Support multiple calls to WithTags in WithOpenApi

src/OpenApi/src/OpenApiGenerator.cs

@@ -328,7 +328,23 @@ private static void GenerateDefaultResponses(Dictionary<int, (Type?, MediaTypeCo
 
     private List<OpenApiTag> GetOperationTags(MethodInfo methodInfo, EndpointMetadataCollection metadata)
     {
-        var tags = metadata.GetMetadata<ITagsMetadata>();
+        var metadataList = metadata.GetOrderedMetadata<ITagsMetadata>();
+
+        if (metadataList.Count > 0)
+        {
+            var tags = new List<OpenApiTag>();
+
+            foreach (var metadataItem in metadataList)
+            {
+                foreach (var tag in metadataItem.Tags)
+                {
+                    tags.Add(new OpenApiTag() { Name = tag });
+                }
+            }
+
+            return tags;
+        }
+
         string controllerName;
 
         if (methodInfo.DeclaringType is not null && !TypeHelper.IsCompilerGeneratedType(methodInfo.DeclaringType))
@@ -342,9 +358,7 @@ private List<OpenApiTag> GetOperationTags(MethodInfo methodInfo, EndpointMetadat
             controllerName = _environment?.ApplicationName ?? string.Empty;
         }
 
-        return tags is not null
-            ? tags.Tags.Select(tag => new OpenApiTag() { Name = tag }).ToList()
-            : new List<OpenApiTag>() { new OpenApiTag() { Name = controllerName } };
+        return new List<OpenApiTag>() { new OpenApiTag() { Name = controllerName } };
     }
 
     private List<OpenApiParameter> GetOpenApiParameters(MethodInfo methodInfo, EndpointMetadataCollection metadata, RoutePattern pattern, bool disableInferredBody)

src/OpenApi/test/OpenApiGeneratorTests.cs

@@ -4,6 +4,7 @@
 using System.Linq.Expressions;
 using System.Reflection;
 using System.Security.Claims;
+using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Mvc;
@@ -50,6 +51,23 @@ public void UsesApplicationNameAsOperationTagsIfNoDeclaringType()
         Assert.Equal(declaringTypeName, tag.Name);
     }
 
+    [Fact]
+    public void UsesTagsFromMultipleCallsToWithTags()
+    {
+        var testBuilder = new TestEndpointConventionBuilder();
+        var routeHandlerBuilder = new RouteHandlerBuilder(new[] { testBuilder });
+
+        routeHandlerBuilder
+            .WithTags("A")
+            .WithTags("B");
+
+        var operation = GetOpenApiOperation(() => { }, additionalMetadata: testBuilder.Metadata.ToArray());
+
+        Assert.Collection(operation.Tags,
+            tag => Assert.Equal("A", tag.Name),
+            tag => Assert.Equal("B", tag.Name));
+    }
+
     [Fact]
     public void ThrowsInvalidOperationExceptionGivenUnnamedParameter()
     {
@@ -923,4 +941,17 @@ private struct ArgumentListStruct
         public InferredJsonClass FromBody { get; set; }
         public HttpContext Context { get; set; }
     }
+
+    private class TestEndpointConventionBuilder : EndpointBuilder, IEndpointConventionBuilder
+    {
+        public void Add(Action<EndpointBuilder> convention)
+        {
+            convention(this);
+        }
+
+        public override Endpoint Build()
+        {
+            throw new NotImplementedException();
+        }
+    }
 }