Fix: Use route parameter metadata to correctly mark catch-all parameters as optional

Previously, ApiExplorer marked all parameters as optional if the route template contained a catch-all marker ("{**"). This update refines the logic by leveraging ApiParameterContext.RouteParameters and the IsCatchAll flag to identify and mark only the catch-all parameter as optional. This change aligns the API metadata with the actual routing semantics and addresses dotnet#60392.

Author: mapedersen

src/Mvc/Mvc.ApiExplorer/src/DefaultApiDescriptionProvider.cs

@@ -317,9 +317,12 @@ internal static void ProcessIsRequired(ApiParameterContext context, MvcOptions m
 
             if (parameter.Source == BindingSource.Path && parameter.RouteInfo != null)
             {
-                // If the route template contains a catch-all parameter marker ("{**"), treat it as optional.
-                var template = context.ActionDescriptor.AttributeRouteInfo?.Template;
-                if (!string.IsNullOrEmpty(template) && template.Contains("{**"))
+                // Locate the corresponding route parameter metadata.
+                var routeParam = context.RouteParameters
+                    .FirstOrDefault(rp => string.Equals(rp.Name, parameter.Name, StringComparison.OrdinalIgnoreCase));
+
+                // If the parameter is defined as a catch-all, mark it as optional.
+                if (routeParam != null && routeParam.IsCatchAll)
                 {
                     parameter.IsRequired = false;
                 }

src/Mvc/Mvc.ApiExplorer/test/DefaultApiDescriptionProviderTest.cs

@@ -33,20 +33,33 @@ namespace Microsoft.AspNetCore.Mvc.Description;
 public class DefaultApiDescriptionProviderTest
 {
     [Fact]
-    public void CatchAllParameter_IsReportedAsOptional()
+    public void OnlyCatchAllParameter_IsReportedAsOptional()
     {
-        // Arrange: Create an action descriptor with a catch-all route template.
+        // Arrange: Create an action descriptor with a multi-parameter route template.
         var action = CreateActionDescriptor();
-        action.AttributeRouteInfo = new AttributeRouteInfo { Template = "{**catchAllParameter}" };
+        action.AttributeRouteInfo = new AttributeRouteInfo
+        {
+            Template = "/products/{category}/items/{group}/inventory/{**any}"
+        };
 
         // Act: Get the API descriptions using the existing helper.
         var descriptions = GetApiDescriptions(action);
 
-        // Assert: There should be one description, with one parameter named "catchAllParameter"
-        // and its IsRequired property should be false.
+        // Assert: Only the 'any' parameter should be optional.
         var description = Assert.Single(descriptions);
-        var parameter = Assert.Single(description.ParameterDescriptions, p => p.Name == "catchAllParameter");
-        Assert.False(parameter.IsRequired);
+        var categoryParameter = Assert.Single(description.ParameterDescriptions,
+            p => string.Equals(p.Name, "category", StringComparison.OrdinalIgnoreCase));
+        var groupParameter = Assert.Single(description.ParameterDescriptions,
+            p => string.Equals(p.Name, "group", StringComparison.OrdinalIgnoreCase));
+        var anyParameter = Assert.Single(description.ParameterDescriptions,
+            p => string.Equals(p.Name, "any", StringComparison.OrdinalIgnoreCase));
+
+        // The non-catch-all parameters should be required.
+        Assert.True(categoryParameter.IsRequired);
+        Assert.True(groupParameter.IsRequired);
+
+        // The catch-all parameter should be optional.
+        Assert.False(anyParameter.IsRequired);
     }
 
     [Fact]