From fa232ac544f89e33e04bc8477d9f0a63a7eb4038 Mon Sep 17 00:00:00 2001
From: Jack Chistyakov <jchistyakov@meta.com>
Date: Wed, 17 May 2023 12:34:15 -0700
Subject: [PATCH] Legacy/compat setter for containers

Summary: Support container (map/list/set) setters in legacy/compat mode - for complete forwards/backwards compatibility with the legacy Go generator.

Reviewed By: leoleovich

Differential Revision: D45838418

fbshipit-source-id: 495b1928682da8f5d66c3d75137225a3e2987841
---
 .../compiler/generate/t_mstch_go_generator.cc | 41 ++++++++++++++-----
 .../go/types/field_method_set.mustache        | 10 ++++-
 2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/third-party/thrift/src/thrift/compiler/generate/t_mstch_go_generator.cc b/third-party/thrift/src/thrift/compiler/generate/t_mstch_go_generator.cc
index 07bf89ae2a3d80..a5c431c475ee11 100644
--- a/third-party/thrift/src/thrift/compiler/generate/t_mstch_go_generator.cc
+++ b/third-party/thrift/src/thrift/compiler/generate/t_mstch_go_generator.cc
@@ -322,6 +322,8 @@ class mstch_go_field : public mstch_field {
             {"field:pointer?", &mstch_go_field::is_pointer},
             {"field:compat_setter_pointer?",
              &mstch_go_field::is_compat_setter_pointer},
+            {"field:compat_setter_value_op",
+             &mstch_go_field::compat_setter_value_op},
             {"field:nilable?", &mstch_go_field::is_nilable},
             {"field:dereference?", &mstch_go_field::should_dereference},
             {"field:key_str", &mstch_go_field::key_str},
@@ -372,17 +374,17 @@ class mstch_go_field : public mstch_field {
     auto real_type = field_->type()->get_true_type();
     return is_pointer_() && !go::is_type_go_struct(real_type);
   }
-  mstch::node is_compat_setter_pointer() {
-    // Whether this field's value should be a poitner in compat-setter.
-    // This is needed for a seamless migration from the legacy generator.
-    //
-    // Legacy generator would make optional fields with default values be
-    // impelemented as non-pointer fields. This is incorrect because such
-    // field cannot be unset (i.e set to nil) despite being optional.
-    // This ommision is fixed in the new generator, however, our compat
-    // setters must be backwards compatible to ensure graceful migration.
-    bool has_default_value = (field_->default_value() != nullptr);
-    return is_pointer_() && !(is_optional_() && has_default_value);
+  mstch::node is_compat_setter_pointer() { return is_compat_setter_pointer_(); }
+  mstch::node compat_setter_value_op() {
+    if (is_pointer_() && is_compat_setter_pointer_()) {
+      return std::string("");
+    } else if (is_pointer_() && !is_compat_setter_pointer_()) {
+      return std::string("&");
+    } else if (!is_pointer_() && !is_compat_setter_pointer_()) {
+      return std::string("");
+    } else { // if (!is_pointer_() && is_compat_setter_pointer_())
+      return std::string("*");
+    }
   }
   mstch::node key_str() {
     // Legacy schemas may have negative tags - replace minus with an underscore.
@@ -423,6 +425,23 @@ class mstch_go_field : public mstch_field {
         !go::is_type_nilable(real_type);
   }
 
+  bool is_compat_setter_pointer_() {
+    // Whether this field's value should be a pointer in compat-setter.
+    // This is needed for a seamless migration from the legacy generator.
+    //
+    // Legacy generator treats optional fields with default values differently
+    // compared to the new generator (pointer vs non-pointer).
+    // This method helps with backwards compatibility.
+    bool has_default_value = (field_->default_value() != nullptr);
+    if (is_optional_() && has_default_value) {
+      auto real_type = field_->type()->get_true_type();
+      bool is_container =
+          (real_type->is_list() || real_type->is_map() || real_type->is_set());
+      return is_container;
+    }
+    return is_pointer_();
+  }
+
   bool is_inside_union_() {
     // Whether field is part of a union
     return field_context_ != nullptr && field_context_->strct != nullptr &&
diff --git a/third-party/thrift/src/thrift/compiler/generate/templates/go/types/field_method_set.mustache b/third-party/thrift/src/thrift/compiler/generate/templates/go/types/field_method_set.mustache
index 18e03cf738c895..5373e250ad37c6 100644
--- a/third-party/thrift/src/thrift/compiler/generate/templates/go/types/field_method_set.mustache
+++ b/third-party/thrift/src/thrift/compiler/generate/templates/go/types/field_method_set.mustache
@@ -26,7 +26,15 @@ func (x *{{struct:go_name}}) {{field:go_setter_name}}{{#program:compat_setters?}
 {{#program:compat_setters?}}
 
 func (x *{{struct:go_name}}) {{field:go_setter_name}}(value {{#field:compat_setter_pointer?}}*{{/field:compat_setter_pointer?}}{{#field:type}}{{> common/type}}{{/field:type}}) *{{struct:go_name}} {
-    x.{{field:go_name}} = {{^field:compat_setter_pointer?}}{{#field:pointer?}}&{{/field:pointer?}}{{/field:compat_setter_pointer?}}value
+    {{#field:compat_setter_pointer?}}
+    {{^field:pointer?}}
+    if (value == nil) {
+        x.{{field:go_name}} = nil
+        return x
+    }
+    {{/field:pointer?}}
+    {{/field:compat_setter_pointer?}}
+    x.{{field:go_name}} = {{field:compat_setter_value_op}}value
     return x
 }
 {{/program:compat_setters?}}