Improve test coverage and update doc

Author: s4ch1n

docs/en/sql-reference/sql-statements/cluster-management/plugin/INSTALL_PLUGIN.md

@@ -16,9 +16,11 @@ This operation requires the SYSTEM-level PLUGIN privilege. You can follow the in
 ## Syntax
 
 ```sql
-INSTALL PLUGIN FROM [source] [PROPERTIES ("key"="value", ...)]
+INSTALL PLUGIN [IF NOT EXISTS] FROM [source] [PROPERTIES ("key"="value", ...)]
 ```
 
+**IF NOT EXISTS**: If specified, the statement succeeds silently when the plugin is already installed instead of returning an error.
+
 3 types of sources are supported:
 
 ```plain text
@@ -54,3 +56,9 @@ PROPERTIES supports setting some configurations of plugins, such as setting the
     ```sql
     INSTALL PLUGIN FROM "http://mywebsite.com/plugin.zip" PROPERTIES("md5sum" = "73877f6029216f4314d712086a146570");
     ```
+
+5. Install a plugin if it is not already installed:
+
+    ```sql
+    INSTALL PLUGIN IF NOT EXISTS FROM "/home/users/starrocks/auditdemo.zip";
+    ```

docs/en/sql-reference/sql-statements/cluster-management/plugin/UNINSTALL_PLUGIN.md

@@ -16,9 +16,11 @@ This operation requires the SYSTEM-level PLUGIN privilege. You can follow the in
 ## Syntax
 
 ```SQL
-UNINSTALL PLUGIN <plugin_name>
+UNINSTALL PLUGIN [IF EXISTS] <plugin_name>
 ```
 
+**IF EXISTS**: If specified, the statement succeeds silently when the plugin does not exist instead of returning an error.
+
 plugin_name can be viewed through SHOW PLUGINS command
 
 Only non-builtin plugins can be uninstalled.
@@ -30,3 +32,9 @@ Only non-builtin plugins can be uninstalled.
     ```SQL
     UNINSTALL PLUGIN auditdemo;
     ```
+
+2. Uninstall a plugin if it exists:
+
+    ```SQL
+    UNINSTALL PLUGIN IF EXISTS auditdemo;
+    ```

fe/fe-core/src/test/java/com/starrocks/analysis/InstallPluginStmtTest.java

@@ -74,4 +74,19 @@ public void testUninstallPluginWithoutIfExistsDefaultsFalse() {
         UninstallPluginStmt stmt = (UninstallPluginStmt) stmts.get(0);
         Assertions.assertFalse(stmt.isIfExists());
     }
+
+    @Test
+    public void testInstallPluginConstructorDefaultsIfNotExistsFalse() {
+        Map<String, String> props = Maps.newHashMap();
+        InstallPluginStmt stmt = new InstallPluginStmt("http://test/plugin.zip", props);
+        Assertions.assertFalse(stmt.isIfNotExists());
+        Assertions.assertEquals("http://test/plugin.zip", stmt.getPluginPath());
+    }
+
+    @Test
+    public void testUninstallPluginConstructorDefaultsIfExistsFalse() {
+        UninstallPluginStmt stmt = new UninstallPluginStmt("my_plugin");
+        Assertions.assertFalse(stmt.isIfExists());
+        Assertions.assertEquals("my_plugin", stmt.getPluginName());
+    }
 }

fe/fe-core/src/test/java/com/starrocks/plugin/PluginMgrTest.java

@@ -34,20 +34,32 @@
 
 package com.starrocks.plugin;
 
+import com.google.common.collect.Maps;
 import com.starrocks.common.Config;
 import com.starrocks.common.util.DigitalVersion;
+import com.starrocks.persist.EditLog;
+import com.starrocks.persist.UninstallPluginLog;
+import com.starrocks.persist.WALApplier;
 import com.starrocks.plugin.PluginInfo.PluginType;
 import com.starrocks.server.GlobalStateMgr;
+import com.starrocks.sql.ast.InstallPluginStmt;
+import com.starrocks.sql.ast.UninstallPluginStmt;
+import com.starrocks.sql.parser.NodePosition;
 import com.starrocks.utframe.UtFrameUtils;
+import mockit.Mock;
+import mockit.MockUp;
 import org.apache.commons.io.FileUtils;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import java.io.IOException;
 import java.nio.file.Files;
+import java.util.Map;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class PluginMgrTest {
@@ -89,4 +101,53 @@ public void testLoadPluginFail() {
             assert false;
         }
     }
+
+    @Test
+    public void testInstallPluginIfNotExistsIdempotent() throws Exception {
+        String pluginName = "idempotent_install_plugin";
+        PluginInfo pluginInfo = new PluginInfo(pluginName, PluginType.AUDIT, "test");
+
+        PluginMgr pluginMgr = new PluginMgr();
+        pluginMgr.replayLoadDynamicPlugin(pluginInfo);
+
+        new MockUp<DynamicPluginLoader>() {
+            @Mock
+            public PluginInfo getPluginInfo() throws IOException {
+                return pluginInfo;
+            }
+        };
+
+        Map<String, String> props = Maps.newHashMap();
+        InstallPluginStmt stmt = new InstallPluginStmt("http://dummy/test.zip", props, true, NodePosition.ZERO);
+        PluginInfo result = pluginMgr.installPlugin(stmt);
+        assertNull(result);
+    }
+
+    @Test
+    public void testUninstallPluginIfExistsIdempotent() {
+        PluginMgr pluginMgr = new PluginMgr();
+        UninstallPluginStmt stmt = new UninstallPluginStmt("nonexistent_plugin", true, NodePosition.ZERO);
+        assertDoesNotThrow(() -> pluginMgr.uninstallPluginFromStmt(stmt));
+    }
+
+    @Test
+    public void testUninstallPluginFromStmtNormal() throws Exception {
+        String pluginName = "normal_uninstall_plugin";
+        PluginInfo pluginInfo = new PluginInfo(pluginName, PluginType.AUDIT, "test");
+
+        PluginMgr pluginMgr = new PluginMgr();
+        pluginMgr.replayLoadDynamicPlugin(pluginInfo);
+
+        new MockUp<EditLog>() {
+            @Mock
+            public void logUninstallPlugin(UninstallPluginLog log, WALApplier walApplier) {
+                walApplier.apply(log);
+            }
+        };
+
+        UninstallPluginStmt stmt = new UninstallPluginStmt(pluginName);
+        pluginMgr.uninstallPluginFromStmt(stmt);
+        assertFalse(pluginMgr.getAllDynamicPluginInfo()
+                .stream().anyMatch(p -> p.getName().equals(pluginName)));
+    }
 }