fix/unique tags

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -76,10 +76,27 @@
         public IList<OpenApiSecurityRequirement>? SecurityRequirements { get; set; } =
             new List<OpenApiSecurityRequirement>();
 
+        private HashSet<OpenApiTag>? _tags;
         /// <summary>
         /// A list of tags used by the specification with additional metadata.
         /// </summary>
-        public IList<OpenApiTag>? Tags { get; set; } = new List<OpenApiTag>();
+        public ISet<OpenApiTag>? Tags 
+        { 
+            get
+            {
+                return _tags;
+            }
+            set
+            {
+                if (value is null)
+                {
+                    return;
+                }
+                _tags = value is HashSet<OpenApiTag> tags && tags.Comparer is OpenApiTagComparer ?
+                        tags :
+                        new HashSet<OpenApiTag>(value, OpenApiTagComparer.Instance);
+            }
+        }
 
         /// <summary>
         /// Additional external documentation.
@@ -123,7 +140,7 @@
             Webhooks = document?.Webhooks != null ? new Dictionary<string, IOpenApiPathItem>(document.Webhooks) : null;
             Components = document?.Components != null ? new(document?.Components) : null;
             SecurityRequirements = document?.SecurityRequirements != null ? new List<OpenApiSecurityRequirement>(document.SecurityRequirements) : null;
-            Tags = document?.Tags != null ? new List<OpenApiTag>(document.Tags) : null;
+            Tags = document?.Tags != null ? new HashSet<OpenApiTag>(document.Tags, OpenApiTagComparer.Instance) : null;
             ExternalDocs = document?.ExternalDocs != null ? new(document?.ExternalDocs) : null;
             Extensions = document?.Extensions != null ? new Dictionary<string, IOpenApiExtension>(document.Extensions) : null;
             Annotations = document?.Annotations != null ? new Dictionary<string, object>(document.Annotations) : null;
@@ -222,7 +239,7 @@
         /// <summary>
         /// Serialize <see cref="OpenApiDocument"/> to OpenAPI object V2.0.
         /// </summary>
         public void SerializeAsV2(IOpenApiWriter writer)
         {
             Utils.CheckArgumentNull(writer);
 
@@ -516,7 +533,7 @@
             }
             else
             {
                 string relativePath = OpenApiConstants.ComponentsSegment + reference.Type.GetDisplayName() + "/" + reference.Id;
 
                 uriLocation = useExternal
                     ? Workspace?.GetDocumentId(reference.ExternalResource)?.OriginalString + relativePath

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -23,11 +23,28 @@ public class OpenApiOperation : IOpenApiSerializable, IOpenApiExtensible, IOpenA
         /// </summary>
         public const bool DeprecatedDefault = false;
 
+        private HashSet<OpenApiTagReference>? _tags;
         /// <summary>
         /// A list of tags for API documentation control.
         /// Tags can be used for logical grouping of operations by resources or any other qualifier.
         /// </summary>
-        public IList<OpenApiTagReference>? Tags { get; set; } = [];
+        public ISet<OpenApiTagReference>? Tags 
+        { 
+            get
+            {
+                return _tags;
+            }
+            set
+            {
+                if (value is null)
+                {
+                    return;
+                }
+                _tags = value is HashSet<OpenApiTagReference> tags && tags.Comparer is OpenApiTagComparer ?
+                        tags :
+                        new HashSet<OpenApiTagReference>(value, OpenApiTagComparer.Instance);
+            }
+        }
 
         /// <summary>
         /// A short summary of what the operation does.
@@ -123,7 +140,7 @@ public OpenApiOperation() { }
         public OpenApiOperation(OpenApiOperation operation)
         {
             Utils.CheckArgumentNull(operation);
-            Tags = operation.Tags != null ? new List<OpenApiTagReference>(operation.Tags) : null;
+            Tags = operation.Tags != null ? new HashSet<OpenApiTagReference>(operation.Tags) : null;
             Summary = operation.Summary ?? Summary;
             Description = operation.Description ?? Description;
             ExternalDocs = operation.ExternalDocs != null ? new(operation.ExternalDocs) : null;

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

@@ -21,7 +21,7 @@ public override OpenApiTag Target
         {
             get
             {
-                return Reference.HostDocument?.Tags.FirstOrDefault(t => StringComparer.Ordinal.Equals(t.Name, Reference.Id));
+                return Reference.HostDocument?.Tags?.FirstOrDefault(t => OpenApiTagComparer.StringComparer.Equals(t.Name, Reference.Id));
             }
         }
 

src/Microsoft.OpenApi/OpenApiTagComparer.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.OpenApi.Models.Interfaces;
+
+namespace Microsoft.OpenApi;
+
+#nullable enable
+/// <summary>
+/// This comparer is used to maintain a globally unique list of tags encountered
+/// in a particular OpenAPI document.
+/// </summary>
+internal sealed class OpenApiTagComparer : IEqualityComparer<IOpenApiTag>
+{
+    private static readonly Lazy<OpenApiTagComparer> _lazyInstance = new(() => new OpenApiTagComparer());
+    /// <summary>
+    /// Default instance for the comparer.
+    /// </summary>
+    internal static OpenApiTagComparer Instance { get => _lazyInstance.Value; }
+
+    /// <inheritdoc/>
+    public bool Equals(IOpenApiTag? x, IOpenApiTag? y)
+    {
+        if (x is null && y is null)
+        {
+            return true;
+        }
+        if (x is null || y is null)
+        {
+            return false;
+        }
+        if (ReferenceEquals(x, y))
+        {
+            return true;
+        }
+        return StringComparer.Equals(x.Name, y.Name);
+    }
+
+    // Tag comparisons are case-sensitive by default. Although the OpenAPI specification
+    // only outlines case sensitivity for property names, we extend this principle to
+    // property values for tag names as well.
+    // See https://spec.openapis.org/oas/v3.1.0#format.
+    internal static readonly StringComparer StringComparer = StringComparer.Ordinal;
+
+    /// <inheritdoc/>
+    public int GetHashCode(IOpenApiTag obj) => string.IsNullOrEmpty(obj?.Name) ? 0 : StringComparer.GetHashCode(obj!.Name);
+}
+#nullable restore

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

@@ -104,7 +104,7 @@ internal static partial class OpenApiV2Deserializer
                 }
             },
             {"security", (o, n, _) => o.SecurityRequirements = n.CreateList(LoadSecurityRequirement, o)},
-            {"tags", (o, n, _) => o.Tags = n.CreateList(LoadTag, o)},
+            {"tags", (o, n, _) => { if (n.CreateList(LoadTag, o) is {Count:> 0} tags) {o.Tags = new HashSet<OpenApiTag>(tags, OpenApiTagComparer.Instance); } } },
             {"externalDocs", (o, n, _) => o.ExternalDocs = LoadExternalDocs(n, o)}
         };
 

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

@@ -23,10 +23,12 @@ internal static partial class OpenApiV2Deserializer
             new()
             {
                 {
-                    "tags", (o, n, doc) => o.Tags = n.CreateSimpleList(
-                        (valueNode, doc) =>
-                            LoadTagByReference(
-                                valueNode.GetScalarValue(), doc), doc)
+                    "tags", (o, n, doc) => { 
+                        if (n.CreateSimpleList((valueNode, doc) => LoadTagByReference(valueNode.GetScalarValue(), doc), doc) is {Count: > 0} tags)
+                        {
+                            o.Tags = new HashSet<OpenApiTagReference>(tags, OpenApiTagComparer.Instance);
+                        }
+                    }
                 },
                 {
                     "summary",

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

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Reader.ParseNodes;
@@ -26,7 +27,7 @@ internal static partial class OpenApiV3Deserializer
             {"servers", (o, n, _) => o.Servers = n.CreateList(LoadServer, o)},
             {"paths", (o, n, _) => o.Paths = LoadPaths(n, o)},
             {"components", (o, n, _) => o.Components = LoadComponents(n, o)},
-            {"tags", (o, n, _) => o.Tags = n.CreateList(LoadTag, o) },
+            {"tags", (o, n, _) => { if (n.CreateList(LoadTag, o) is {Count:> 0} tags) {o.Tags = new HashSet<OpenApiTag>(tags, OpenApiTagComparer.Instance); } } },
             {"externalDocs", (o, n, _) => o.ExternalDocs = LoadExternalDocs(n, o)},
             {"security", (o, n, _) => o.SecurityRequirements = n.CreateList(LoadSecurityRequirement, o)}
         };

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

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Models.References;
@@ -19,10 +20,12 @@ internal static partial class OpenApiV3Deserializer
             new()
             {
                 {
-                    "tags", (o, n, doc) => o.Tags = n.CreateSimpleList(
-                        (valueNode, doc) =>
-                            LoadTagByReference(
-                                valueNode.GetScalarValue(), doc), doc)
+                    "tags", (o, n, doc) => { 
+                        if (n.CreateSimpleList((valueNode, doc) => LoadTagByReference(valueNode.GetScalarValue(), doc), doc) is {Count: > 0} tags)
+                        {
+                            o.Tags = new HashSet<OpenApiTagReference>(tags, OpenApiTagComparer.Instance);
+                        }
+                    }
                 },
                 {
                     "summary",

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

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Reader.ParseNodes;
@@ -24,7 +25,7 @@ internal static partial class OpenApiV31Deserializer
             {"paths", (o, n, _) => o.Paths = LoadPaths(n, o)},
             {"webhooks", (o, n, _) => o.Webhooks = n.CreateMap(LoadPathItem, o)},
             {"components", (o, n, _) => o.Components = LoadComponents(n, o)},
-            {"tags", (o, n, _) => o.Tags = n.CreateList(LoadTag, o) },
+            {"tags", (o, n, _) => { if (n.CreateList(LoadTag, o) is {Count:> 0} tags) {o.Tags = new HashSet<OpenApiTag>(tags, OpenApiTagComparer.Instance); } } },
             {"externalDocs", (o, n, _) => o.ExternalDocs = LoadExternalDocs(n, o)},
             {"security", (o, n, _) => o.SecurityRequirements = n.CreateList(LoadSecurityRequirement, o)}
         };

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

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Microsoft.OpenApi.Extensions;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Models.References;
@@ -16,9 +17,12 @@ internal static partial class OpenApiV31Deserializer
             new()
             {
                 {
-                    "tags", (o, n, doc) => o.Tags = n.CreateSimpleList(
-                        (valueNode, doc) =>
-                            LoadTagByReference(valueNode.GetScalarValue(), doc), doc)
+                    "tags", (o, n, doc) => { 
+                        if (n.CreateSimpleList((valueNode, doc) => LoadTagByReference(valueNode.GetScalarValue(), doc), doc) is {Count: > 0} tags)
+                        {
+                            o.Tags = new HashSet<OpenApiTagReference>(tags, OpenApiTagComparer.Instance);
+                        }
+                    }
                 },
                 {
                     "summary", (o, n, _) =>

src/Microsoft.OpenApi/Services/OpenApiFilterService.cs

@@ -363,11 +363,11 @@ private static void ValidateFilters(IDictionary<string, List<string>> requestUrl
             if (tagsArray.Length == 1)
             {
                 var regex = new Regex(tagsArray[0]);
-                return (_, _, operation) => operation.Tags.Any(tag => regex.IsMatch(tag.Name));
+                return (_, _, operation) => operation.Tags?.Any(tag => regex.IsMatch(tag.Name)) ?? false;
             }
             else
             {
-                return (_, _, operation) => operation.Tags.Any(tag => tagsArray.Contains(tag.Name));
+                return (_, _, operation) => operation.Tags?.Any(tag => tagsArray.Contains(tag.Name)) ?? false;
             }
         }
 

src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs

@@ -309,14 +309,14 @@ public virtual void Visit(IOpenApiExample example)
         /// <summary>
         /// Visits list of <see cref="OpenApiTag"/>
         /// </summary>
-        public virtual void Visit(IList<OpenApiTag> openApiTags)
+        public virtual void Visit(ISet<OpenApiTag> openApiTags)
         {
         }
 
         /// <summary>
         /// Visits list of <see cref="OpenApiTagReference"/>
         /// </summary>
-        public virtual void Visit(IList<OpenApiTagReference> openApiTags)
+        public virtual void Visit(ISet<OpenApiTagReference> openApiTags)
         {
         }
 

src/Microsoft.OpenApi/Services/OpenApiWalker.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text.Json.Nodes;
 using Microsoft.OpenApi.Any;
 using Microsoft.OpenApi.Extensions;
@@ -60,7 +61,7 @@
         /// <summary>
         /// Visits list of <see cref="OpenApiTag"/> and child objects
         /// </summary>
-        internal void Walk(IList<OpenApiTag> tags)
+        internal void Walk(ISet<OpenApiTag> tags)
         {
             if (tags == null)
             {
@@ -70,19 +71,20 @@
             _visitor.Visit(tags);
 
             // Visit tags
             if (tags != null)
             {
-                for (var i = 0; i < tags.Count; i++)
+                var tagsAsArray = tags.ToArray();
+                for (var i = 0; i < tagsAsArray.Length; i++)
                 {
-                    Walk(i.ToString(), () => Walk(tags[i]));
+                    Walk(i.ToString(), () => Walk(tagsAsArray[i]));
                 }
             }
         }
 
         /// <summary>
         /// Visits list of <see cref="OpenApiTagReference"/> and child objects
         /// </summary>
-        internal void Walk(IList<OpenApiTagReference> tags)
+        internal void Walk(ISet<OpenApiTagReference> tags)
         {
             if (tags == null)
             {
@@ -92,11 +94,12 @@
             _visitor.Visit(tags);
 
             // Visit tags
             if (tags != null)
             {
-                for (var i = 0; i < tags.Count; i++)
+                var referencesAsArray = tags.ToArray();
+                for (var i = 0; i < referencesAsArray.Length; i++)
                 {
-                    Walk(i.ToString(), () => Walk(tags[i]));
+                    Walk(i.ToString(), () => Walk(referencesAsArray[i]));
                 }
             }
         }
@@ -130,7 +133,7 @@
         /// <summary>
         /// Visits <see cref="OpenApiComponents"/> and child objects
         /// </summary>
         internal void Walk(OpenApiComponents? components)
         {
             if (components == null)
             {
@@ -266,7 +269,7 @@
             _visitor.Visit(paths);
 
             // Visit Paths
             if (paths != null)
             {
                 foreach (var pathItem in paths)
                 {
@@ -291,7 +294,7 @@
             _visitor.Visit(webhooks);
 
             // Visit Webhooks
             if (webhooks != null)
             {
                 foreach (var pathItem in webhooks)
                 {
@@ -299,7 +302,7 @@
                     Walk(pathItem.Key, () => Walk(pathItem.Value));// JSON Pointer uses ~1 as an escape character for /
                     _visitor.CurrentKeys.Path = null;
                 }
             };
         }
 
         /// <summary>
@@ -423,7 +426,7 @@
 
             _visitor.Visit(callback);
 
             if (callback != null)
             {
                 foreach (var item in callback.PathItems)
                 {
@@ -460,7 +463,7 @@
                 return;
             }
 
             if (tag is IOpenApiReferenceHolder openApiReferenceHolder)
             {
                 Walk(openApiReferenceHolder);
             }
@@ -1213,7 +1216,7 @@
                 case OpenApiServer e: Walk(e); break;
                 case OpenApiServerVariable e: Walk(e); break;
                 case OpenApiTag e: Walk(e); break;
-                case IList<OpenApiTag> e: Walk(e); break;
+                case ISet<OpenApiTag> e: Walk(e); break;
                 case IOpenApiExtensible e: Walk(e); break;
                 case IOpenApiExtension e: Walk(e); break;
             }

test/Microsoft.OpenApi.Hidi.Tests/UtilityFiles/OpenApiDocumentMock.cs

@@ -629,7 +629,7 @@ public static OpenApiDocument CreateOpenApiDocument()
                         }
                     }
                 },
-                Tags = new List<OpenApiTag>
+                Tags = new HashSet<OpenApiTag>
                 {
                     new()
                     {
@@ -678,18 +678,18 @@ public static OpenApiDocument CreateOpenApiDocument()
                     }
                 }
             };
-            document.Paths[getTeamsActivityByPeriodPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("reports.Functions", document));
-            document.Paths[getTeamsActivityByDatePath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("reports.Functions", document));
-            document.Paths[usersPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("users.user", document));
-            document.Paths[usersByIdPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("users.user", document));
-            document.Paths[usersByIdPath].Operations[OperationType.Patch].Tags!.Add(new OpenApiTagReference("users.user", document));
-            document.Paths[messagesByIdPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("users.message", document));
-            document.Paths[administrativeUnitRestorePath].Operations[OperationType.Post].Tags!.Add(new OpenApiTagReference("administrativeUnits.Actions", document));
-            document.Paths[logoPath].Operations[OperationType.Put].Tags!.Add(new OpenApiTagReference("applications.application", document));
-            document.Paths[securityProfilesPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("security.hostSecurityProfile", document));
-            document.Paths[communicationsCallsKeepAlivePath].Operations[OperationType.Post].Tags!.Add(new OpenApiTagReference("communications.Actions", document));
-            document.Paths[eventsDeltaPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("groups.Functions", document));
-            document.Paths[refPath].Operations[OperationType.Get].Tags!.Add(new OpenApiTagReference("applications.directoryObject", document));
+            document.Paths[getTeamsActivityByPeriodPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("reports.Functions", document)};
+            document.Paths[getTeamsActivityByDatePath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("reports.Functions", document)};
+            document.Paths[usersPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.user", document)};
+            document.Paths[usersByIdPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.user", document)};
+            document.Paths[usersByIdPath].Operations[OperationType.Patch].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.user", document)};
+            document.Paths[messagesByIdPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("users.message", document)};
+            document.Paths[administrativeUnitRestorePath].Operations[OperationType.Post].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("administrativeUnits.Actions", document)};
+            document.Paths[logoPath].Operations[OperationType.Put].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("applications.application", document)};
+            document.Paths[securityProfilesPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("security.hostSecurityProfile", document)};
+            document.Paths[communicationsCallsKeepAlivePath].Operations[OperationType.Post].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("communications.Actions", document)};
+            document.Paths[eventsDeltaPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("groups.Functions", document)};
+            document.Paths[refPath].Operations[OperationType.Get].Tags = new HashSet<OpenApiTagReference> {new OpenApiTagReference("applications.directoryObject", document)};
             ((OpenApiSchema)document.Paths[usersPath].Operations[OperationType.Get].Responses!["200"].Content[applicationJsonMediaType].Schema!.Properties["value"]).Items = new OpenApiSchemaReference("microsoft.graph.user", document);
             document.Paths[usersByIdPath].Operations[OperationType.Get].Responses!["200"].Content[applicationJsonMediaType].Schema = new OpenApiSchemaReference("microsoft.graph.user", document);
             document.Paths[messagesByIdPath].Operations[OperationType.Get].Responses!["200"].Content[applicationJsonMediaType].Schema = new OpenApiSchemaReference("microsoft.graph.message", document);