From 649f34ae24fc67ebb67def6a29ca80d40ef9e637 Mon Sep 17 00:00:00 2001
From: Thierry Treyer <ttreyer@fb.com>
Date: Wed, 10 Jan 2024 07:07:47 -0800
Subject: [PATCH 1/3] Fix static_assert failure for zero-length array

The recursive template implemented for `validate_size` does not support
incomplete types, like zero-length array.

By splitting the `validate_size` struct in two parts:
1. `validate_size_eq` that does the actual size check, and
2. `validate_size` that preserves the previous interface and inherit
   from `validate_size_eq`,
we get the same interface and feature than previously, but without the
recursive template that doesn't support incomplete types.
---
 oi/OITraceCode.cpp | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/oi/OITraceCode.cpp b/oi/OITraceCode.cpp
index a1009002..323c83e3 100644
--- a/oi/OITraceCode.cpp
+++ b/oi/OITraceCode.cpp
@@ -160,15 +160,14 @@ template <typename T, int32_t Id>
 struct DummyAllocator<T, 0, 1, Id>
     : DummyAllocatorBase<DummyAllocator, T, 0, 1, Id> {};
 
-template <typename Type, size_t ExpectedSize, size_t ActualSize = 0>
-struct validate_size {
+template <typename Type, size_t ExpectedSize, size_t ActualSize>
+struct validate_size_eq {
   static constexpr bool value = true;
   static_assert(ExpectedSize == ActualSize);
 };
 
 template <typename Type, size_t ExpectedSize>
-struct validate_size<Type, ExpectedSize>
-    : validate_size<Type, ExpectedSize, sizeof(Type)> {};
+struct validate_size : validate_size_eq<Type, ExpectedSize, sizeof(Type)> {};
 
 template <size_t ExpectedOffset, size_t ActualOffset>
 struct validate_offset {

From 4d8506d9ff4e2203e535d9634e3f0eaf4da887e0 Mon Sep 17 00:00:00 2001
From: Thierry Treyer <ttreyer@fb.com>
Date: Wed, 10 Jan 2024 08:14:30 -0800
Subject: [PATCH 2/3] Fix TreeBuilder processing of zero-length array

TreeBuilder did not consider a zero-length array like a container and
never read the array's sizeof stored in the data buffer, leading to a
mismatch between bytes written vs read out of the buffer.

Now, `TreeBuilder::isContainer` does consider zero-length array like
a container and properly consume all the object sizes in the buffer.
---
 oi/TreeBuilder.cpp | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/oi/TreeBuilder.cpp b/oi/TreeBuilder.cpp
index 954b293d..2ff1102a 100644
--- a/oi/TreeBuilder.cpp
+++ b/oi/TreeBuilder.cpp
@@ -378,9 +378,20 @@ uint64_t TreeBuilder::next() {
 }
 
 bool TreeBuilder::isContainer(const Variable& variable) {
-  return th->containerTypeMap.contains(variable.type) ||
-         (drgn_type_kind(variable.type) == DRGN_TYPE_ARRAY &&
-          drgn_type_length(variable.type) > 0);
+  if (th->containerTypeMap.contains(variable.type)) {
+    return true;
+  }
+
+  if (drgn_type_kind(variable.type) == DRGN_TYPE_ARRAY) {
+    /* CodeGen v1 does not consider zero-length array as containers,
+     * but CodeGen v2 does. This discrepancy is handled here.
+     * TODO: Cleanup this workaround once CodeGen v1 is gone. See #453
+     */
+    return config.features[Feature::TypeGraph] ||
+           drgn_type_length(variable.type) > 0;
+  }
+
+  return false;
 }
 
 bool TreeBuilder::isPrimitive(struct drgn_type* type) {

From 6a26f9ae8ed39713f1a31ccf74dc90c41c0deaff Mon Sep 17 00:00:00 2001
From: Thierry Treyer <ttreyer@fb.com>
Date: Wed, 10 Jan 2024 08:49:39 -0800
Subject: [PATCH 3/3] Enable test arrays_member_int0

---
 test/integration/arrays.toml | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/test/integration/arrays.toml b/test/integration/arrays.toml
index 5074b624..25e542a4 100644
--- a/test/integration/arrays.toml
+++ b/test/integration/arrays.toml
@@ -42,10 +42,6 @@ definitions = '''
         "capacity":10
       }]}]'''
   [cases.member_int0]
-    oil_skip = 'zero length arrays fail codegen v2' # https://github.com/facebookexperimental/object-introspection/issues/295
-    # WARNING: zero-length arrays are handled differently to non-empty arrays.
-    # They end up not being treated as containers. This should probably change
-    # in the future.
     param_types = ["const Foo0&"]
     setup = "return {};"
     expect_json = '''[{
@@ -56,13 +52,13 @@ definitions = '''
         "dynamicSize":0
       }]}]'''
     expect_json_v2 = '''[{
-      "staticSize":1,
-      "exclusiveSize":1,
-      "size":1,
+      "staticSize":0,
+      "exclusiveSize":0,
+      "size":0,
       "members":[{
         "staticSize":0,
         "exclusiveSize":0,
-        "size":1
+        "size":0
       }]}]'''
   [cases.multidim_legacy] # Test for legacy behaviour. Remove with OICodeGen
     oil_disable = 'oil only runs on codegen v2'