Search - add case insensitive support for regex queries. (elastic#59441)

(Backport)
Added case insensitive support for regex queries.
Forks a copy of Lucene’s RegexpQuery and RegExp from Lucene master.
This can be removed when 8.7 Lucene is released.

Closes elastic#59235

Author: markharwood

docs/reference/query-dsl/regexp-query.asciidoc

@@ -28,6 +28,7 @@ GET /_search
       "user.id": {
         "value": "k.*y",
         "flags": "ALL",
+        "case_insensitive": true,
         "max_determinized_states": 10000,
         "rewrite": "constant_score"
       }
@@ -67,6 +68,10 @@ provided. To improve performance, avoid using wildcard patterns, such as `.*` or
 valid values and more information, see <<regexp-optional-operators, Regular
 expression syntax>>.
 
+`case_insensitive`::
+(Optional, boolean) allows case insensitive matching of the regular expression
+value with the indexed field values when set to true. Setting to false is disallowed.
+
 `max_determinized_states`::
 +
 --

plugins/analysis-icu/src/main/java/org/elasticsearch/index/mapper/ICUCollationKeywordFieldMapper.java

@@ -146,7 +146,7 @@ public Query wildcardQuery(String value,
         }
 
         @Override
-        public Query regexpQuery(String value, int flags, int maxDeterminizedStates,
+        public Query regexpQuery(String value, int syntaxFlags, int matchFlags, int maxDeterminizedStates,
                                  MultiTermQuery.RewriteMethod method, QueryShardContext context) {
             throw new UnsupportedOperationException("[regexp] queries are not supported on [" + CONTENT_TYPE + "] fields.");
         }

plugins/analysis-icu/src/test/java/org/elasticsearch/index/mapper/CollationFieldTypeTests.java

@@ -91,7 +91,7 @@ public void testTermsQuery() {
     public void testRegexpQuery() {
         MappedFieldType ft = new CollationFieldType("field", DEFAULT_COLLATOR);
         UnsupportedOperationException e = expectThrows(UnsupportedOperationException.class,
-            () -> ft.regexpQuery("foo.*", 0, 10, null, randomMockShardContext()));
+            () -> ft.regexpQuery("foo.*", 0, 0, 10, null, randomMockShardContext()));
         assertEquals("[regexp] queries are not supported on [icu_collation_keyword] fields.", e.getMessage());
     }
 

server/build.gradle

@@ -333,5 +333,8 @@ tasks.named("dependencyLicenses").configure {
 tasks.named("licenseHeaders").configure {
     // Ignore our vendored version of Google Guice
     excludes << 'org/elasticsearch/common/inject/**/*'
+    // Ignore temporary copies of impending 8.7 Lucene classes
+    excludes << 'org/apache/lucene/search/RegExp87*'
+    excludes << 'org/apache/lucene/search/RegexpQuery87*'
     excludes << 'org/elasticsearch/client/documentation/placeholder.txt'
-}
+}