extends LightJavaCodeInsightFixt
     });
   }
 
+  public void testSeveralMainMethods() {
+    IdeaTestUtil.withLevel(getModule(), LanguageLevel.JDK_25, ()->{
+      myFixture.configureByFile(getTestName(false) + ".java");
+      myFixture.checkHighlighting();
+    });
+  }
+
+  public void testMainMethodInInterface() {
+    IdeaTestUtil.withLevel(getModule(), LanguageLevel.JDK_25, ()->{
+      myFixture.configureByFile(getTestName(false) + ".java");
+      myFixture.checkHighlighting();
+    });
+  }
+
   @Override
   protected String getBasePath() {
     return JavaTestUtil.getRelativeJavaTestDataPath() + "/codeInsight/daemonCodeAnalyzer/advFixture";

java/java-tests/testSrc/com/intellij/java/codeInspection/UnusedDeclarationInspectionTest.java

@@ -300,6 +300,13 @@ public class UnusedDeclarationInspectionTest extends AbstractUnusedDeclarationTe
     });
   }
 
+  public void testSeveralMainMethods() {
+    IdeaTestUtil.withLevel(getModule(), LanguageLevel.JDK_25, () -> {
+      myTool.ADD_MAINS_TO_ENTRIES = true;
+      doTest();
+    });
+  }
+
   private void doTest5() {
     IdeaTestUtil.withLevel(getModule(), LanguageLevel.JDK_1_5, () -> doTest());
   }