Merge pull request swiftlang#23306 from aschwaighofer/fix_dynamic_replacement_undeclared_type_crash

Sema: Fix a crash when checking dynamic replacements on a non existing type

Author: aschwaighofer

lib/Sema/TypeCheckAttr.cpp

@@ -2005,8 +2005,9 @@ void lookupReplacedDecl(DeclName replacedDeclName,
   if (!typeCtx)
     typeCtx = cast<ExtensionDecl>(declCtxt->getAsDecl())->getExtendedNominal();
 
-  moduleScopeCtxt->lookupQualified({typeCtx}, replacedDeclName,
-                                   NL_QualifiedDefault, results);
+  if (typeCtx)
+    moduleScopeCtxt->lookupQualified({typeCtx}, replacedDeclName,
+                                     NL_QualifiedDefault, results);
 }
 
 /// Remove any argument labels from the interface type of the given value that

test/attr/dynamicReplacement.swift

@@ -46,3 +46,11 @@ extension K {
   @_dynamicReplacement(for: init(c:)) // expected-error{{replaced constructor 'init(c:)' is marked as convenience}})
   init(rc: Int) { }
 }
+
+extension undeclared { // expected-error{{use of undeclared type 'undeclared'}}
+  @_dynamicReplacement(for: property) // expected-error{{replaced accessor for 'property' could not be found}}
+  var replacement_property: Int { return 2 }
+
+  @_dynamicReplacement(for: func) // expected-error{{replaced function 'func' could not be found}}
+  func func2() -> Int { return 2 }
+}