Update on "Replace pytree_assert with production pytree_check. Remove pytree_unreachable"

When handling untrusted input, it's not appropriate to use debug-only checks; we should be checking in prod as these are not programmer errors. pytree_unreachable was similarly being used for input validation.

Differential Revision: [D68166301](https://our.internmc.facebook.com/intern/diff/D68166301/)

[ghstack-poisoned]

Author: swolchok

extension/pytree/pybindings.cpp

@@ -145,7 +145,8 @@ class PyTree {
           } else if (py::isinstance<py::int_>(key)) {
             s.key(i) = py::cast<int32_t>(key);
           } else {
-            throw std::runtime_err("invalid key in pytree dict; must be int or string");
+            throw std::runtime_err(
+                "invalid key in pytree dict; must be int or string");
           }
 
           flatten_internal(dict[key], leaves, s[i]);
@@ -224,7 +225,8 @@ class PyTree {
               case Key::Kind::Str:
                 return py::cast(key.as_str()).release();
               default:
-                throw std::runtime_error("invalid key in pytree dict; must be int or string");
+                throw std::runtime_error(
+                    "invalid key in pytree dict; must be int or string");
             }
           }();
           dict[py_key] = unflatten_internal(spec[i], leaves_it);

extension/pytree/test/test_pytree.cpp

@@ -11,13 +11,28 @@
 #include <gtest/gtest.h>
 #include <string>
 
+using ::executorch::extension::pytree::arr;
 using ::executorch::extension::pytree::ContainerHandle;
 using ::executorch::extension::pytree::Key;
 using ::executorch::extension::pytree::Kind;
 using ::executorch::extension::pytree::unflatten;
 
 using Leaf = int32_t;
 
+TEST(PyTreeTest, ArrBasic) {
+  arr<int> x(5);
+  ASSERT_EQ(x.size(), 5);
+  EXPECT_THROW(x.at(5), std::out_of_range);
+  for (int ii = 0; ii < x.size(); ++ii) {
+    x[ii] = 2 * ii;
+  }
+  int idx = 0;
+  for (const auto item : x) {
+    EXPECT_EQ(item, 2 * idx);
+    ++idx;
+  }
+}
+
 TEST(PyTreeTest, List) {
   Leaf items[2] = {11, 12};
   std::string spec = "L2#1#1($,$)";