Fix NullReferenceException in SqlServerStringMethodTranslator.TranslateIndexOf for casted parameters (#37956)

Fixes #37940

Author: Copilot

src/EFCore.SqlServer/Query/Internal/Translators/SqlServerStringMethodTranslator.cs

@@ -220,7 +220,8 @@ private SqlExpression TranslateIndexOf(
         SqlExpression searchExpression,
         SqlExpression? startIndex)
     {
-        var stringTypeMapping = ExpressionExtensions.InferTypeMapping(instance, searchExpression)!;
+        var stringTypeMapping = ExpressionExtensions.InferTypeMapping(instance, searchExpression)
+            ?? sqlExpressionFactory.ApplyDefaultTypeMapping(instance)!.TypeMapping!;
         searchExpression = sqlExpressionFactory.ApplyTypeMapping(
             searchExpression, searchExpression.Type == typeof(char) ? CharTypeMapping.Default : stringTypeMapping);
 

test/EFCore.Relational.Specification.Tests/Query/Translations/StringTranslationsRelationalTestBase.cs

@@ -72,4 +72,27 @@ public virtual Task Like_with_non_string_column_using_double_cast()
             ss => ss.Set<BasicTypesEntity>().Where(o => o.Int.ToString().Contains("5")));
 
     #endregion Like
+
+    #region IndexOf
+
+    [ConditionalFact]
+    public virtual Task IndexOf_with_non_string_column_using_double_cast()
+    {
+        var pattern = "5";
+        return AssertQuery(
+            ss => ss.Set<BasicTypesEntity>().Where(b => ((string)(object)b.Int).IndexOf(pattern) != -1),
+            ss => ss.Set<BasicTypesEntity>().Where(b => b.Int.ToString().Contains(pattern)));
+    }
+
+    #endregion IndexOf
+
+    #region Replace
+
+    [ConditionalFact]
+    public virtual Task Replace_with_non_string_column_using_double_cast()
+        => AssertQuery(
+            ss => ss.Set<BasicTypesEntity>().Where(b => ((string)(object)b.Int).Replace("8", "3") == "3"),
+            ss => ss.Set<BasicTypesEntity>().Where(b => b.Int.ToString().Replace("8", "3") == "3"));
+
+    #endregion Replace
 }

test/EFCore.SqlServer.FunctionalTests/Query/Translations/StringTranslationsSqlServerTest.cs

@@ -273,6 +273,23 @@ ELSE 1
 """);
     }
 
+    public override async Task IndexOf_with_non_string_column_using_double_cast()
+    {
+        await base.IndexOf_with_non_string_column_using_double_cast();
+
+        AssertSql(
+            """
+@pattern='5' (Size = 4000)
+
+SELECT [b].[Id], [b].[Bool], [b].[Byte], [b].[ByteArray], [b].[DateOnly], [b].[DateTime], [b].[DateTimeOffset], [b].[Decimal], [b].[Double], [b].[Enum], [b].[FlagsEnum], [b].[Float], [b].[Guid], [b].[Int], [b].[Long], [b].[Short], [b].[String], [b].[TimeOnly], [b].[TimeSpan]
+FROM [BasicTypesEntities] AS [b]
+WHERE CAST(CHARINDEX(@pattern, CAST([b].[Int] AS nvarchar(max))) AS int) - CASE
+    WHEN @pattern = N'' THEN 0
+    ELSE 1
+END <> -1
+""");
+    }
+
     #endregion IndexOf
 
     #region Replace
@@ -325,6 +342,18 @@ FROM [BasicTypesEntities] AS [b]
 """);
     }
 
+    public override async Task Replace_with_non_string_column_using_double_cast()
+    {
+        await base.Replace_with_non_string_column_using_double_cast();
+
+        AssertSql(
+            """
+SELECT [b].[Id], [b].[Bool], [b].[Byte], [b].[ByteArray], [b].[DateOnly], [b].[DateTime], [b].[DateTimeOffset], [b].[Decimal], [b].[Double], [b].[Enum], [b].[FlagsEnum], [b].[Float], [b].[Guid], [b].[Int], [b].[Long], [b].[Short], [b].[String], [b].[TimeOnly], [b].[TimeSpan]
+FROM [BasicTypesEntities] AS [b]
+WHERE REPLACE(CAST([b].[Int] AS nvarchar(max)), N'8', N'3') = N'3'
+""");
+    }
+
     #endregion Replace
 
     #region Substring

test/EFCore.Sqlite.FunctionalTests/Query/Translations/StringTranslationsSqliteTest.cs

@@ -263,6 +263,20 @@ WHERE instr('12559', CAST("b"."Int" AS TEXT)) - 1 = 1
 """);
     }
 
+    public override async Task IndexOf_with_non_string_column_using_double_cast()
+    {
+        await base.IndexOf_with_non_string_column_using_double_cast();
+
+        AssertSql(
+            """
+@pattern='5' (Size = 1)
+
+SELECT "b"."Id", "b"."Bool", "b"."Byte", "b"."ByteArray", "b"."DateOnly", "b"."DateTime", "b"."DateTimeOffset", "b"."Decimal", "b"."Double", "b"."Enum", "b"."FlagsEnum", "b"."Float", "b"."Guid", "b"."Int", "b"."Long", "b"."Short", "b"."String", "b"."TimeOnly", "b"."TimeSpan"
+FROM "BasicTypesEntities" AS "b"
+WHERE instr(CAST("b"."Int" AS TEXT), @pattern) - 1 <> -1
+""");
+    }
+
     #endregion IndexOf
 
     #region Replace
@@ -315,6 +329,18 @@ public override async Task Replace_using_property_arguments()
 """);
     }
 
+    public override async Task Replace_with_non_string_column_using_double_cast()
+    {
+        await base.Replace_with_non_string_column_using_double_cast();
+
+        AssertSql(
+            """
+SELECT "b"."Id", "b"."Bool", "b"."Byte", "b"."ByteArray", "b"."DateOnly", "b"."DateTime", "b"."DateTimeOffset", "b"."Decimal", "b"."Double", "b"."Enum", "b"."FlagsEnum", "b"."Float", "b"."Guid", "b"."Int", "b"."Long", "b"."Short", "b"."String", "b"."TimeOnly", "b"."TimeSpan"
+FROM "BasicTypesEntities" AS "b"
+WHERE replace(CAST("b"."Int" AS TEXT), '8', '3') = '3'
+""");
+    }
+
     #endregion Replace
 
     #region Substring