(zeppelin) branch master updated: [ZEPPELIN-6507] Return empty list from FileInterpreter.completion()

[gyeongtae]

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ParkGyeongTae pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/zeppelin.git


The following commit(s) were added to refs/heads/master by this push:
     new 560a808e3e [ZEPPELIN-6507] Return empty list from 
FileInterpreter.completion()
560a808e3e is described below

commit 560a808e3eab694654ab74c678ff1f1883c5c83c
Author: 김다은 (Daeun Kim) <150661115+dani1...@users.noreply.github.com>
AuthorDate: Sun Aug 9 21:43:22 2026 +0900

    [ZEPPELIN-6507] Return empty list from FileInterpreter.completion()
    
    ### What is this PR for?
    `FileInterpreter.completion()` returns `null` rather than an empty list. 
Per *Effective Java* Item 54, methods that return a collection should never 
return `null`, since it forces every caller to add a special-case null check.
    
    In practice this base implementation is not reached today: the only 
concrete subclass, `HDFSFileInterpreter`, overrides `completion()` with a real 
implementation. However, if a future `FileInterpreter` subclass omits that 
override, the `null` would propagate through the completion call chain, which 
does not perform null checks.
    
    This PR changes the base implementation to return `Collections.emptyList()` 
and adds a unit test that pins the contract.
    
    ### What type of PR is it?
    Improvement
    
    ### Todos
    * [x] - Return `Collections.emptyList()` from `FileInterpreter.completion()`
    * [x] - Add `testCompletionReturnsEmptyListInsteadOfNull` to 
`FileInterpreterTest`
    
    ### What is the Jira issue?
    * https://issues.apache.org/jira/browse/ZEPPELIN-6507
    
    ### How should this be tested?
    * `mvn test -pl file -Dtest=FileInterpreterTest`
    * `TestFileInterpreter`, the test double already present in 
`FileInterpreterTest`, does not override `completion()`, so the new test 
exercises the base implementation directly.
    * All 5 tests in `FileInterpreterTest` pass locally.
    
    ### Screenshots (if appropriate)
    N/A
    
    ### Questions:
    * Does the license files need to update? No
    * Is there breaking changes for older versions? No
    * Does this needs documentation? No
    
    Closes #5394 from dani1552/ZEPPELIN-6507.
    
    Signed-off-by: ParkGyeongTae <gyeong...@apache.org>
---
 .../main/java/org/apache/zeppelin/file/FileInterpreter.java |  3 ++-
 .../java/org/apache/zeppelin/file/FileInterpreterTest.java  | 13 +++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/file/src/main/java/org/apache/zeppelin/file/FileInterpreter.java 
b/file/src/main/java/org/apache/zeppelin/file/FileInterpreter.java
index 286d315ba8..50592cc5f3 100644
--- a/file/src/main/java/org/apache/zeppelin/file/FileInterpreter.java
+++ b/file/src/main/java/org/apache/zeppelin/file/FileInterpreter.java
@@ -24,6 +24,7 @@ import org.slf4j.LoggerFactory;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Properties;
@@ -167,6 +168,6 @@ public abstract class FileInterpreter extends Interpreter {
   @Override
   public List<InterpreterCompletion> completion(String buf, int cursor,
       InterpreterContext interpreterContext) {
-    return null;
+    return Collections.emptyList();
   }
 }
diff --git 
a/file/src/test/java/org/apache/zeppelin/file/FileInterpreterTest.java 
b/file/src/test/java/org/apache/zeppelin/file/FileInterpreterTest.java
index 6097d5fc59..01066a1fed 100644
--- a/file/src/test/java/org/apache/zeppelin/file/FileInterpreterTest.java
+++ b/file/src/test/java/org/apache/zeppelin/file/FileInterpreterTest.java
@@ -19,12 +19,15 @@
 package org.apache.zeppelin.file;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 
+import java.util.List;
 import java.util.Properties;
 
 import org.apache.zeppelin.interpreter.InterpreterException;
+import org.apache.zeppelin.interpreter.thrift.InterpreterCompletion;
 import org.junit.jupiter.api.Test;
 
 /**
@@ -178,4 +181,14 @@ class FileInterpreterTest {
     assertTrue(args.flags.contains('h'));
     assertFalse(args.flags.contains('-'));
   }
+
+  @Test
+  void testCompletionReturnsEmptyListInsteadOfNull() {
+    TestFileInterpreter interpreter = new TestFileInterpreter(new 
Properties());
+
+    List<InterpreterCompletion> completions = interpreter.completion("ls", 2, 
null);
+
+    assertNotNull(completions, "completion() should never return null");
+    assertTrue(completions.isEmpty(), "Default completion() should return an 
empty list");
+  }
 }