ARROW-11222: [Rust] Catch up with flatbuffers 0.8.1 which had some UB…

… problems fixed

The major change of [flatbuffers 0.8.1](https://docs.rs/flatbuffers/0.8.1/flatbuffers/index.html) since 0.8.0 is google/flatbuffers#6393, which fixed some possible memory alignment issues.

In this PR, the ipc/gen/*.rs files are generated by `regen.sh` as before, without any manual change.

Closes apache#9176 from mqy/flatbuffers-0.8.1

Authored-by: mqy <meng.qingyou@gmail.com>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>

rust/arrow/regen.sh

@@ -21,13 +21,11 @@ DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
 # Change to the toplevel Rust directory
 pushd $DIR/../../
 
-# As of 2020-12-06, the snapshot flatc version is not changed since "1.12.0",
-# so let's build flatc from source.
-
 echo "Build flatc from source ..."
 
 FB_URL="https://github.com/google/flatbuffers"
-FB_COMMIT="05192553f434d10c5f585aeb6a07a55a6ac702a5"
+# https://github.com/google/flatbuffers/pull/6393
+FB_COMMIT="408cf5802415e1dea65fef7489a6c2f3740fb381"
 FB_DIR="rust/arrow/.flatbuffers"
 FLATC="$FB_DIR/bazel-bin/flatc"
 

rust/arrow/src/ipc/gen/File.rs

@@ -24,14 +24,9 @@ use std::{cmp::Ordering, mem};
 // automatically generated by the FlatBuffers compiler, do not modify
 
 // struct Block, aligned to 8
-#[repr(C, align(8))]
+#[repr(transparent)]
 #[derive(Clone, Copy, PartialEq)]
-pub struct Block {
-    offset_: i64,
-    metaDataLength_: i32,
-    padding0__: u32,
-    bodyLength_: i64,
-} // pub struct Block
+pub struct Block(pub [u8; 24]);
 impl std::fmt::Debug for Block {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         f.debug_struct("Block")
@@ -82,36 +77,98 @@ impl<'b> flatbuffers::Push for &'b Block {
 
 impl<'a> flatbuffers::Verifiable for Block {
     #[inline]
-    fn run_verifier<'o, 'b>(
-        v: &mut flatbuffers::Verifier<'o, 'b>,
+    fn run_verifier(
+        v: &mut flatbuffers::Verifier,
         pos: usize,
     ) -> Result<(), flatbuffers::InvalidFlatbuffer> {
         use flatbuffers::Verifiable;
         v.in_buffer::<Self>(pos)
     }
 }
 impl Block {
-    pub fn new(_offset: i64, _metaDataLength: i32, _bodyLength: i64) -> Self {
-        Block {
-            offset_: _offset.to_little_endian(),
-            metaDataLength_: _metaDataLength.to_little_endian(),
-            bodyLength_: _bodyLength.to_little_endian(),
-
-            padding0__: 0,
-        }
+    #[allow(clippy::too_many_arguments)]
+    pub fn new(offset: i64, metaDataLength: i32, bodyLength: i64) -> Self {
+        let mut s = Self([0; 24]);
+        s.set_offset(offset);
+        s.set_metaDataLength(metaDataLength);
+        s.set_bodyLength(bodyLength);
+        s
     }
+
     /// Index to the start of the RecordBlock (note this is past the Message header)
     pub fn offset(&self) -> i64 {
-        self.offset_.from_little_endian()
+        let mut mem = core::mem::MaybeUninit::<i64>::uninit();
+        unsafe {
+            core::ptr::copy_nonoverlapping(
+                self.0[0..].as_ptr(),
+                mem.as_mut_ptr() as *mut u8,
+                core::mem::size_of::<i64>(),
+            );
+            mem.assume_init()
+        }
+        .from_little_endian()
+    }
+
+    pub fn set_offset(&mut self, x: i64) {
+        let x_le = x.to_little_endian();
+        unsafe {
+            core::ptr::copy_nonoverlapping(
+                &x_le as *const i64 as *const u8,
+                self.0[0..].as_mut_ptr(),
+                core::mem::size_of::<i64>(),
+            );
+        }
     }
+
     /// Length of the metadata
     pub fn metaDataLength(&self) -> i32 {
-        self.metaDataLength_.from_little_endian()
+        let mut mem = core::mem::MaybeUninit::<i32>::uninit();
+        unsafe {
+            core::ptr::copy_nonoverlapping(
+                self.0[8..].as_ptr(),
+                mem.as_mut_ptr() as *mut u8,
+                core::mem::size_of::<i32>(),
+            );
+            mem.assume_init()
+        }
+        .from_little_endian()
     }
+
+    pub fn set_metaDataLength(&mut self, x: i32) {
+        let x_le = x.to_little_endian();
+        unsafe {
+            core::ptr::copy_nonoverlapping(
+                &x_le as *const i32 as *const u8,
+                self.0[8..].as_mut_ptr(),
+                core::mem::size_of::<i32>(),
+            );
+        }
+    }
+
     /// Length of the data (this is aligned so there can be a gap between this and
     /// the metadata).
     pub fn bodyLength(&self) -> i64 {
-        self.bodyLength_.from_little_endian()
+        let mut mem = core::mem::MaybeUninit::<i64>::uninit();
+        unsafe {
+            core::ptr::copy_nonoverlapping(
+                self.0[16..].as_ptr(),
+                mem.as_mut_ptr() as *mut u8,
+                core::mem::size_of::<i64>(),
+            );
+            mem.assume_init()
+        }
+        .from_little_endian()
+    }
+
+    pub fn set_bodyLength(&mut self, x: i64) {
+        let x_le = x.to_little_endian();
+        unsafe {
+            core::ptr::copy_nonoverlapping(
+                &x_le as *const i64 as *const u8,
+                self.0[16..].as_mut_ptr(),
+                core::mem::size_of::<i64>(),
+            );
+        }
     }
 }
 
@@ -210,8 +267,8 @@ impl<'a> Footer<'a> {
 
 impl flatbuffers::Verifiable for Footer<'_> {
     #[inline]
-    fn run_verifier<'o, 'b>(
-        v: &mut flatbuffers::Verifier<'o, 'b>,
+    fn run_verifier(
+        v: &mut flatbuffers::Verifier,
         pos: usize,
     ) -> Result<(), flatbuffers::InvalidFlatbuffer> {
         use flatbuffers::Verifiable;
@@ -344,13 +401,13 @@ impl std::fmt::Debug for Footer<'_> {
     }
 }
 #[inline]
-#[deprecated(since = "1.13", note = "Deprecated in favor of `root_as...` methods.")]
+#[deprecated(since = "2.0.0", note = "Deprecated in favor of `root_as...` methods.")]
 pub fn get_root_as_footer<'a>(buf: &'a [u8]) -> Footer<'a> {
     unsafe { flatbuffers::root_unchecked::<Footer<'a>>(buf) }
 }
 
 #[inline]
-#[deprecated(since = "1.13", note = "Deprecated in favor of `root_as...` methods.")]
+#[deprecated(since = "2.0.0", note = "Deprecated in favor of `root_as...` methods.")]
 pub fn get_size_prefixed_root_as_footer<'a>(buf: &'a [u8]) -> Footer<'a> {
     unsafe { flatbuffers::size_prefixed_root_unchecked::<Footer<'a>>(buf) }
 }