Fix Queryable-to-Enumerable overload mapping logic

src/libraries/System.Linq.Queryable/src/System/Linq/EnumerableRewriter.cs

@@ -255,25 +255,83 @@ protected override Expression VisitConstant(ConstantExpression c)
         }
 
         private static ILookup<string, MethodInfo>? s_seqMethods;
-        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060:MakeGenericMethod",
-            Justification = "Enumerable methods don't have trim annotations.")]
         private static MethodInfo FindEnumerableMethodForQueryable(string name, ReadOnlyCollection<Expression> args, params Type[]? typeArgs)
         {
-            if (s_seqMethods == null)
+            s_seqMethods ??= GetEnumerableStaticMethods(typeof(Enumerable)).ToLookup(m => m.Name);
+
+            MethodInfo[] matchingMethods = s_seqMethods[name]
+                .Where(m => ArgsMatch(m, args, typeArgs))
+                .Select(ApplyTypeArgs)
+                .ToArray();
+
+            Debug.Assert(matchingMethods.Length > 0, "All static methods with arguments on Queryable have equivalents on Enumerable.");
+
+            if (matchingMethods.Length > 1)
             {
-                s_seqMethods = GetEnumerableStaticMethods(typeof(Enumerable)).ToLookup(m => m.Name);
+                return DisambiguateMatches(matchingMethods);
             }
-            MethodInfo? mi = s_seqMethods[name].FirstOrDefault(m => ArgsMatch(m, args, typeArgs));
-            Debug.Assert(mi != null, "All static methods with arguments on Queryable have equivalents on Enumerable.");
-            if (typeArgs != null)
-                return mi.MakeGenericMethod(typeArgs);
-            return mi;
+
+            return matchingMethods[0];
 
             [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2070:UnrecognizedReflectionPattern",
                 Justification = "This method is intentionally hiding the Enumerable type from the trimmer so it doesn't preserve all Enumerable's methods. " +
                 "This is safe because all Queryable methods have a DynamicDependency to the corresponding Enumerable method.")]
             static MethodInfo[] GetEnumerableStaticMethods(Type type) =>
                 type.GetMethods(BindingFlags.Public | BindingFlags.Static);
+
+            [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2060:MakeGenericMethod",
+                Justification = "Enumerable methods don't have trim annotations.")]
+            MethodInfo ApplyTypeArgs(MethodInfo methodInfo) => typeArgs == null ? methodInfo : methodInfo.MakeGenericMethod(typeArgs);
+
+            // In certain cases, there might be ambiguities when resolving matching overloads, for example between
+            //   1. FirstOrDefault<object>(IEnumerable<object> source, Func<object, bool> predicate) and
+            //   2. FirstOrDefault<object>(IEnumerable<object> source, object defaultvalue).
+            // In such cases we disambiguate by picking a method with the most derived signature.
+            static MethodInfo DisambiguateMatches(MethodInfo[] matchingMethods)
+            {
+                Debug.Assert(matchingMethods.Length > 1);
+                ParameterInfo[][] parameters = matchingMethods.Select(m => m.GetParameters()).ToArray();
+
+                // `IsLessDerivedThan` defines a partial order on method signatures; pick a maximal element using that order.
+                // It is assumed that `matchingMethods` is a small array, so a naive quadratic search is probably better than
+                // doing some variant of topological sorting.
+
+                for (int i = 0; i < matchingMethods.Length; i++)
+                {
+                    bool foundDerivedMethodSignature = false;
+                    for (int j = 0; j < matchingMethods.Length; j++)
+                    {
+                        if (i != j && IsLessDerivedThan(parameters[i], parameters[j]))
+                        {
+                            foundDerivedMethodSignature = true;
+                            break;
+                        }
+                    }
+
+                    if (!foundDerivedMethodSignature)
+                    {
+                        // Found a maximal element
+                        return matchingMethods[i];
+                    }
+                }
+
+                Debug.Fail("Search should have found a maximal element");
+                throw new Exception();
+
+                static bool IsLessDerivedThan(ParameterInfo[] params1, ParameterInfo[] params2)
+                {
+                    Debug.Assert(params1.Length == params2.Length);
+                    for (int i = 0; i < params1.Length; i++)
+                    {
+                        if (!params1[i].ParameterType.IsAssignableFrom(params2[i].ParameterType))
+                        {
+                            return false;
+                        }
+                    }
+
+                    return true;
+                }
+            }
         }
 
         [RequiresUnreferencedCode(Queryable.InMemoryQueryableExtensionMethodsRequiresUnreferencedCode)]

src/libraries/System.Linq.Queryable/tests/FirstOrDefaultTests.cs

@@ -129,5 +129,16 @@ public void FirstOrDefault2()
             var val = (new int[] { 0, 1, 2 }).AsQueryable().FirstOrDefault(n => n > 1);
             Assert.Equal(2, val);
         }
+
+        [Fact]
+        public void FirstOrDefault_OverloadResolution_Regression()
+        {
+            // Regression test for https://github.com/dotnet/runtime/issues/65419
+            object? result = new object[] { 1, "" }.AsQueryable().FirstOrDefault(x => x is string);
+            Assert.IsType<string>(result);
+
+            result = Array.Empty<object>().AsQueryable().FirstOrDefault(1);
+            Assert.IsType<int>(result);
+        }
     }
 }

src/libraries/System.Linq.Queryable/tests/LastOrDefaultTests.cs

@@ -96,5 +96,16 @@ public void LastOrDefault2()
             var val = (new int[] { 0, 1, 2 }).AsQueryable().LastOrDefault(n => n > 1);
             Assert.Equal(2, val);
         }
+
+        [Fact]
+        public void LastOrDefault_OverloadResolution_Regression()
+        {
+            // Regression test for https://github.com/dotnet/runtime/issues/65419
+            object? result = new object[] { 1, "" }.AsQueryable().LastOrDefault(x => x is int);
+            Assert.IsType<int>(result);
+
+            result = Array.Empty<object>().AsQueryable().LastOrDefault(1);
+            Assert.IsType<int>(result);
+        }
     }
 }

src/libraries/System.Linq.Queryable/tests/SingleOrDefaultTests.cs

@@ -79,5 +79,16 @@ public void SingleOrDefault2()
             var val = (new int[] { 2 }).AsQueryable().SingleOrDefault(n => n > 1);
             Assert.Equal(2, val);
         }
+
+        [Fact]
+        public void SingleOrDefault_OverloadResolution_Regression()
+        {
+            // Regression test for https://github.com/dotnet/runtime/issues/65419
+            object? result = new object[] { 1, "" }.AsQueryable().SingleOrDefault(x => x is string);
+            Assert.IsType<string>(result);
+
+            result = Array.Empty<object>().AsQueryable().SingleOrDefault(1);
+            Assert.IsType<int>(result);
+        }
     }
 }