Refused JSON contracts built by reflection and checked all of them in the trimmed build (#1152)

app/Tests/Serialization/JsonOptionsResolverTests.cs

@@ -0,0 +1,49 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using AIStudio.TrimSmokeTest;
+
+namespace AIStudio.Tests.Serialization;
+
+/// <summary>
+/// Checks that all options of the app get their contracts from source generation, never from reflection.
+/// </summary>
+/// <remarks>
+/// MWAIS0015 refuses options without a TypeInfoResolver while compiling, but cannot tell what the resolver does.
+/// Only contexts throw for a type they do not know. Any other resolver, e.g., a DefaultJsonTypeInfoResolver which
+/// a helper adds to the chain, builds the missing contract by reflection instead, and in a published build, the
+/// code it needs for that may be gone.
+/// </remarks>
+[TestFixture]
+public sealed class JsonOptionsResolverTests
+{
+    private static IEnumerable<TestCaseData> AllOptions()
+    {
+        TestHost.PrepareStaticState();
+        return AppJsonOptions.FindAll().Select(options => new TestCaseData(options.Value).SetArgDisplayNames(options.Key));
+    }
+
+    [TestCaseSource(nameof(AllOptions))]
+    public void TheOptionsResolveWithContextsOnly(JsonSerializerOptions options)
+    {
+        using (Assert.EnterMultipleScope())
+        {
+            Assert.That(options.TypeInfoResolverChain, Is.Not.Empty);
+            Assert.That(options.TypeInfoResolverChain, Is.All.InstanceOf<JsonSerializerContext>());
+        }
+    }
+
+    [Test]
+    public void FieldsAndPropertiesOfTheAppAreFound()
+    {
+        TestHost.PrepareStaticState();
+        var names = AppJsonOptions.FindAll().Keys.ToList();
+
+        using (Assert.EnterMultipleScope())
+        {
+            Assert.That(names, Does.Contain("SettingsManager.JSON_OPTIONS"));
+            Assert.That(names, Does.Contain("VisualBriefingJson.Canonical"));
+            Assert.That(names, Has.None.Contains("k__BackingField"));
+        }
+    }
+}