[Concurrency] NonisolatedNonsendingByDefault: Don't attempt to migrate swift-testing test cases

The execution of these functions is controlled by the testing
framework and it's okay if their behavior changes when the feature
flag is enabled.

Resolves: rdar://152687527

Author: xedin

lib/Sema/NonisolatedNonsendingByDefaultMigration.cpp

@@ -21,6 +21,7 @@
 #include "swift/AST/Decl.h"
 #include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/Expr.h"
+#include "swift/AST/Module.h"
 #include "swift/AST/ParameterList.h"
 #include "swift/AST/TypeRepr.h"
 #include "swift/Basic/Assertions.h"
@@ -55,6 +56,27 @@ class NonisolatedNonsendingByDefaultMigrationTarget {
   /// behavior.
   void diagnose() const;
 };
+
+/// Determine whether the decl represents a test function that is
+/// annotated with `@Test` macro from the swift-testing framework.
+/// Such functions should be exempt from the migration because their
+/// execution is controlled by the framework and the change in
+/// behavior doesn't affect them.
+static bool isSwiftTestingTestFunction(ValueDecl *decl) {
+  if (!isa<FuncDecl>(decl))
+    return false;
+
+  return llvm::any_of(decl->getAttrs(), [&decl](DeclAttribute *attr) {
+    auto customAttr = dyn_cast<CustomAttr>(attr);
+    if (!customAttr)
+      return false;
+
+    auto *macro = decl->getResolvedMacro(customAttr);
+    return macro && macro->getBaseIdentifier().is("Test") &&
+           macro->getParentModule()->getName().is("Testing");
+  });
+}
+
 } // end anonymous namespace
 
 void NonisolatedNonsendingByDefaultMigrationTarget::diagnose() const {
@@ -78,6 +100,11 @@ void NonisolatedNonsendingByDefaultMigrationTarget::diagnose() const {
       return;
     }
 
+    // `@Test` test-case have special semantics.
+    if (isSwiftTestingTestFunction(decl)) {
+      return;
+    }
+
     // If the attribute cannot appear on this kind of declaration, we can't
     // diagnose it.
     if (!DeclAttribute::canAttributeAppearOnDecl(DeclAttrKind::Concurrent,