[java] IDEA-263507 Line join silently changes semantics for nested ifs

GitOrigin-RevId: 59502372bb306221a601ee1aa0991a8092eb7335

java/java-impl/src/com/intellij/codeInsight/editorActions/BlockJoinLinesHandler.java

@@ -56,8 +56,22 @@ public class BlockJoinLinesHandler implements JoinLinesHandlerDelegate {
       if (foundStatement != null) return -1;
       foundStatement = element;
     }
+    if (foundStatement == null) return -1;
+    PsiElement parent = codeBlock.getParent();
+    if (foundStatement instanceof PsiIfStatement && parent instanceof PsiBlockStatement) {
+      PsiElement grandParent = parent.getParent();
+      if (grandParent instanceof PsiIfStatement &&
+          ((PsiIfStatement)grandParent).getThenBranch() == parent &&
+          ((PsiIfStatement)grandParent).getElseBranch() != null) {
+        /*
+         like "if(...) {if(...){...}} else {...}"
+         unwrapping the braces of outer 'if' then-branch will cause semantics change
+         */
+        return -1;
+      }
+    }
     try {
-      final PsiElement newStatement = codeBlock.getParent().replace(foundStatement);
+      final PsiElement newStatement = parent.replace(foundStatement);
 
       return newStatement.getTextRange().getStartOffset();
     }

java/java-tests/testData/codeInsight/joinLines/UnwrapCodeBlockIfElse.java

@@ -0,0 +1,11 @@
+class C {
+  private static void fn(boolean condA, boolean condB) {
+    if (condA) {<caret>
+      if (condB) {
+        System.out.println("condA && condB");
+      }
+    } else {
+      System.out.println("!condA");
+    }
+  }
+}

java/java-tests/testData/codeInsight/joinLines/UnwrapCodeBlockIfElse_after.java

@@ -0,0 +1,10 @@
+class C {
+  private static void fn(boolean condA, boolean condB) {
+    if (condA) { if (condB) {
+        System.out.println("condA && condB");
+      }
+    } else {
+      System.out.println("!condA");
+    }
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/JoinLinesTest.java

@@ -195,7 +195,8 @@ public class JoinLinesTest extends LightJavaCodeInsightTestCase {
       settings.IF_BRACE_FORCE = old;
     }
   }
-
+  
+  public void testUnwrapCodeBlockIfElse() { doTest(); }
   public void testAssignmentExpression() { doTest(); }
   public void testAssignmentExpression2() { doTest(); }
   public void testAssignmentExpressionPrecedence() { doTest(); }