From: Matt Corallo <git@bluematt.me>
Date: Thu, 27 Jul 2023 20:00:25 +0000 (+0000)
Subject: Fix strict-aliasing violation on traits holding inner fields
X-Git-Tag: v0.0.115.3^2~2
X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=commitdiff_plain;h=cd94859a3ef20447674f393d3f169bd9e29023a1;hp=cd94859a3ef20447674f393d3f169bd9e29023a1;p=ldk-c-bindings

Fix strict-aliasing violation on traits holding inner fields

When we map a trait method which returns a reference to a struct,
we map it by storing said struct in the trait implementation
struct. Then, we create a setter method which ensures the new field
is set. Sadly, because the original Rust trait method may take a
non-mutable reference to self, we have to update the field without
a mutable reference to the trait implementation struct.

Previously we did this by simply unsafe-casting a pointer to
mutable, which violates the aliasing rules in Rust. In a recent
rustc (at least on macOS), this broke.

Here, we convert the stored struct to wrap it in an `UnsafeCell`,
which fixes the issue.
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