Default initialize properties in custom structs

[RSNara]

Summary:
If a native module spec declares a custom type:

https://www.internalfb.com/code/fbsource/[f6aeb413dbc3]/xplat/js/RKJSModules/Libraries/hsr/tm/code/editable_object/NativeEditableObjectModule.js?lines=151-154

The codegen will generate a c++ struct for that type, like so:

template <typename P0, typename P1>
struct NativeEditableObjectModuleChangedProperty {
  P0 propertyPath;
  P1 value;

  bool operator==(const NativeEditableObjectModuleChangedProperty &other) const {
    return propertyPath == other.propertyPath && value == other.value;
  }
};

Problem

People can sometimes forget to default initialize this struct:

• Report: post
• Diff nil #1: D74868762
• Diff pthread.h not found #2: D77182083

In this scenario, all the members contain garbage data.

Changes

This diff ensures that all the members are always default initialized, like so:

template <typename P0, typename P1>
struct NativeEditableObjectModuleChangedProperty {
  P0 propertyPath{};
  P1 value{};

  bool operator==(const NativeEditableObjectModuleChangedProperty &other) const {
    return propertyPath == other.propertyPath && value == other.value;
  }
};

This way, even if you forget to default initailize the struct, the members will still be default initialized.

Concerns/Risks

This could cause compilation issues in some of our existing native modules. (if one of the member types doesn't have a default constructor).

Code could start behaving differently, now that all the members are default initialized. (my hunch is that the risk from this causing a problem is low).

Changelog: [General][Changed] c++ tm codegen: Default initialize properties in custom structs

Reviewed By: christophpurrer

Differential Revision: D77315742

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D77315742

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D77315742