Fix Rust UB problems (#6393)

* Fix miri problems by assuming alignment is 1 in rust

* Removed is_aligned fn from rust verifier.

* Add back is_aligned, but make it w.r.t. buffer[0]

* touch unused variable

* touch unused variable

* +nightly

* Move Rust miri testing into its own docker

* fix bash

* missing one endian conversion

* fix endianness2

* format stuff

Co-authored-by: Casper Neo <cneo@google.com>

samples/monster_generated.rs

@@ -200,13 +200,9 @@ impl<'a> flatbuffers::Verifiable for Equipment {
 
 impl flatbuffers::SimpleToVerifyInSlice for Equipment {}
 // struct Vec3, aligned to 4
-#[repr(C, align(4))]
+#[repr(transparent)]
 #[derive(Clone, Copy, PartialEq)]
-pub struct Vec3 {
-  x_: f32,
-  y_: f32,
-  z_: f32,
-} // pub struct Vec3
+pub struct Vec3(pub [u8; 12]);
 impl std::fmt::Debug for Vec3 {
   fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
     f.debug_struct("Vec3")
@@ -266,23 +262,87 @@ impl<'a> flatbuffers::Verifiable for Vec3 {
 }
 impl Vec3 {
   #[allow(clippy::too_many_arguments)]
-  pub fn new(_x: f32, _y: f32, _z: f32) -> Self {
-    Vec3 {
-      x_: _x.to_little_endian(),
-      y_: _y.to_little_endian(),
-      z_: _z.to_little_endian(),
+  pub fn new(
+    x: f32,
+    y: f32,
+    z: f32,
+  ) -> Self {
+    let mut s = Self([0; 12]);
+    s.set_x(x);
+    s.set_y(y);
+    s.set_z(z);
+    s
+  }
 
+  pub fn x(&self) -> f32 {
+    let mut mem = core::mem::MaybeUninit::<f32>::uninit();
+    unsafe {
+      core::ptr::copy_nonoverlapping(
+        self.0[0..].as_ptr(),
+        mem.as_mut_ptr() as *mut u8,
+        core::mem::size_of::<f32>(),
+      );
+      mem.assume_init()
+    }.from_little_endian()
+  }
+
+  pub fn set_x(&mut self, x: f32) {
+    let x_le = x.to_little_endian();
+    unsafe {
+      core::ptr::copy_nonoverlapping(
+        &x_le as *const f32 as *const u8,
+        self.0[0..].as_mut_ptr(),
+        core::mem::size_of::<f32>(),
+      );
     }
   }
-  pub fn x(&self) -> f32 {
-    self.x_.from_little_endian()
-  }
+
   pub fn y(&self) -> f32 {
-    self.y_.from_little_endian()
+    let mut mem = core::mem::MaybeUninit::<f32>::uninit();
+    unsafe {
+      core::ptr::copy_nonoverlapping(
+        self.0[4..].as_ptr(),
+        mem.as_mut_ptr() as *mut u8,
+        core::mem::size_of::<f32>(),
+      );
+      mem.assume_init()
+    }.from_little_endian()
   }
+
+  pub fn set_y(&mut self, x: f32) {
+    let x_le = x.to_little_endian();
+    unsafe {
+      core::ptr::copy_nonoverlapping(
+        &x_le as *const f32 as *const u8,
+        self.0[4..].as_mut_ptr(),
+        core::mem::size_of::<f32>(),
+      );
+    }
+  }
+
   pub fn z(&self) -> f32 {
-    self.z_.from_little_endian()
+    let mut mem = core::mem::MaybeUninit::<f32>::uninit();
+    unsafe {
+      core::ptr::copy_nonoverlapping(
+        self.0[8..].as_ptr(),
+        mem.as_mut_ptr() as *mut u8,
+        core::mem::size_of::<f32>(),
+      );
+      mem.assume_init()
+    }.from_little_endian()
   }
+
+  pub fn set_z(&mut self, x: f32) {
+    let x_le = x.to_little_endian();
+    unsafe {
+      core::ptr::copy_nonoverlapping(
+        &x_le as *const f32 as *const u8,
+        self.0[8..].as_mut_ptr(),
+        core::mem::size_of::<f32>(),
+      );
+    }
+  }
+
 }
 
 pub enum MonsterOffset {}