[java-core] JavaPsiSingleFileSourceUtil moved to codeserver.core

GitOrigin-RevId: 2368062535cd331747a871d22f405e4683ae8bd6

java/codeserver/core/src/com/intellij/java/codeserver/core/JavaPsiSingleFileSourceUtil.java

@@ -0,0 +1,44 @@
+// 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.java.codeserver.core;
+
+import com.intellij.openapi.vfs.VfsUtilCore;
+import com.intellij.openapi.vfs.VirtualFile;
+import com.intellij.psi.*;
+import com.intellij.psi.impl.PsiFileEx;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.IOException;
+
+/**
+ * Utilities related to single-file Java programs (JEP 330)
+ */
+public final class JavaPsiSingleFileSourceUtil {
+  /**
+   * @return true if file correspond to the shebang script
+   */
+  public static boolean isJavaHashBangScript(@NotNull PsiFile containingFile) {
+    if (!(containingFile instanceof PsiJavaFile)) return false;
+    if (containingFile instanceof PsiFileEx && !((PsiFileEx)containingFile).isContentsLoaded()) {
+      VirtualFile vFile = containingFile.getVirtualFile();
+      if (vFile.isInLocalFileSystem()) {
+        try {
+          // don't build PSI when not yet loaded -> time for scanning scope from 18 seconds to 8 seconds on IntelliJ project
+          return VfsUtilCore.loadText(vFile, 5).startsWith("#!");
+        }
+        catch (IOException e) {
+          return false;
+        }
+      }
+    }
+    PsiElement firstChild = containingFile.getFirstChild();
+    if (firstChild instanceof PsiImportList && firstChild.getTextLength() == 0) {
+      PsiElement sibling = firstChild.getNextSibling();
+      if (sibling instanceof PsiClass) {
+        firstChild = sibling.getFirstChild();
+      }
+    }
+    return firstChild instanceof PsiComment &&
+           ((PsiComment)firstChild).getTokenType() == JavaTokenType.END_OF_LINE_COMMENT &&
+           firstChild.getText().startsWith("#!");
+  }
+}