Require [articles] setting in elision filter (#43083)

We should throw an exception at construction time if a list of
articles is not provided, otherwise we can get random NPEs during
indexing.

Relates to #43002

Author: romseygeek

docs/reference/analysis/tokenfilters/elision-tokenfilter.asciidoc

@@ -4,8 +4,9 @@
 A token filter which removes elisions. For example, "l'avion" (the
 plane) will tokenized as "avion" (plane).
 
-Accepts `articles` parameter which is a set of stop words articles. Also accepts
-`articles_case`, which indicates whether the filter treats those articles as
+Requires either an `articles` parameter which is a set of stop word articles, or
+`articles_path` which points to a text file containing the stop set. Also optionally
+accepts `articles_case`, which indicates whether the filter treats those articles as
 case sensitive.
 
 For example:

modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/CommonAnalysisPlugin.java

@@ -239,7 +239,7 @@ public Map<String, AnalysisProvider<TokenFilterFactory>> getTokenFilters() {
         filters.put("dutch_stem", DutchStemTokenFilterFactory::new);
         filters.put("edge_ngram", EdgeNGramTokenFilterFactory::new);
         filters.put("edgeNGram", EdgeNGramTokenFilterFactory::new);
-        filters.put("elision", ElisionTokenFilterFactory::new);
+        filters.put("elision", requiresAnalysisSettings(ElisionTokenFilterFactory::new));
         filters.put("fingerprint", FingerprintTokenFilterFactory::new);
         filters.put("flatten_graph", FlattenGraphTokenFilterFactory::new);
         filters.put("french_stem", FrenchStemTokenFilterFactory::new);

modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/ElisionTokenFilterFactory.java

@@ -36,6 +36,9 @@ public class ElisionTokenFilterFactory extends AbstractTokenFilterFactory implem
     ElisionTokenFilterFactory(IndexSettings indexSettings, Environment env, String name, Settings settings) {
         super(indexSettings, name, settings);
         this.articles = Analysis.parseArticles(env, settings);
+        if (this.articles == null) {
+            throw new IllegalArgumentException("elision filter requires [articles] or [articles_path] setting");
+        }
     }
 
     @Override

modules/analysis-common/src/test/java/org/elasticsearch/analysis/common/ElisionFilterFactoryTests.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch 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.elasticsearch.analysis.common;
+
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.index.analysis.AnalysisTestsHelper;
+import org.elasticsearch.test.ESTokenStreamTestCase;
+
+import java.io.IOException;
+
+public class ElisionFilterFactoryTests extends ESTokenStreamTestCase {
+
+    public void testElisionFilterWithNoArticles() throws IOException {
+        Settings settings = Settings.builder()
+            .put("index.analysis.filter.elision.type", "elision")
+            .put(Environment.PATH_HOME_SETTING.getKey(), createTempDir().toString())
+            .build();
+
+        IllegalArgumentException e = expectThrows(IllegalArgumentException.class,
+            () -> AnalysisTestsHelper.createTestAnalysisFromSettings(settings, new CommonAnalysisPlugin()));
+
+        assertEquals("elision filter requires [articles] or [articles_path] setting", e.getMessage());
+    }
+
+}

modules/analysis-common/src/test/resources/rest-api-spec/test/analysis-common/40_token_filters.yml

@@ -587,6 +587,20 @@
     - length: { tokens: 1 }
     - match:  { tokens.0.token: avion }
 
+    - do:
+        catch: bad_request
+        indices.create:
+          index: test2
+          body:
+            settings:
+              analysis:
+                filter:
+                  my_elision:
+                    type: elision
+    - match: { status: 400 }
+    - match: { error.type: illegal_argument_exception }
+    - match: { error.reason: "elision filter requires [articles] or [articles_path] setting" }
+
 ---
 "stemmer":
     - do: