Fix resolution of the external dependencies.

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Utilities/ExternalTypeReferenceResolver.cs

@@ -5,13 +5,15 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.TypeSpec.Generator.Input;
 using NuGet.Configuration;
+using NuGet.Versioning;
 
 namespace Microsoft.TypeSpec.Generator.Utilities
 {
@@ -238,10 +240,30 @@ private static async Task<ResolutionResult> ResolveResultAsync(InputExternalType
             {
                 try
                 {
-                    var resolvedVersion = !string.IsNullOrEmpty(external.MinVersion)
-                        ? external.MinVersion!
-                        : await NugetPackageResolver.ResolveLatestPackageVersion(external.Package!, nugetSettings);
-
+                    string? resolvedVersion;
+                    // Search for the compatible version.
+                    if (!string.IsNullOrEmpty(external.MinVersion))
+                    {
+                        // If min version was provided, we
+                        // 1. Search if it is in our repositories;
+                        // 2. Get the latest one if it is not.
+                        // 3. If our version is a pre release, include pre released versions in our search.
+                        NuGetVersion minVersion = new(external.MinVersion);
+                        IList<NuGetVersion> versions = await NugetPackageResolver.GetAllVersions(external.Package!, nugetSettings, allowPrerelease: minVersion.IsPrerelease);
+                        if (versions.Any(x => x == minVersion))
+                        {
+                            resolvedVersion = external.MinVersion;
+                        }
+                        else
+                        {
+                            resolvedVersion = versions.Max()?.ToString();
+                        }
+                    }
+                    else
+                    {
+                        // If min version was not provided, get the latest stable version.
+                        resolvedVersion = await NugetPackageResolver.ResolveLatestPackageVersion(external.Package!, nugetSettings);
+                    }
                     if (!string.IsNullOrEmpty(resolvedVersion))
                     {
                         var downloader = new NugetPackageDownloader(external.Package!, resolvedVersion!, null, nugetSettings);

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Utilities/NugetPackageResolver.cs

@@ -10,6 +10,7 @@
 using System.Threading.Tasks;
 using NuGet.Configuration;
 using NuGet.Frameworks;
+using NuGet.Packaging;
 using NuGet.Protocol;
 using NuGet.Protocol.Core.Types;
 using NuGet.Repositories;
@@ -202,6 +203,28 @@ private static NuGetFramework ResolveCurrentFramework()
             return null;
         }
 
+        public static async Task<IList<NuGetVersion>> GetAllVersions(string packageName, ISettings nugetSettings, bool allowPrerelease)
+        {
+            HashSet<NuGetVersion> versions = [];
+            var sources = SettingsUtility.GetEnabledSources(nugetSettings);
+            using var cacheContext = new SourceCacheContext();
+            foreach (var source in sources)
+            {
+                try
+                {
+                    var repository = Repository.Factory.GetCoreV3(source.Source);
+                    var resource = await repository.GetResourceAsync<FindPackageByIdResource>();
+                    IEnumerable<NuGetVersion> versionsFromOneRepo = (await resource.GetAllVersionsAsync(packageName, cacheContext, NuGet.Common.NullLogger.Instance, CancellationToken.None)).Where(v => !v.IsPrerelease || allowPrerelease);
+                    versions.AddRange(versionsFromOneRepo);
+                }
+                catch
+                {
+                    // Skip failed source.
+                }
+            }
+            return [..versions];
+        }
+
         /// <summary>
         /// Queries the configured NuGet feeds for the latest stable version of <paramref name="packageName"/>.
         /// When <paramref name="minVersion"/> is provided, the latest stable version greater than or equal to it