chore (isthmus): fix regression

Author: ZorinAnton

isthmus/src/main/java/io/substrait/isthmus/expression/FunctionConverter.java

@@ -25,7 +25,6 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
-import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -129,8 +128,7 @@ public FunctionConverter(
             .collect(
                 Multimaps.toMultimap(
                     FunctionMappings.Sig::name, Function.identity(), ArrayListMultimap::create));
-    IdentityHashMap<SqlOperator, FunctionFinder> matcherMap =
-        new IdentityHashMap<SqlOperator, FunctionFinder>();
+    Map<SqlOperator, FunctionFinder> matcherMap = new HashMap<>();
     for (String key : nameToFn.keySet()) {
       Collection<Sig> sigs = calciteOperators.get(key);
       if (sigs.isEmpty()) {

isthmus/src/test/java/io/substrait/isthmus/UdfSqlSubstraitTest.java

@@ -23,13 +23,13 @@ void customUdfTest() throws Exception {
             "CREATE TABLE t(x VARCHAR NOT NULL)");
 
     assertSqlSubstraitRelRoundTripWorkaroundOptimizer(
-        "SELECT regexp_extract(x, 'ab') from t", catalogReader);
+        "SELECT regexp_extract_custom(x, 'ab') from t", catalogReader);
     assertSqlSubstraitRelRoundTripWorkaroundOptimizer(
         "SELECT format_text('UPPER', x) FROM t", catalogReader);
     assertSqlSubstraitRelRoundTripWorkaroundOptimizer(
         "SELECT system_property_get(x) FROM t", catalogReader);
     assertSqlSubstraitRelRoundTripWorkaroundOptimizer(
-        "SELECT safe_divide(10,0) FROM t", catalogReader);
+        "SELECT safe_divide_custom(10,0) FROM t", catalogReader);
   }
 
   private static SimpleExtension.ExtensionCollection loadExtensions(

isthmus/src/test/resources/extensions/scalar_functions_custom.yaml

@@ -2,7 +2,7 @@
 ---
 urn: extension:substrait:functions_custom
 scalar_functions:
-  - name: "regexp_extract"
+  - name: "regexp_extract_custom"
     impls:
       - args:
           - name: "text"
@@ -33,7 +33,7 @@ scalar_functions:
         return: string?
         nullability: DECLARED_OUTPUT
 
-  - name: "safe_divide"
+  - name: "safe_divide_custom"
     description: "Performs division, returning NULL if the denominator is zero."
     impls:
       - args: