Please error, or at least warn, when a managed type is included in INetworkSerializeByMemcpy

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Quiet
Tech stack
csharp
Domain
networking

Research direction

Start by locating the INetworkSerializeByMemcpy definition and its validation or serialization tests. Trace how implementing types are checked during compilation or runtime, then add coverage for string and other managed fields; done means such types produce a build error or warning instead of unsafe memcpy serialization.

Written by the indexing model from the issue text.

Description

Tracking type:feature

Is your feature request related to a problem? Please describe.

My coworker was unfamiliar with INetworkSerializeByMemcpy and the FixedStringNNNBytes types, and added a string field to an existing INetworkSerializeByMemcpy struct. This caused me great headaches (it made it into a publicly released patch), trying to track down segfault heap corruption that only showed up in very specific multiplayer circumstances (the string was normally null, which probably masked the issue).

Describe the solution you'd like

Please cause a build error when a managed type (a class, a string, or the like) is included in an INetworkSerializeByMemcpy type. I cannot think of any use case where it would be valid or intended to serialize a managed GC pointer by memcpy. At least a warning if nothing else.

It doesn't have to be perfect, even just checking for string would be lovely - string specifically is such a massive footgun, it's so easy to accidentally include and think it'll work fine. The fact it crashes later on via unrelated segfault heap corruption bringing down the editor, instead of a C# Exception, is especially rough.

Dominant language
C#
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Avg merge
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Merged PRs (30d)
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