CSHARP-5563: Code review changes.

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpressionExtensions.cs

@@ -20,100 +20,88 @@ namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions
     internal static class AstExpressionExtensions
     {
         public static bool IsBooleanConstant(this AstExpression expression)
-            =>
-                expression is AstConstantExpression constantExpression &&
-                constantExpression.Value.IsBoolean;
+            => expression.IsConstant<BsonBoolean>(out _);
 
-        public static bool IsBooleanConstant(this AstExpression expression, out bool value)
+        public static bool IsBooleanConstant(this AstExpression expression, out bool booleanConstant)
         {
-            if (expression is AstConstantExpression constantExpression && constantExpression.Value is BsonBoolean bsonBoolean)
+            if (expression.IsConstant<BsonBoolean>(out var bsonBooleanConstant))
             {
-                value = bsonBoolean.Value;
+                booleanConstant = bsonBooleanConstant.Value;
                 return true;
             }
 
-            value = default;
+            booleanConstant = default;
             return false;
         }
 
         public static bool IsBsonNull(this AstExpression expression)
-            =>
-                expression is AstConstantExpression constantExpression &&
-                constantExpression.Value.IsBsonNull;
+            => expression.IsConstant(out var constant) && constant.IsBsonNull;
 
-        public static bool IsConstant(this AstExpression expression, out BsonValue value)
+        public static bool IsConstant(this AstExpression expression, out BsonValue constant)
         {
             if (expression is AstConstantExpression constantExpression)
             {
-                value = constantExpression.Value;
+                constant = constantExpression.Value;
                 return true;
             }
 
-            value = null;
+            constant = null;
             return false;
         }
 
-        public static bool IsConstant<TBsonValue>(this AstExpression expression, out TBsonValue value)
+        public static bool IsConstant<TBsonValue>(this AstExpression expression, out TBsonValue constant)
             where TBsonValue : BsonValue
         {
-            if (expression is AstConstantExpression constantExpression && constantExpression.Value is TBsonValue bsonValue)
+            if (expression.IsConstant(out var bsonValueConstant) && bsonValueConstant is TBsonValue derivedBsonValueConstant)
             {
-                value = bsonValue;
+                constant = derivedBsonValueConstant;
                 return true;
             }
 
-            value = null;
+            constant = null;
             return false;
         }
 
         public static bool IsInt32Constant(this AstExpression expression)
-            =>
-                expression is AstConstantExpression constantExpression &&
-                constantExpression.Value.IsInt32;
+            => expression.IsConstant<BsonInt32>(out _);
 
-        public static bool IsInt32Constant(this AstExpression expression, int value)
-            =>
-                expression is AstConstantExpression constantExpression &&
-                constantExpression.Value is BsonInt32 bsonInt32 &&
-                bsonInt32.Value == value;
+        public static bool IsInt32Constant(this AstExpression expression, int comparand)
+            => expression.IsInt32Constant(out var int32Constant) && int32Constant == comparand;
 
-        public static bool IsInt32Constant(this AstExpression expression, out int value)
+        public static bool IsInt32Constant(this AstExpression expression, out int int32Constant)
         {
-            if (expression is AstConstantExpression constantExpression && constantExpression.Value is BsonInt32 bsonInt32)
+            if (expression.IsConstant<BsonInt32>(out var bsonInt32Constant))
             {
-                value = bsonInt32.Value;
+                int32Constant = bsonInt32Constant.Value;
                 return true;
             }
 
-            value = default;
+            int32Constant = default;
             return false;
         }
 
         public static bool IsMaxInt32(this AstExpression expression)
-            => expression.IsInt32Constant(out var value) && value == int.MaxValue;
+            => expression.IsInt32Constant(out var int32Constant) && int32Constant == int.MaxValue;
 
         public static bool IsRootVar(this AstExpression expression)
             => expression is AstVarExpression varExpression && varExpression.Name == "ROOT" && varExpression.IsCurrent;
 
-        public static bool IsStringConstant(this AstExpression expression, string value)
-            =>
-                expression is AstConstantExpression constantExpression &&
-                constantExpression.Value is BsonString bsonString &&
-                bsonString.Value == value;
+        public static bool IsStringConstant(this AstExpression expression, string comparand)
+            => expression.IsStringConstant(out var stringConstant) && stringConstant == comparand;
 
-        public static bool IsStringConstant(this AstExpression expression, out string value)
+        public static bool IsStringConstant(this AstExpression expression, out string stringConstant)
         {
-            if (expression is AstConstantExpression constantExpression && constantExpression.Value is BsonString bsonString)
+            if (expression.IsConstant<BsonString>(out var bsonStringConstant))
             {
-                value = bsonString.Value;
+                stringConstant = bsonStringConstant.Value;
                 return true;
             }
 
-            value = default;
+            stringConstant = default;
             return false;
         }
 
        public static bool IsZero(this AstExpression expression)
-            => expression is AstConstantExpression constantExpression && constantExpression.Value == 0;
+            => expression.IsConstant(out var constant) && constant == 0; // works for all numeric BSON types
     }
 }

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Optimizers/AstSimplifier.cs

@@ -51,7 +51,7 @@ public override AstNode VisitBinaryExpression(AstBinaryExpression node)
                 {
                     // { $ifNull : [expr1, expr2] } => expr2 when expr1 == null
                     // { $ifNull : [expr1, expr2] } => expr1 when expr1 != null
-                    return arg1Constant == BsonNull.Value ? arg2 : arg1;
+                    return arg1Constant.IsBsonNull ? arg2 : arg1;
                 }
 
                 if (arg2.IsBsonNull())