[Cleanup] utilize the same helper function

Originally when implementing the fix the historical comment caused concern about
potential breaking changes.

But after discussion, we decided it is more clear to consolidate the helper functions.

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>

src/plugins/data/common/opensearch_query/opensearch_query/filter_matches_index.test.ts

@@ -66,4 +66,18 @@ describe('filterMatchesIndex', () => {
 
     expect(filterMatchesIndex(filter, indexPattern)).toBe(true);
   });
+
+  it('should return false if the custom filter is a different index id', () => {
+    const filter = { meta: { index: 'foo', key: 'bar', type: 'custom' } } as Filter;
+    const indexPattern = { id: 'bar', fields: [{ name: 'foo' }] } as IIndexPattern;
+
+    expect(filterMatchesIndex(filter, indexPattern)).toBe(false);
+  });
+
+  it('should return true if the custom filter is the same index id', () => {
+    const filter = { meta: { index: 'foo', key: 'bar', type: 'custom' } } as Filter;
+    const indexPattern = { id: 'foo', fields: [{ name: 'barf' }] } as IIndexPattern;
+
+    expect(filterMatchesIndex(filter, indexPattern)).toBe(true);
+  });
 });

src/plugins/data/common/opensearch_query/opensearch_query/filter_matches_index.ts

@@ -31,14 +31,14 @@
 import { IIndexPattern, IFieldType } from '../../index_patterns';
 import { Filter } from '../filters';
 
-/*
- * TODO: We should base this on something better than `filter.meta.key`. We should probably modify
- * this to check if `filter.meta.index` matches `indexPattern.id` instead, but that's a breaking
- * change.
- */
 export function filterMatchesIndex(filter: Filter, indexPattern?: IIndexPattern | null) {
   if (!filter.meta?.key || !indexPattern) {
     return true;
   }
+
+  if (filter.meta?.type === 'custom') {
+    return filter.meta.index === indexPattern.id;
+  }
+
   return indexPattern.fields.some((field: IFieldType) => field.name === filter.meta.key);
 }

src/plugins/data/common/opensearch_query/opensearch_query/from_filters.ts

@@ -34,7 +34,6 @@ import { filterMatchesIndex } from './filter_matches_index';
 import { Filter, cleanFilter, isFilterDisabled } from '../filters';
 import { IIndexPattern } from '../../index_patterns';
 import { handleNestedFilter } from './handle_nested_filter';
-import { customFilterMatchesIndex } from './custom_filter_matches_index';
 
 /**
  * Create a filter that can be reversed for filters with negate set
@@ -77,10 +76,7 @@ export const buildQueryFromFilters = (
     return filters
       .filter(filterNegate(negate))
       .filter(
-        (filter) =>
-          !ignoreFilterIfFieldNotInIndex ||
-          filterMatchesIndex(filter, indexPattern) ||
-          customFilterMatchesIndex(filter, indexPattern)
+        (filter) => !ignoreFilterIfFieldNotInIndex || filterMatchesIndex(filter, indexPattern)
       )
       .map((filter) => {
         return migrateFilter(filter, indexPattern);