Preserve types for serialization (#1932)

* Preserve types for XML serializer

* Move TypePreserve.All

* Add doc about serialization handling

* Adjust comments

* Remove dataflow type discovery

* Add more tests, update doc

* Add logic for DataContractSerializer

* Remove IsActiveFor check

* Fix comments

* Update docs

* PR feedback
- Remove redundant usings
- Make MarkSubStepsDispatcher non-abstract, make ctor public
- PreserveSerialization -> PreserveSerializationSubStep
- SerializationHelper -> SerializationMarker

* Update heuristics to be less conservative

Instead of trying to conservatively match the xamarin-android behavior,
this now does something more "correct" without building in too much
serializer-specific logic. Specifically:
- Don't preserve methods
- Don't preserve static members
- Don't preserve private members

* Only scan types that are already marked

* Fix test

* Activate serialization logic only for ctor calls

With this change the serialization heuristics will mark types only if
there was a call to a relevant serialization constructor.

* PR feedback

Update docs

* PR feedback

Change flag to --disable-serialization-discovery, and add a test
to check that disabling works as expected.

* Add missing changes

* Update docs/serialization.md

Co-authored-by: Vitek Karas <vitek.karas@microsoft.com>

* Update docs/serialization.md

Co-authored-by: Vitek Karas <vitek.karas@microsoft.com>

* Update src/linker/Linker.Steps/DiscoverSerializationHandler.cs

Co-authored-by: Vitek Karas <vitek.karas@microsoft.com>

* Update src/linker/Linker.Steps/DiscoverSerializationHandler.cs

Co-authored-by: Vitek Karas <vitek.karas@microsoft.com>

* PR feedback

To ensure private attributed members get marked, this changes the "root"
tracking to track members rather than types. Marking a root member for
serialization will now ensure that the member and its type
(for fields/properties) also get marked recursively.
Similar behavior applies for static members, methods, and events.

Also address other feedback:
- Update docs to describe .ctor-based activation
- Clarify kept vs considered root
- RecursiveType -> SerializedRecursiveType
- Add comment about array type handling

* Handle DataContractJsonSerializer

* Mention DataContractJsonSerializer in docs

Co-authored-by: Vitek Karas <vitek.karas@microsoft.com>

2 files changed, 11 insertions, 0 deletions

diff --git a/test/Mono.Linker.Tests/TestCases/TestDatabase.cs b/test/Mono.Linker.Tests/TestCases/TestDatabase.cs
index c4d06e598..73e5ed671 100644
--- a/test/Mono.Linker.Tests/TestCases/TestDatabase.cs
+++ b/test/Mono.Linker.Tests/TestCases/TestDatabase.cs
@@ -166,6 +166,11 @@ namespace Mono.Linker.Tests.TestCases
 			return NUnitCasesBySuiteName ("Sealer");
 		}
 
+		public static IEnumerable<TestCaseData> SerializationTests ()
+		{
+			return NUnitCasesBySuiteName ("Serialization");
+		}
+
 		public static IEnumerable<TestCaseData> SubstitutionsTests ()
 		{
 			return NUnitCasesBySuiteName ("Substitutions");
diff --git a/test/Mono.Linker.Tests/TestCases/TestSuites.cs b/test/Mono.Linker.Tests/TestCases/TestSuites.cs
index 6edb4ac4b..ae2d45090 100644
--- a/test/Mono.Linker.Tests/TestCases/TestSuites.cs
+++ b/test/Mono.Linker.Tests/TestCases/TestSuites.cs
@@ -217,6 +217,12 @@ namespace Mono.Linker.Tests.TestCases
 			Run (testCase);
 		}
 
+		[TestCaseSource (typeof (TestDatabase), nameof (TestDatabase.SerializationTests))]
+		public void SerializationTests (TestCase testCase)
+		{
+			Run (testCase);
+		}
+
 
 		[TestCaseSource (typeof (TestDatabase), nameof (TestDatabase.ExtensibilityTests))]
 		public void ExtensibilityTests (TestCase testCase)