openide/java/java-impl-inspections/src/com/intellij/codeInspection/ExplicitToImplicitClassMigrationInspection.java

// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
package com.intellij.codeInspection;

import com.intellij.codeInsight.TestFrameworks;
import com.intellij.codeInsight.daemon.impl.UnusedSymbolUtil;
import com.intellij.codeInspection.options.OptPane;
import com.intellij.ide.highlighter.JavaFileType;
import com.intellij.java.JavaBundle;
import com.intellij.java.codeserver.core.JavaPsiModuleUtil;
import com.intellij.modcommand.*;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.roots.ProjectFileIndex;
import com.intellij.openapi.roots.ProjectRootManager;
import com.intellij.openapi.util.TextRange;
import com.intellij.openapi.vfs.VirtualFile;
import com.intellij.pom.java.JavaFeature;
import com.intellij.psi.*;
import com.intellij.psi.codeStyle.JavaCodeStyleManager;
import com.intellij.psi.search.GlobalSearchScope;
import com.intellij.psi.search.PackageScope;
import com.intellij.psi.search.PsiSearchHelper;
import com.intellij.psi.search.SearchScope;
import com.intellij.psi.search.searches.ReferencesSearch;
import com.intellij.psi.util.PsiMethodUtil;
import com.intellij.psi.util.PsiTreeUtil;
import com.intellij.psi.util.PsiUtil;
import com.intellij.util.ObjectUtils;
import com.siyeh.ig.psiutils.CommentTracker;
import com.siyeh.ig.psiutils.VariableAccessUtils;
import com.siyeh.ipp.imports.ReplaceOnDemandImportIntention;
import org.jetbrains.annotations.Nls;
import org.jetbrains.annotations.NotNull;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;

public final class ExplicitToImplicitClassMigrationInspection extends AbstractBaseJavaLocalInspectionTool {

  public boolean convertToIo = true;

  @Override
  public @NotNull Set<@NotNull JavaFeature> requiredFeatures() {
    return Set.of(JavaFeature.IMPLICIT_CLASSES);
  }

  @Override
  public @NotNull OptPane getOptionsPane() {
    return OptPane.pane(
      OptPane.checkbox("convertToIo",
                       JavaBundle.message("inspection.explicit.to.implicit.convert.to.io"))
    );
  }

  @Override
  public @NotNull PsiElementVisitor buildVisitor(@NotNull ProblemsHolder holder, boolean isOnTheFly) {
    return new JavaElementVisitor() {
      @Override
      public void visitClass(@NotNull PsiClass aClass) {
        if (aClass.isInterface() || aClass.isRecord() || aClass.isEnum() || PsiUtil.isLocalOrAnonymousClass(aClass)) {
          return;
        }

        if (aClass.getAnnotations().length > 0) return;

        PsiElement lBrace = aClass.getLBrace();
        PsiElement rBrace = aClass.getRBrace();
        if (lBrace == null || rBrace == null) {
          return;
        }

        if (aClass.getContainingClass() != null) {
          return;
        }
        PsiFile file = aClass.getContainingFile();
        if (!(file instanceof PsiJavaFile javaFile)) return;
        boolean underRoot = javaFile.getPackageStatement() == null;

        if (javaFile.getClasses().length != 1) {
          return;
        }

        PsiJavaModule javaModule = JavaPsiModuleUtil.findDescriptorByElement(aClass);
        if (javaModule != null) {
          return;
        }

        String fileName = file.getName();
        if (!fileName.endsWith(JavaFileType.DOT_DEFAULT_EXTENSION)) {
          return;
        }

        String className = aClass.getName();
        if (className == null ||
            !className.equals(fileName.substring(0, fileName.length() - JavaFileType.DOT_DEFAULT_EXTENSION.length()))) {
          return;
        }

        if (aClass.hasTypeParameters()) {
          return;
        }

        if (!PsiMethodUtil.hasMainMethod(aClass)) {
          return;
        }

        PsiClassType[] extendsListTypes = aClass.getExtendsListTypes();
        if ((extendsListTypes.length != 0 && !onlyObjectExtends(extendsListTypes)) ||
            aClass.getImplementsListTypes().length != 0) {
          return;
        }

        if (aClass.hasModifierProperty(PsiModifier.SEALED) || aClass.hasModifierProperty(PsiModifier.ABSTRACT)) {
          return;
        }

        PsiMethod[] constructors = aClass.getConstructors();
        if (constructors.length > 0) {
          if (constructors.length > 1) {
            return;
          }

          PsiMethod constructor = constructors[0];
          if (constructor.hasParameters() ||
              constructor.hasModifierProperty(PsiModifier.PRIVATE) ||
              (constructor.getBody() != null && constructor.getBody().getStatements().length > 0)) {
            return;
          }
        }

        Project project = holder.getProject();
        PsiIdentifier classIdentifier = aClass.getNameIdentifier();
        if (classIdentifier == null) {
          return;
        }

        if (TestFrameworks.getInstance().isTestClass(aClass) ||
            UnusedSymbolUtil.isImplicitUsage(aClass.getProject(), aClass)) {
          return;
        }

        SearchScope scope;
        if (underRoot) {
          PsiPackage aPackage = JavaPsiFacade.getInstance(project).findPackage("");
          if (aPackage == null) {
            return;
          }
          scope = new PackageScope(aPackage, false, false);
        }
        else {
          scope = aClass.getUseScope();
        }

        if (isOnTheFly && scope instanceof GlobalSearchScope globalSearchScope) {
          final PsiSearchHelper searchHelper = PsiSearchHelper.getInstance(project);
          final PsiSearchHelper.SearchCostResult cost =
            searchHelper.isCheapEnoughToSearch(className, globalSearchScope, null);
          if (cost == PsiSearchHelper.SearchCostResult.TOO_MANY_OCCURRENCES) {
            holder.registerPossibleProblem(aClass);
            return;
          }
        }

        PsiReference first = ReferencesSearch.search(aClass, scope).findFirst();
        if (first != null) {
          return;
        }

        if (PsiTreeUtil.hasErrorElements(aClass)) {
          return;
        }
        if (underRoot) {
          holder.registerProblem(aClass, new TextRange(0, classIdentifier.getTextRangeInParent().getEndOffset()),
                                 JavaBundle.message("inspection.explicit.to.implicit.class.migration.name"),
                                 new ReplaceWithImplicitClassFix(convertToIo));
        }
        else {
          holder.registerProblem(aClass,
                                 JavaBundle.message("inspection.explicit.to.implicit.class.migration.name"),
                                 ProblemHighlightType.INFORMATION,
                                 new TextRange(0, classIdentifier.getTextRangeInParent().getEndOffset()),
                                 new ReplaceWithImplicitClassFix(convertToIo));
        }
      }

      private static boolean onlyObjectExtends(PsiClassType[] types) {
        if (types.length != 1) return false;
        PsiClassType type = types[0];
        return type.equalsToText(CommonClassNames.JAVA_LANG_OBJECT);
      }
    };
  }


  private static class ReplaceWithImplicitClassFix extends ModCommandQuickFix {

    private final boolean myConvertToIo;

    private ReplaceWithImplicitClassFix(boolean io) { myConvertToIo = io; }

    @Override
    public @Nls(capitalization = Nls.Capitalization.Sentence) @NotNull String getFamilyName() {
      return JavaBundle.message("inspection.explicit.to.implicit.class.migration.fix.name");
    }

    @Override
    public final @NotNull ModCommand perform(@NotNull Project project, @NotNull ProblemDescriptor descriptor) {
      PsiElement element = descriptor.getStartElement();
      PsiFile file = element.getContainingFile();
      if (!(file instanceof PsiJavaFile javaFile)) return ModCommand.nop();
      PsiPackageStatement statement = javaFile.getPackageStatement();
      ProjectFileIndex fileIndex = ProjectRootManager.getInstance(project).getFileIndex();
      VirtualFile sourceRoot = fileIndex.getSourceRootForFile(javaFile.getVirtualFile());
      if (statement == null || sourceRoot == null) {
        return ModCommand
          .psiUpdate(element, (e, updater) -> applyFix(project, e));
      }
      return ModCommand.chooseAction(
        JavaBundle.message("inspection.explicit.to.implicit.move.to.root.title"),
        getCommandActionWithMovingToRoot(project),
        ModCommand.psiUpdateStep(element, JavaBundle.message("inspection.explicit.to.implicit.move.to.root.delete.package"),
                                 (e, updater) -> applyFix(project, e))
      );
    }

    private @NotNull ModCommandAction getCommandActionWithMovingToRoot(@NotNull Project project) {
      return new ModCommandAction() {
        @Override
        public Presentation getPresentation(@NotNull ActionContext context) {
          return Presentation.of(getFamilyName());
        }

        @Override
        public @NotNull ModCommand perform(@NotNull ActionContext context) {
          int offset = context.offset();
          PsiElement element = context.file().findElementAt(offset);
          if (element == null) return ModCommand.nop();
          PsiClass psiClass = PsiTreeUtil.getParentOfType(element, PsiClass.class, false);
          if (psiClass == null) return ModCommand.nop();
          PsiFile containingFile = psiClass.getContainingFile();
          if (containingFile == null) return ModCommand.nop();
          ModCommand modCommand = ModCommand
            .psiUpdate(psiClass, (e, updater) -> applyFix(project, e));
          VirtualFile from = containingFile.getVirtualFile();
          ProjectFileIndex fileIndex = ProjectRootManager.getInstance(project).getFileIndex();
          VirtualFile sourceRoot = fileIndex.getSourceRootForFile(from);
          if (sourceRoot != null) {
            modCommand = modCommand
              .andThen(
                ModCommand.moveFile(from, sourceRoot)
              );
          }
          return modCommand;
        }

        @Override
        public @NotNull String getFamilyName() {
          return JavaBundle.message("inspection.explicit.to.implicit.move.to.root.move");
        }
      };
    }

    private void applyFix(@NotNull Project project, @NotNull PsiElement element) {
      PsiFile containingFile = element.getContainingFile();
      if (!(containingFile instanceof PsiJavaFile javaFile)) {
        return;
      }
      PsiPackageStatement packageStatement = javaFile.getPackageStatement();
      if (packageStatement != null) {
        new CommentTracker().deleteAndRestoreComments(packageStatement);
      }
      PsiImportList list = javaFile.getImportList();
      if (list != null) {
        List<SmartPsiElementPointer<PsiImportStatementBase>> pointers = new ArrayList<>();
        PsiImportStatementBase[] statements = list.getAllImportStatements();
        for (PsiImportStatementBase statement : statements) {
          SmartPsiElementPointer<PsiImportStatementBase> pointer = SmartPointerManager.createPointer(statement);
          pointers.add(pointer);
        }

        for (SmartPsiElementPointer<PsiImportStatementBase> pointer : pointers) {
          PsiImportStatementBase importStatementBase = pointer.getElement();
          if (importStatementBase == null) continue;
          if (!importStatementBase.isOnDemand()) continue;
          ReplaceOnDemandImportIntention.replaceOnDemand(importStatementBase);
        }
      }
      PsiClass psiClass = ObjectUtils.tryCast(element, PsiClass.class);
      if (psiClass == null) {
        return;
      }
      PsiElement lBrace = psiClass.getLBrace();
      PsiElement rBrace = psiClass.getRBrace();
      if (lBrace == null || rBrace == null || lBrace.getNextSibling() == null || rBrace.getPrevSibling() == null) {
        return;
      }

      CommentTracker tracker = new CommentTracker();
      String body = tracker.rangeText(lBrace.getNextSibling(), rBrace.getPrevSibling());
      PsiImplicitClass newClass = PsiElementFactory.getInstance(project).createImplicitClassFromText(body, psiClass);
      if (!(newClass.getContainingFile() instanceof PsiJavaFile dummyFile) ||
          dummyFile.getImportList() == null ||
          javaFile.getImportList() == null) {
        return;
      }
      //it is necessary to resolve accurately inside a new implicit class
      //collisions will be resolved after it
      dummyFile.getImportList().replace(javaFile.getImportList());
      PsiElement replaced = tracker.replace(psiClass, newClass);
      if (!(replaced instanceof PsiImplicitClass implicitClass)) {
        return;
      }

      tracker.insertCommentsBefore(implicitClass);

      cleanMainMethod(implicitClass);

      PsiFile replacedContainingFile = replaced.getContainingFile();
      if (replacedContainingFile == null) return;

      if (myConvertToIo && PsiUtil.isAvailable(JavaFeature.JAVA_LANG_IO, replacedContainingFile)) {
        convertToIOMethods(replacedContainingFile);
      }

      JavaCodeStyleManager.getInstance(project).optimizeImports(replacedContainingFile);
    }

    private static void convertToIOMethods(@NotNull PsiFile file) {
      if (!(file instanceof PsiJavaFile javaFile)) {
        return;
      }
      List<SmartPsiElementPointer<PsiMethodCallExpression>> systemOutPrints = new ArrayList<>();
      SmartPointerManager smartPointerManager = SmartPointerManager.getInstance(file.getProject());
      javaFile.accept(new JavaRecursiveElementWalkingVisitor() {
        @Override
        public void visitMethodCallExpression(@NotNull PsiMethodCallExpression expression) {
          if (MigrateToJavaLangIoInspection.isSystemOutPrintln(expression)) {
            systemOutPrints.add(smartPointerManager.createSmartPsiElementPointer(expression));
          }
          super.visitMethodCallExpression(expression);
        }
      });
      for (SmartPsiElementPointer<PsiMethodCallExpression> print : systemOutPrints) {
        PsiMethodCallExpression element = print.getElement();
        if (element == null) continue;
        MigrateToJavaLangIoInspection.replaceToIO(element);
      }
    }

    private static void cleanMainMethod(@NotNull PsiImplicitClass implicitClass) {
      PsiMethod mainMethod = PsiMethodUtil.findMainInClass(implicitClass);
      if (mainMethod == null) return;
      PsiModifierList modifierList = mainMethod.getModifierList();
      modifierList.setModifierProperty(PsiModifier.PUBLIC, false);
      modifierList.setModifierProperty(PsiModifier.PROTECTED, false);
      modifierList.setModifierProperty(PsiModifier.STATIC, false);

      PsiParameterList parameterList = mainMethod.getParameterList();
      if (parameterList.getParametersCount() == 0) return;
      PsiParameter parameter = parameterList.getParameters()[0];
      if (VariableAccessUtils.variableIsUsed(parameter, mainMethod)) return;
      CommentTracker ct = new CommentTracker();
      ct.deleteAndRestoreComments(parameter);
    }
  }
}