[interop] do not traverse type locs when IRGening clang decls from Swift

lib/IRGen/GenClangDecl.cpp

@@ -112,6 +112,10 @@ class ClangDeclFinder
     return true;
   }
 
+  // Do not traverse type locs, as they might contain expressions that reference
+  // code that should not be instantiated and/or emitted.
+  bool TraverseTypeLoc(clang::TypeLoc TL) { return true; }
+
   bool shouldVisitTemplateInstantiations() const { return true; }
   bool shouldVisitImplicitCode() const { return true; }
 };

test/Interop/Cxx/templates/Inputs/unevaluated-context.h

@@ -35,4 +35,27 @@ inline void initVector() {
   vv.push_back(0);
 }
 
+template <class T>
+class UseDeclVal {
+public:
+    UseDeclVal() {}
+
+    auto declTypeRet() const noexcept -> decltype(declval<T>().method()) {
+        return T().method();
+    }
+
+    inline int callMethod() const {
+        int x = declTypeRet();
+        return x;
+    }
+};
+
+struct StructWithMethod {
+    inline int method() {
+        return 42;
+    }
+};
+
+using UseDeclValStruct = UseDeclVal<StructWithMethod>;
+
 #endif // TEST_INTEROP_CXX_TEMPLATES_INPUTS_UNEVALUATED_CONTEXT_H

test/Interop/Cxx/templates/unevaluated-context.swift

@@ -9,6 +9,7 @@ var UnevaluatedTestSuite = TestSuite("UnevaluatedContext")
 
 UnevaluatedTestSuite.test("declval") {
   initVector()
+  let _ = UseDeclValStruct().callMethod()
 }
 
 runAllTests()