From a54ab5c42a5aa6076b1b369b092049f4873eb9f0 Mon Sep 17 00:00:00 2001
From: Rolf Bjarne Kvinge <rolf@xamarin.com>
Date: Tue, 11 Apr 2023 20:12:35 +0200
Subject: [PATCH] [tools/tests] Fix bug in 'link all' test and the resulting
 regression that showed up in code. (#18016)

There's a 'link all' test that's verifying that the IntroducedAttribute is
linked away. It does so by verifying that the linked app doesn't have a
'IntroducedAttribute' type - but the test was constructing the fully qualified
type name to look for incorrectly:

    ObjCRuntime.IntroducedAttribute, , Microsoft.iOS

Note the double comma: that meant we wouldn't find the type, even if it wasn't linked away.

The fix is easy (use a single comma), with one caveat (don't use a constant
string, because the linker sees the reference to
"ObjCRuntime.IntroducedAttribute" and _helpfully_ preserves it, exactly what
we don't want), but it revealed that the tested behavior regressed: a fully
linked app wouldn't link away the IntroducedAttribute.

So a fix is also needed: properly remove TVAttribute, WatchAttribute and
MacCatalystAttribute, which are subclasses of IntroducedAttribute (and what
would make the linker keep IntroducedAttribute).

Interestingly this showed up because of a bug in the runtime, where parsing
the invalid assembly name would now throw an exception
(https://github.com/dotnet/runtime/issues/84118).
---
 tests/linker/ios/link all/LinkAllTest.cs | 5 +++--
 tools/linker/CoreRemoveAttributes.cs     | 8 ++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tests/linker/ios/link all/LinkAllTest.cs b/tests/linker/ios/link all/LinkAllTest.cs
index 608a598ea7..03c2e65dd6 100644
--- a/tests/linker/ios/link all/LinkAllTest.cs	
+++ b/tests/linker/ios/link all/LinkAllTest.cs	
@@ -275,8 +275,9 @@ namespace LinkAll {
 		[ThreadSafe]
 		public void RemovedAttributes ()
 		{
-			const string prefix = NamespacePrefix;
-			const string suffix = ", " + AssemblyName;
+			// Don't use constants here, because the linker can see what we're trying to do and keeps what we're verifying has been removed.
+			string prefix = NamespacePrefix;
+			string suffix = AssemblyName;
 
 			// since we're linking the attributes will NOT be available - even if they are used
 #if !XAMCORE_3_0
diff --git a/tools/linker/CoreRemoveAttributes.cs b/tools/linker/CoreRemoveAttributes.cs
index 02cbb86cbe..2412aa1ab0 100644
--- a/tools/linker/CoreRemoveAttributes.cs
+++ b/tools/linker/CoreRemoveAttributes.cs
@@ -49,6 +49,10 @@ namespace Xamarin.Linker {
 			case "NoMacAttribute":
 			case "NoTVAttribute":
 			case "NoWatchAttribute":
+			// special subclasses of IntroducedAttribute
+			case "TVAttribute":
+			case "MacCatalystAttribute":
+			case "WatchAttribute":
 				return attr_type.Namespace == Namespaces.ObjCRuntime;
 			// special subclasses of IntroducedAttribute
 			case "iOSAttribute":
@@ -73,6 +77,10 @@ namespace Xamarin.Linker {
 				case "AvailabilityBaseAttribute":   // base type for IntroducedAttribute and DeprecatedAttribute (could be in user code)
 				case "DeprecatedAttribute":
 				case "IntroducedAttribute":
+				// they are subclasses of ObjCRuntime.IntroducedAttribute
+				case "TVAttribute":
+				case "MacCatalystAttribute":
+				case "WatchAttribute":
 					LinkContext.StoreCustomAttribute (provider, attribute, "Availability");
 					break;
 				case "AdoptsAttribute":