[tools/tests] Fix bug in 'link all' test and the resulting regression…

… that showed up in code.

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
(dotnet/runtime#84118).

tests/linker/ios/link all/LinkAllTest.cs

@@ -275,8 +275,9 @@ public void DetectPlatform ()
  [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

tools/linker/CoreRemoveAttributes.cs

@@ -49,6 +49,10 @@ protected override bool IsRemovedAttribute (CustomAttribute attribute)
  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 @@ protected override void WillRemoveAttribute (ICustomAttributeProvider provider,
  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":