[Rust] Ensure unions are referenced with the correct path (#6422)

* Add codegen test for namespaced unions

* [Rust] Handle cross-namespace union use

* [Rust] Test namespace handling

* [Rust] Drop trailing whitespace in codegen

* [Rust] Set flags in generate_code.bat to match .sh

* [C#] Add additional namespace test file

tests/namespace_test/namespace_test1_generated.rs

@@ -26,6 +26,138 @@ pub mod namespace_b {
   extern crate flatbuffers;
   use self::flatbuffers::EndianScalar;
 
+#[deprecated(since = "2.0.0", note = "Use associated constants instead. This will no longer be generated in 2021.")]
+pub const ENUM_MIN_UNION_IN_NESTED_NS: u8 = 0;
+#[deprecated(since = "2.0.0", note = "Use associated constants instead. This will no longer be generated in 2021.")]
+pub const ENUM_MAX_UNION_IN_NESTED_NS: u8 = 1;
+#[deprecated(since = "2.0.0", note = "Use associated constants instead. This will no longer be generated in 2021.")]
+#[allow(non_camel_case_types)]
+pub const ENUM_VALUES_UNION_IN_NESTED_NS: [UnionInNestedNS; 2] = [
+  UnionInNestedNS::NONE,
+  UnionInNestedNS::TableInNestedNS,
+];
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
+#[repr(transparent)]
+pub struct UnionInNestedNS(pub u8);
+#[allow(non_upper_case_globals)]
+impl UnionInNestedNS {
+  pub const NONE: Self = Self(0);
+  pub const TableInNestedNS: Self = Self(1);
+
+  pub const ENUM_MIN: u8 = 0;
+  pub const ENUM_MAX: u8 = 1;
+  pub const ENUM_VALUES: &'static [Self] = &[
+    Self::NONE,
+    Self::TableInNestedNS,
+  ];
+  /// Returns the variant's name or "" if unknown.
+  pub fn variant_name(self) -> Option<&'static str> {
+    match self {
+      Self::NONE => Some("NONE"),
+      Self::TableInNestedNS => Some("TableInNestedNS"),
+      _ => None,
+    }
+  }
+}
+impl std::fmt::Debug for UnionInNestedNS {
+  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+    if let Some(name) = self.variant_name() {
+      f.write_str(name)
+    } else {
+      f.write_fmt(format_args!("<UNKNOWN {:?}>", self.0))
+    }
+  }
+}
+impl<'a> flatbuffers::Follow<'a> for UnionInNestedNS {
+  type Inner = Self;
+  #[inline]
+  fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
+    let b = flatbuffers::read_scalar_at::<u8>(buf, loc);
+    Self(b)
+  }
+}
+
+impl flatbuffers::Push for UnionInNestedNS {
+    type Output = UnionInNestedNS;
+    #[inline]
+    fn push(&self, dst: &mut [u8], _rest: &[u8]) {
+        flatbuffers::emplace_scalar::<u8>(dst, self.0);
+    }
+}
+
+impl flatbuffers::EndianScalar for UnionInNestedNS {
+  #[inline]
+  fn to_little_endian(self) -> Self {
+    let b = u8::to_le(self.0);
+    Self(b)
+  }
+  #[inline]
+  fn from_little_endian(self) -> Self {
+    let b = u8::from_le(self.0);
+    Self(b)
+  }
+}
+
+impl<'a> flatbuffers::Verifiable for UnionInNestedNS {
+  #[inline]
+  fn run_verifier(
+    v: &mut flatbuffers::Verifier, pos: usize
+  ) -> Result<(), flatbuffers::InvalidFlatbuffer> {
+    use self::flatbuffers::Verifiable;
+    u8::run_verifier(v, pos)
+  }
+}
+
+impl flatbuffers::SimpleToVerifyInSlice for UnionInNestedNS {}
+pub struct UnionInNestedNSUnionTableOffset {}
+
+#[non_exhaustive]
+#[derive(Debug, Clone, PartialEq)]
+pub enum UnionInNestedNST {
+  NONE,
+  TableInNestedNS(Box<TableInNestedNST>),
+}
+impl Default for UnionInNestedNST {
+  fn default() -> Self {
+    Self::NONE
+  }
+}
+impl UnionInNestedNST {
+  pub fn union_in_nested_ns_type(&self) -> UnionInNestedNS {
+    match self {
+      Self::NONE => UnionInNestedNS::NONE,
+      Self::TableInNestedNS(_) => UnionInNestedNS::TableInNestedNS,
+    }
+  }
+  pub fn pack(&self, fbb: &mut flatbuffers::FlatBufferBuilder) -> Option<flatbuffers::WIPOffset<flatbuffers::UnionWIPOffset>> {
+    match self {
+      Self::NONE => None,
+      Self::TableInNestedNS(v) => Some(v.pack(fbb).as_union_value()),
+    }
+  }
+  /// If the union variant matches, return the owned TableInNestedNST, setting the union to NONE.
+  pub fn take_table_in_nested_ns(&mut self) -> Option<Box<TableInNestedNST>> {
+    if let Self::TableInNestedNS(_) = self {
+      let v = std::mem::replace(self, Self::NONE);
+      if let Self::TableInNestedNS(w) = v {
+        Some(w)
+      } else {
+        unreachable!()
+      }
+    } else {
+      None
+    }
+  }
+  /// If the union variant matches, return a reference to the TableInNestedNST.
+  pub fn as_table_in_nested_ns(&self) -> Option<&TableInNestedNST> {
+    if let Self::TableInNestedNS(v) = self { Some(v.as_ref()) } else { None }
+  }
+  /// If the union variant matches, return a mutable reference to the TableInNestedNST.
+  pub fn as_table_in_nested_ns_mut(&mut self) -> Option<&mut TableInNestedNST> {
+    if let Self::TableInNestedNS(v) = self { Some(v.as_mut()) } else { None }
+  }
+}
 #[deprecated(since = "2.0.0", note = "Use associated constants instead. This will no longer be generated in 2021.")]
 pub const ENUM_MIN_ENUM_IN_NESTED_NS: i8 = 0;
 #[deprecated(since = "2.0.0", note = "Use associated constants instead. This will no longer be generated in 2021.")]