Allow duplicate function signatures when matching with generic candidates

Author: pramodsatya

presto-main-base/src/main/java/com/facebook/presto/metadata/FunctionSignatureMatcher.java

@@ -71,7 +71,7 @@ public Optional<Signature> match(Collection<? extends SqlFunction> candidates, L
                 .filter(function -> !function.getSignature().getTypeVariableConstraints().isEmpty())
                 .collect(Collectors.toList());
 
-        match = matchFunctionExact(genericCandidates, parameterTypes);
+        match = matchFunctionGeneric(genericCandidates, parameterTypes);
         if (match.isPresent()) {
             return match;
         }
@@ -91,6 +91,28 @@ private Optional<Signature> matchFunctionExact(List<SqlFunction> candidates, Lis
         return matchFunction(candidates, actualParameters, false);
     }
 
+    private Optional<Signature> matchFunctionGeneric(List<SqlFunction> candidates, List<TypeSignatureProvider> actualParameters)
+    {
+        List<ApplicableFunction> applicableFunctions = identifyApplicableFunctions(candidates, actualParameters, false);
+        if (applicableFunctions.isEmpty()) {
+            return Optional.empty();
+        }
+
+        if (applicableFunctions.size() == 1) {
+            return Optional.of(getOnlyElement(applicableFunctions).getBoundSignature());
+        }
+
+        List<Signature> deduplicatedSignatures = applicableFunctions.stream()
+                .map(applicableFunction -> applicableFunction.boundSignature)
+                .distinct()
+                .collect(toImmutableList());
+        if (deduplicatedSignatures.size() == 1) {
+            return Optional.of(getOnlyElement(deduplicatedSignatures));
+        }
+
+        throw new PrestoException(AMBIGUOUS_FUNCTION_CALL, getErrorMessage(applicableFunctions));
+    }
+
     private Optional<Signature> matchFunctionWithCoercion(Collection<? extends SqlFunction> candidates, List<TypeSignatureProvider> actualParameters)
     {
         return matchFunction(candidates, actualParameters, true);
@@ -112,6 +134,11 @@ private Optional<Signature> matchFunction(Collection<? extends SqlFunction> cand
             return Optional.of(getOnlyElement(applicableFunctions).getBoundSignature());
         }
 
+        throw new PrestoException(AMBIGUOUS_FUNCTION_CALL, getErrorMessage(applicableFunctions));
+    }
+
+    private String getErrorMessage(List<ApplicableFunction> applicableFunctions)
+    {
         StringBuilder errorMessageBuilder = new StringBuilder();
         errorMessageBuilder.append("Could not choose a best candidate operator. Explicit type casts must be added.\n");
         errorMessageBuilder.append("Candidates are:\n");
@@ -120,7 +147,8 @@ private Optional<Signature> matchFunction(Collection<? extends SqlFunction> cand
             errorMessageBuilder.append(function.getBoundSignature().toString());
             errorMessageBuilder.append("\n");
         }
-        throw new PrestoException(AMBIGUOUS_FUNCTION_CALL, errorMessageBuilder.toString());
+
+        return errorMessageBuilder.toString();
     }
 
     private List<ApplicableFunction> identifyApplicableFunctions(Collection<? extends SqlFunction> candidates, List<TypeSignatureProvider> actualParameters, boolean allowCoercion)

presto-native-sidecar-plugin/src/test/java/com/facebook/presto/sidecar/TestNativeSidecarPlugin.java

@@ -334,6 +334,20 @@ public void testApproxPercentile()
         }
     }
 
+    @Test
+    public void testMapSubset()
+    {
+        assertQuery("select m[1], m[3] from (select map_subset(map(array[1,2,3,4], array['a', 'b', 'c', 'd']), array[1,3,10]) m)", "select 'a', 'c'");
+        assertQuery("select m['p'], m['r'] from (select map_subset(map(array['p', 'q', 'r', 's'], array['a', 'b', 'c', 'd']), array['p', 'r', 'z']) m)", "select 'a', 'c'");
+        assertQuery("select m[true], m[false] from (select map_subset(map(array[false, true], array['a', 'z']), array[true, false]) m)", "select 'z', 'a'");
+        assertQuery("select m[DATE '2015-01-01'], m[DATE '2015-01-13'] from (select map_subset(" +
+                "map(array[DATE '2015-01-01', DATE '2015-02-13', DATE '2015-01-13', DATE '2015-05-15'], array['a', 'b', 'c', 'd']), " +
+                "array[DATE '2015-01-01', DATE '2015-01-13', DATE '2015-06-15']) m)", "select 'a', 'c'");
+        assertQuery("select m[TIMESTAMP '2021-01-02 09:04:05.321'] from (select map_subset(" +
+                "map(array[TIMESTAMP '2021-01-02 09:04:05.321', TIMESTAMP '2022-12-22 10:07:08.456'], array['a', 'b']), " +
+                "array[TIMESTAMP '2021-01-02 09:04:05.321', TIMESTAMP '2022-12-22 10:07:09.246']) m)", "select 'a'");
+    }
+
     @Test
     public void testInformationSchemaTables()
     {