fix: enum parsing when encountering unknown values should not default to first member

src/Microsoft.OpenApi/Extensions/StringExtensions.cs

@@ -2,47 +2,61 @@
 // Licensed under the MIT license.
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using Microsoft.OpenApi.Attributes;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Reader;
 
 namespace Microsoft.OpenApi.Extensions
 {
     /// <summary>
     /// String extension methods.
     /// </summary>
-    public static class StringExtensions
+    internal static class StringExtensions
     {
-        private static readonly ConcurrentDictionary<Type, ConcurrentDictionary<string, object>> EnumDisplayCache = new();
+        private static readonly ConcurrentDictionary<Type, ReadOnlyDictionary<string, object>> EnumDisplayCache = new();
 
-        /// <summary>
-        /// Gets the enum value based on the given enum type and display name.
-        /// </summary>
-        /// <param name="displayName">The display name.</param>
-        public static T GetEnumFromDisplayName<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields)] T>(this string displayName)
+        internal static bool TryGetEnumFromDisplayName<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields)] T>(this string displayName, ParsingContext parsingContext, out T result) where T : Enum
+        {
+            if (TryGetEnumFromDisplayName(displayName, out result))
+            {
+                return true;
+            }
+
+            parsingContext.Diagnostic.Errors.Add(new OpenApiError(parsingContext.GetLocation(), $"Enum value {displayName} is not recognized."));
+            return false;
+
+        }
+        internal static bool TryGetEnumFromDisplayName<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicFields)] T>(this string displayName, out T result) where T : Enum
         {
             var type = typeof(T);
-            if (!type.IsEnum)
-                return default;
 
-            var displayMap = EnumDisplayCache.GetOrAdd(type, _ => new ConcurrentDictionary<string, object>(StringComparer.OrdinalIgnoreCase));
+            var displayMap = EnumDisplayCache.GetOrAdd(type, GetEnumValues<T>);
 
             if (displayMap.TryGetValue(displayName, out var cachedValue))
-                return (T)cachedValue;
-
+            {
+                result = (T)cachedValue;
+                return true;
+            }
 
-            foreach (var field in type.GetFields(BindingFlags.Public | BindingFlags.Static))
+            result = default;
+            return false;
+        }
+        private static ReadOnlyDictionary<string, object> GetEnumValues<T>(Type enumType) where T : Enum
+        {
+            var result = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
+            foreach (var field in enumType.GetFields(BindingFlags.Public | BindingFlags.Static))
             {
-                var displayAttribute = field.GetCustomAttribute<DisplayAttribute>();
-                if (displayAttribute != null && displayAttribute.Name.Equals(displayName, StringComparison.OrdinalIgnoreCase))
+                if (field.GetCustomAttribute<DisplayAttribute>() is {} displayAttribute)
                 {
                     var enumValue = (T)field.GetValue(null);
-                    displayMap.TryAdd(displayName, enumValue);
-                    return enumValue;
+                    result.Add(displayAttribute.Name, enumValue);
                 }
             }
-
-            return default;
+            return new ReadOnlyDictionary<string, object>(result);
         }
         internal static string ToFirstCharacterLowerCase(this string input)
             => string.IsNullOrEmpty(input) ? string.Empty : char.ToLowerInvariant(input[0]) + input.Substring(1);

src/Microsoft.OpenApi/Models/OpenApiSecurityScheme.cs

@@ -17,7 +17,7 @@
         /// <summary>
         /// REQUIRED. The type of the security scheme. Valid values are "apiKey", "http", "oauth2", "openIdConnect".
         /// </summary>
-        public virtual SecuritySchemeType Type { get; set; }
+        public virtual SecuritySchemeType? Type { get; set; }
 
         /// <summary>
         /// A short description for security scheme. CommonMark syntax MAY be used for rich text representation.
@@ -32,7 +32,7 @@
         /// <summary>
         /// REQUIRED. The location of the API key. Valid values are "query", "header" or "cookie".
         /// </summary>
-        public virtual ParameterLocation In { get; set; }
+        public virtual ParameterLocation? In { get; set; }
 
         /// <summary>
         /// REQUIRED. The name of the HTTP Authorization scheme to be used
@@ -82,10 +82,10 @@
         /// </summary>
         public OpenApiSecurityScheme(OpenApiSecurityScheme securityScheme)
         {
-            Type = securityScheme?.Type ?? Type;
+            Type = securityScheme?.Type;
             Description = securityScheme?.Description ?? Description;
             Name = securityScheme?.Name ?? Name;
-            In = securityScheme?.In ?? In;
+            In = securityScheme?.In;
             Scheme = securityScheme?.Scheme ?? Scheme;
             BearerFormat = securityScheme?.BearerFormat ?? BearerFormat;
             Flows = securityScheme?.Flows != null ? new(securityScheme?.Flows) : null;
@@ -111,7 +111,7 @@
             SerializeInternal(writer, OpenApiSpecVersion.OpenApi3_0, (writer, element) => element.SerializeAsV3(writer));
         }
 
-        internal virtual void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version, 
+        internal virtual void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion version,
             Action<IOpenApiWriter, IOpenApiSerializable> callback)
         {
             Utils.CheckArgumentNull(writer);

src/Microsoft.OpenApi/Models/References/OpenApiSecuritySchemeReference.cs

@@ -71,7 +71,7 @@ public override string Description
         public override string Name { get => Target.Name; set => Target.Name = value; }
 
         /// <inheritdoc/>
-        public override ParameterLocation In { get => Target.In; set => Target.In = value; }
+        public override ParameterLocation? In { get => Target.In; set => Target.In = value; }
 
         /// <inheritdoc/>
         public override string Scheme { get => Target.Scheme; set => Target.Scheme = value; }
@@ -89,7 +89,7 @@ public override string Description
         public override IDictionary<string, IOpenApiExtension> Extensions { get => Target.Extensions; set => Target.Extensions = value; }
 
         /// <inheritdoc/>
-        public override SecuritySchemeType Type { get => Target.Type; set => Target.Type = value; }
+        public override SecuritySchemeType? Type { get => Target.Type; set => Target.Type = value; }
 
         /// <inheritdoc/>
         public override void SerializeAsV3(IOpenApiWriter writer)

src/Microsoft.OpenApi/Reader/V2/OpenApiParameterDeserializer.cs

@@ -172,7 +172,8 @@ private static void ProcessIn(OpenApiParameter o, ParseNode n, OpenApiDocument h
                 case "query":
                 case "header":
                 case "path":
-                    o.In = value.GetEnumFromDisplayName<ParameterLocation>();
+                    value.TryGetEnumFromDisplayName<ParameterLocation>(out var _in);
+                    o.In = _in;
                     break;
                 default:
                     o.In = null;

src/Microsoft.OpenApi/Reader/V2/OpenApiSecuritySchemeDeserializer.cs

@@ -40,12 +40,24 @@
                             case "oauth2":
                                 o.Type = SecuritySchemeType.OAuth2;
                                 break;
+
+                            default:
+                                n.Context.Diagnostic.Errors.Add(new OpenApiError(n.Context.GetLocation(), $"Security scheme type {type} is not recognized."));
+                                break;
                         }
                     }
                 },
                 {"description", (o, n, _) => o.Description = n.GetScalarValue()},
                 {"name", (o, n, _) => o.Name = n.GetScalarValue()},
-                {"in", (o, n, _) => o.In = n.GetScalarValue().GetEnumFromDisplayName<ParameterLocation>()},
+                {"in", (o, n, _) => 
+                    {
+                        if (!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterLocation>(n.Context, out var _in))
+                        {
+                            return;
+                        }
+                        o.In = _in;
+                    }
+                },
                 {
                     "flow", (_, n, _) => _flowValue = n.GetScalarValue()
                 },
@@ -71,7 +83,7 @@
         public static OpenApiSecurityScheme LoadSecurityScheme(ParseNode node, OpenApiDocument hostDocument = null)
         {
             // Reset the local variables every time this method is called.
             // TODO: Change _flow to a tempStorage variable to make the deserializer thread-safe.
             _flowValue = null;
             _flow = new();
 

src/Microsoft.OpenApi/Reader/V3/OpenApiEncodingDeserializer.cs

@@ -25,7 +25,14 @@ internal static partial class OpenApiV3Deserializer
             },
             {
                 "style",
-                (o, n, _) => o.Style = n.GetScalarValue().GetEnumFromDisplayName<ParameterStyle>()
+                (o, n, _) => 
+                {
+                    if(!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterStyle>(n.Context, out var style))
+                    {
+                        return;
+                    }
+                    o.Style = style;
+                }
             },
             {
                 "explode",

src/Microsoft.OpenApi/Reader/V3/OpenApiHeaderDeserializer.cs

@@ -39,7 +39,14 @@ internal static partial class OpenApiV3Deserializer
             },
             {
                 "style",
-                (o, n, _) => o.Style = n.GetScalarValue().GetEnumFromDisplayName<ParameterStyle>()
+                (o, n, _) => 
+                {
+                    if(!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterStyle>(n.Context, out var style))
+                    {
+                        return;
+                    }
+                    o.Style = style;
+                }
             },
             {
                 "explode",

src/Microsoft.OpenApi/Reader/V3/OpenApiParameterDeserializer.cs

@@ -26,11 +26,11 @@ internal static partial class OpenApiV3Deserializer
                 {
                     "in", (o, n, _) =>
                     {
-                        var inString = n.GetScalarValue();
-
-                        o.In = Enum.GetValues(typeof(ParameterLocation)).Cast<ParameterLocation>()
-                            .Select( e => e.GetDisplayName() )
-                            .Contains(inString) ? n.GetScalarValue().GetEnumFromDisplayName<ParameterLocation>() : null;
+                        if (!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterLocation>(n.Context, out var _in))
+                        {
+                            return;
+                        }
+                        o.In = _in;
                     }
                 },
                 {
@@ -55,7 +55,14 @@ internal static partial class OpenApiV3Deserializer
                 },
                 {
                     "style",
-                    (o, n, _) => o.Style = n.GetScalarValue().GetEnumFromDisplayName<ParameterStyle>()
+                    (o, n, _) => 
+                    {
+                        if (!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterStyle>(n.Context, out var style))
+                        {
+                            return;
+                        }
+                        o.Style = style;
+                    }
                 },
                 {
                     "explode",

src/Microsoft.OpenApi/Reader/V3/OpenApiSecuritySchemeDeserializer.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license.
 
 using System;
-using System.Linq;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Models.References;
@@ -21,7 +20,14 @@ internal static partial class OpenApiV3Deserializer
             {
                 {
                     "type",
-                    (o, n, _) => o.Type = n.GetScalarValue().GetEnumFromDisplayName<SecuritySchemeType>()
+                    (o, n, _) => 
+                    {
+                        if (!n.GetScalarValue().TryGetEnumFromDisplayName<SecuritySchemeType>(n.Context, out var type))
+                        {
+                            return;
+                        }
+                        o.Type = type;
+                    }
                 },
                 {
                     "description",
@@ -33,7 +39,14 @@ internal static partial class OpenApiV3Deserializer
                 },
                 {
                     "in",
-                    (o, n, _) => o.In = n.GetScalarValue().GetEnumFromDisplayName<ParameterLocation>()
+                    (o, n, _) => 
+                    {
+                        if(!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterLocation>(n.Context, out var _in))
+                        {
+                            return;
+                        }
+                        o.In = _in;
+                    }
                 },
                 {
                     "scheme",

src/Microsoft.OpenApi/Reader/V3/OpenApiV3VersionService.cs

@@ -123,7 +123,7 @@ public OpenApiReference ConvertToOpenApiReference(
                     if (id.StartsWith("/components/"))
                     {
                         var localSegments = segments[1].Split('/');
-                        var referencedType = localSegments[2].GetEnumFromDisplayName<ReferenceType>();
+                        localSegments[2].TryGetEnumFromDisplayName<ReferenceType>(out var referencedType);
                         if (type == null)
                         {
                             type = referencedType;
@@ -200,25 +200,22 @@ private OpenApiReference ParseLocalReference(string localReference)
 
             var segments = localReference.Split('/');
 
-            if (segments.Length == 4) // /components/{type}/pet
+            if (segments.Length == 4 && segments[1] == "components") // /components/{type}/pet
             {
-                if (segments[1] == "components")
+                segments[2].TryGetEnumFromDisplayName<ReferenceType>(out var referenceType);
+                var refId = segments[3];
+                if (segments[2] == "pathItems")
                 {
-                    var referenceType = segments[2].GetEnumFromDisplayName<ReferenceType>();
-                    var refId = segments[3];
-                    if (segments[2] == "pathItems")
-                    {
-                        refId = "/" + segments[3];
-                    };
+                    refId = "/" + segments[3];
+                }
 
-                    var parsedReference = new OpenApiReference
-                    {
-                        Type = referenceType,
-                        Id = refId
-                    };
+                var parsedReference = new OpenApiReference
+                {
+                    Type = referenceType,
+                    Id = refId
+                };
 
-                    return parsedReference;
-                }
+                return parsedReference;
             }
 
             throw new OpenApiException(string.Format(SRResource.ReferenceHasInvalidFormat, localReference));

src/Microsoft.OpenApi/Reader/V31/OpenApiEncodingDeserializer.cs

@@ -27,7 +27,11 @@ internal static partial class OpenApiV31Deserializer
             {
                 "style", (o, n, _) =>
                 {
-                    o.Style = n.GetScalarValue().GetEnumFromDisplayName<ParameterStyle>();
+                    if(!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterStyle>(n.Context, out var style))
+                    {
+                        return;
+                    }
+                    o.Style = style;
                 }
             },
             {

src/Microsoft.OpenApi/Reader/V31/OpenApiHeaderDeserializer.cs

@@ -47,7 +47,11 @@ internal static partial class OpenApiV31Deserializer
             {
                 "style", (o, n, _) =>
                 {
-                    o.Style = n.GetScalarValue().GetEnumFromDisplayName<ParameterStyle>();
+                    if(!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterStyle>(n.Context, out var style))
+                    {
+                        return;
+                    }
+                    o.Style = style;
                 }
             },
             {

src/Microsoft.OpenApi/Reader/V31/OpenApiParameterDeserializer.cs

@@ -25,11 +25,11 @@ internal static partial class OpenApiV31Deserializer
                 {
                     "in", (o, n, _) =>
                     {
-                        var inString = n.GetScalarValue();
-                        o.In = Enum.GetValues(typeof(ParameterLocation)).Cast<ParameterLocation>()
-                            .Select( e => e.GetDisplayName() )
-                            .Contains(inString) ? n.GetScalarValue().GetEnumFromDisplayName<ParameterLocation>() : null;
-
+                        if (!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterLocation>(n.Context, out var _in))
+                        {
+                            return;
+                        }
+                        o.In = _in;
                     }
                 },
                 {
@@ -65,7 +65,11 @@ internal static partial class OpenApiV31Deserializer
                 {
                     "style", (o, n, _) =>
                     {
-                        o.Style = n.GetScalarValue().GetEnumFromDisplayName<ParameterStyle>();
+                        if (!n.GetScalarValue().TryGetEnumFromDisplayName<ParameterStyle>(n.Context, out var style))
+                        {
+                            return;
+                        }
+                        o.Style = style;
                     }
                 },
                 {