[fix](view) ALTER VIEW definition not synced to follower FE when COMMENT is specified

fe/fe-core/src/main/java/org/apache/doris/alter/Alter.java

@@ -902,7 +902,8 @@ public void replayModifyViewDef(AlterViewInfo alterViewInfo) throws MetaNotFound
             String viewName = view.getName();
             if (comment != null) {
                 view.setComment(comment);
-            } else {
+            }
+            if (!Strings.isNullOrEmpty(inlineViewDef)) {
                 view.setInlineViewDefWithSessionVariables(inlineViewDef, alterViewInfo.getSessionVariables());
                 view.setNewFullSchema(newFullSchema);
             }

fe/fe-core/src/test/java/org/apache/doris/alter/ReplayModifyViewDefTest.java

@@ -0,0 +1,196 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.apache.doris.alter;
+
+import org.apache.doris.catalog.Column;
+import org.apache.doris.catalog.Database;
+import org.apache.doris.catalog.Env;
+import org.apache.doris.catalog.PrimitiveType;
+import org.apache.doris.catalog.View;
+import org.apache.doris.nereids.parser.NereidsParser;
+import org.apache.doris.nereids.trees.plans.commands.CreateDatabaseCommand;
+import org.apache.doris.nereids.trees.plans.commands.CreateTableCommand;
+import org.apache.doris.nereids.trees.plans.commands.CreateViewCommand;
+import org.apache.doris.nereids.trees.plans.logical.LogicalPlan;
+import org.apache.doris.persist.AlterViewInfo;
+import org.apache.doris.qe.ConnectContext;
+import org.apache.doris.qe.StmtExecutor;
+import org.apache.doris.utframe.UtFrameUtils;
+
+import com.google.common.collect.Lists;
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.File;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.UUID;
+
+/**
+ * Unit tests for {@link Alter#replayModifyViewDef}.
+ *
+ * Covers three replay scenarios:
+ * 1. Replay a full view definition change (new SQL + new schema).
+ * 2. Replay a comment-only change (inlineViewDef is empty / null → def must not change).
+ * 3. Replay with both a new definition and a new comment simultaneously.
+ */
+public class ReplayModifyViewDefTest {
+
+    private static final String RUNNING_DIR =
+            "fe/mocked/ReplayModifyViewDefTest/" + UUID.randomUUID() + "/";
+
+    private static ConnectContext connectContext;
+
+    // ──────────────────────────────────────────────────────────────────────────
+    // Setup / Teardown
+    // ──────────────────────────────────────────────────────────────────────────
+
+    @BeforeClass
+    public static void beforeClass() throws Exception {
+        UtFrameUtils.createDorisCluster(RUNNING_DIR);
+        connectContext = UtFrameUtils.createDefaultCtx();
+        connectContext.getSessionVariable().setDisableNereidsRules("PRUNE_EMPTY_PARTITION");
+
+        NereidsParser parser = new NereidsParser();
+
+        // create database
+        String createDb = "create database test_replay_view;";
+        LogicalPlan plan = parser.parseSingle(createDb);
+        if (plan instanceof CreateDatabaseCommand) {
+            ((CreateDatabaseCommand) plan).run(connectContext, new StmtExecutor(connectContext, createDb));
+        }
+
+        // create table
+        String createTbl = "create table test_replay_view.tbl1(k1 int, k2 int, v1 int)"
+                + " duplicate key(k1) distributed by hash(k1) buckets 1"
+                + " properties('replication_num' = '1');";
+        plan = parser.parseSingle(createTbl);
+        if (plan instanceof CreateTableCommand) {
+            ((CreateTableCommand) plan).run(connectContext, new StmtExecutor(connectContext, createTbl));
+        }
+
+        // create initial view
+        String createView = "create view test_replay_view.v1 as select k1, k2 from test_replay_view.tbl1;";
+        plan = parser.parseSingle(createView);
+        if (plan instanceof CreateViewCommand) {
+            ((CreateViewCommand) plan).run(connectContext, new StmtExecutor(connectContext, createView));
+        }
+    }
+
+    @AfterClass
+    public static void tearDown() {
+        new File(RUNNING_DIR).delete();
+    }
+
+    // ──────────────────────────────────────────────────────────────────────────
+    // Helpers
+    // ──────────────────────────────────────────────────────────────────────────
+
+    private static View getView(String viewName) throws Exception {
+        Database db = Env.getCurrentInternalCatalog().getDbOrDdlException("test_replay_view");
+        return (View) db.getTableOrDdlException(viewName);
+    }
+
+    private static long getDbId() throws Exception {
+        return Env.getCurrentInternalCatalog().getDbOrDdlException("test_replay_view").getId();
+    }
+
+    // ──────────────────────────────────────────────────────────────────────────
+    // Tests
+    // ──────────────────────────────────────────────────────────────────────────
+
+    /**
+     * Replay a full definition change.
+     * After replay the view's inlineViewDef and full-schema must reflect the new values.
+     */
+    @Test
+    public void testReplayModifyViewDefWithNewDef() throws Exception {
+        View view = getView("v1");
+        long dbId = getDbId();
+        long tableId = view.getId();
+
+        String newDef = "select k1, v1 from test_replay_view.tbl1 where k1 > 0";
+        List<Column> newSchema = Lists.newArrayList(
+                new Column("k1", PrimitiveType.INT),
+                new Column("v1", PrimitiveType.INT));
+
+        AlterViewInfo info = new AlterViewInfo(dbId, tableId, newDef, newSchema,
+                new HashMap<>(), null);
+
+        Env.getCurrentEnv().getAlterInstance().replayModifyViewDef(info);
+
+        View updated = getView("v1");
+        Assert.assertEquals(newDef, updated.getInlineViewDef());
+        Assert.assertEquals(2, updated.getFullSchema().size());
+        Assert.assertNotNull(updated.getColumn("k1"));
+        Assert.assertNotNull(updated.getColumn("v1"));
+        Assert.assertNull(updated.getColumn("k2"));
+    }
+
+    /**
+     * Replay a comment-only change (inlineViewDef is null).
+     * The view definition must remain unchanged; only the comment is updated.
+     */
+    @Test
+    public void testReplayModifyViewDefCommentOnly() throws Exception {
+        // First bring v1 back to a known state with two columns.
+        View view = getView("v1");
+        long dbId = getDbId();
+        long tableId = view.getId();
+        String originalDef = view.getInlineViewDef();
+
+        AlterViewInfo info = new AlterViewInfo(dbId, tableId, null,
+                Collections.emptyList(), new HashMap<>(), "my comment");
+
+        Env.getCurrentEnv().getAlterInstance().replayModifyViewDef(info);
+
+        View updated = getView("v1");
+        // Definition must not change.
+        Assert.assertEquals(originalDef, updated.getInlineViewDef());
+        // Comment must be set.
+        Assert.assertEquals("my comment", updated.getComment());
+    }
+
+    /**
+     * Replay with both a new definition and a comment.
+     * Both the def/schema and the comment must be updated.
+     */
+    @Test
+    public void testReplayModifyViewDefWithDefAndComment() throws Exception {
+        View view = getView("v1");
+        long dbId = getDbId();
+        long tableId = view.getId();
+
+        String newDef = "select k2 from test_replay_view.tbl1";
+        List<Column> newSchema = Lists.newArrayList(new Column("k2", PrimitiveType.INT));
+
+        AlterViewInfo info = new AlterViewInfo(dbId, tableId, newDef, newSchema,
+                new HashMap<>(), "updated comment");
+
+        Env.getCurrentEnv().getAlterInstance().replayModifyViewDef(info);
+
+        View updated = getView("v1");
+        Assert.assertEquals(newDef, updated.getInlineViewDef());
+        Assert.assertEquals(1, updated.getFullSchema().size());
+        Assert.assertNotNull(updated.getColumn("k2"));
+        Assert.assertEquals("updated comment", updated.getComment());
+    }
+}