C#: Avoid string concatenation when looking up enum values by name.

PiperOrigin-RevId: 616745400

csharp/src/Google.Protobuf/Reflection/DescriptorPool.cs

@@ -27,6 +27,9 @@ internal sealed class DescriptorPool
         private readonly IDictionary<ObjectIntPair<IDescriptor>, EnumValueDescriptor> enumValuesByNumber =
             new Dictionary<ObjectIntPair<IDescriptor>, EnumValueDescriptor>();
 
+        private readonly IDictionary<EnumValueByNameDescriptorKey, EnumValueDescriptor> enumValuesByName =
+            new Dictionary<EnumValueByNameDescriptorKey, EnumValueDescriptor>();
+
         private readonly HashSet<FileDescriptor> dependencies = new HashSet<FileDescriptor>();
 
         internal DescriptorPool(IEnumerable<FileDescriptor> dependencyFiles)
@@ -129,29 +132,20 @@ internal void AddSymbol(IDescriptor descriptor)
 
             if (descriptorsByName.TryGetValue(fullName, out IDescriptor old))
             {
-                int dotPos = fullName.LastIndexOf('.');
-                string message;
-                if (descriptor.File == old.File)
-                {
-                    if (dotPos == -1)
-                    {
-                        message = "\"" + fullName + "\" is already defined.";
-                    }
-                    else
-                    {
-                        message = "\"" + fullName.Substring(dotPos + 1) + "\" is already defined in \"" +
-                                  fullName.Substring(0, dotPos) + "\".";
-                    }
-                }
-                else
-                {
-                    message = "\"" + fullName + "\" is already defined in file \"" + old.File.Name + "\".";
-                }
-                throw new DescriptorValidationException(descriptor, message);
+                throw new DescriptorValidationException(descriptor,
+                    GetDescriptorAlreadyAddedExceptionMessage(descriptor, fullName, old));
             }
             descriptorsByName[fullName] = descriptor;
         }
 
+        private static string GetDescriptorAlreadyAddedExceptionMessage(IDescriptor descriptor, string fullName, IDescriptor old)
+        {
+            int dotPos = fullName.LastIndexOf('.');
+            return descriptor.File != old.File ? $"\"{fullName}\" is already defined in file \"{old.File.Name}\"."
+                : dotPos == -1 ? $"{fullName} is already defined."
+                : $"\"{fullName.Substring(dotPos + 1)}\" is already defined in \"{fullName.Substring(0, dotPos)}\".";
+        }
+
         /// <summary>
         /// Verifies that the descriptor's name is valid (i.e. it contains
         /// only letters, digits and underscores, and does not start with a digit).
@@ -167,11 +161,14 @@ private static void ValidateSymbolName(IDescriptor descriptor)
             // Symbol name must start with a letter or underscore, and it can contain letters,
             // numbers and underscores.
             string name = descriptor.Name;
-            if (!IsAsciiLetter(name[0]) && name[0] != '_') {
+            if (!IsAsciiLetter(name[0]) && name[0] != '_')
+            {
                 ThrowInvalidSymbolNameException(descriptor);
             }
-            for (int i = 1; i < name.Length; i++) {
-                if (!IsAsciiLetter(name[i]) && !IsAsciiDigit(name[i]) && name[i] != '_') {
+            for (int i = 1; i < name.Length; i++)
+            {
+                if (!IsAsciiLetter(name[i]) && !IsAsciiDigit(name[i]) && name[i] != '_')
+                {
                     ThrowInvalidSymbolNameException(descriptor);
                 }
             }
@@ -199,6 +196,12 @@ internal EnumValueDescriptor FindEnumValueByNumber(EnumDescriptor enumDescriptor
             return ret;
         }
 
+        internal EnumValueDescriptor FindEnumValueByName(EnumDescriptor enumDescriptor, string name)
+        {
+            enumValuesByName.TryGetValue(new EnumValueByNameDescriptorKey(enumDescriptor, name), out EnumValueDescriptor ret);
+            return ret;
+        }
+
         /// <summary>
         /// Adds a field to the fieldsByNumber table.
         /// </summary>
@@ -219,17 +222,28 @@ internal void AddFieldByNumber(FieldDescriptor field)
         }
 
         /// <summary>
-        /// Adds an enum value to the enumValuesByNumber table. If an enum value
-        /// with the same type and number already exists, this method does nothing.
-        /// (This is allowed; the first value defined with the number takes precedence.)
+        /// Adds an enum value to the enumValuesByNumber and enumValuesByName tables. If an enum value
+        /// with the same type and number already exists, this method does nothing to enumValuesByNumber.
+        /// (This is allowed; the first value defined with the number takes precedence.) If an enum
+        /// value with the same name already exists, this method throws DescriptorValidationException.
+        /// (It is expected that this method is called after AddSymbol, which would already have thrown
+        /// an exception in this failure case.)
         /// </summary>
-        internal void AddEnumValueByNumber(EnumValueDescriptor enumValue)
+        internal void AddEnumValue(EnumValueDescriptor enumValue)
         {
-            ObjectIntPair<IDescriptor> key = new ObjectIntPair<IDescriptor>(enumValue.EnumDescriptor, enumValue.Number);
-            if (!enumValuesByNumber.ContainsKey(key))
+            ObjectIntPair<IDescriptor> numberKey = new ObjectIntPair<IDescriptor>(enumValue.EnumDescriptor, enumValue.Number);
+            if (!enumValuesByNumber.ContainsKey(numberKey))
             {
-                enumValuesByNumber[key] = enumValue;
+                enumValuesByNumber[numberKey] = enumValue;
             }
+
+            EnumValueByNameDescriptorKey nameKey = new EnumValueByNameDescriptorKey(enumValue.EnumDescriptor, enumValue.Name);
+            if (enumValuesByName.TryGetValue(nameKey, out EnumValueDescriptor old))
+            {
+                throw new DescriptorValidationException(enumValue,
+                GetDescriptorAlreadyAddedExceptionMessage(enumValue, enumValue.FullName, old));
+            }
+            enumValuesByName[nameKey] = enumValue;
         }
 
         /// <summary>
@@ -308,5 +322,37 @@ internal IDescriptor LookupSymbol(string name, IDescriptor relativeTo)
                 return result;
             }
         }
-    }
+
+        /// <summary>
+        /// Struct used to hold the keys for the enumValuesByName table.
+        /// </summary>
+        private struct EnumValueByNameDescriptorKey : IEquatable<EnumValueByNameDescriptorKey>
+        {
+            private readonly string name;
+            private readonly IDescriptor descriptor;
+
+            internal EnumValueByNameDescriptorKey(EnumDescriptor descriptor, string valueName)
+            {
+                this.descriptor = descriptor;
+                this.name = valueName;
+            }
+
+            public bool Equals(EnumValueByNameDescriptorKey other) =>
+                descriptor == other.descriptor
+                && name == other.name;
+
+            public override bool Equals(object obj) =>
+                obj is EnumValueByNameDescriptorKey pair && Equals(pair);
+
+            public override int GetHashCode()
+            {
+                unchecked
+                {
+                    var hashCode = descriptor.GetHashCode();
+                    hashCode = (hashCode * 397) ^ (name != null ? name.GetHashCode() : 0);
+                    return hashCode;
+                }
+            }
+        }
+   }
 }

csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs

@@ -90,10 +90,8 @@ public EnumValueDescriptor FindValueByNumber(int number)
         /// </summary>
         /// <param name="name">The unqualified name of the value (e.g. "FOO").</param>
         /// <returns>The value's descriptor, or null if not found.</returns>
-        public EnumValueDescriptor FindValueByName(string name)
-        {
-            return File.DescriptorPool.FindSymbol<EnumValueDescriptor>(FullName + "." + name);
-        }
+        public EnumValueDescriptor FindValueByName(string name) =>
+            File.DescriptorPool.FindEnumValueByName(this, name);
 
         /// <summary>
         /// The (possibly empty) set of custom options for this enum.

csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs

@@ -24,7 +24,7 @@ public sealed class EnumValueDescriptor : DescriptorBase
             Proto = proto;
             EnumDescriptor = parent;
             file.DescriptorPool.AddSymbol(this);
-            file.DescriptorPool.AddEnumValueByNumber(this);
+            file.DescriptorPool.AddEnumValue(this);
         }
 
         internal EnumValueDescriptorProto Proto { get; }