Implement Debug trait for Rust flatbuffers. (#6207)

* Refactor idl_gen_rust to a ForAllX continuation pattern.

* Removed unneeded SetValue and updated sample rust gencode

* Make Rust flatbuffers print right

* Generated code and removed unnecessary trait constraint

* bumped rust version. Release required

* removed an unwrap in Rust Debug-print unions

* Tested formatting flatbuffers in rust.

* Set float precision in flaky debug-print test

* impl Debug for structs too

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

samples/monster_generated.rs

@@ -173,12 +173,22 @@ impl flatbuffers::EndianScalar for Equipment {
 pub struct EquipmentUnionTableOffset {}
 // struct Vec3, aligned to 4
 #[repr(C, align(4))]
-#[derive(Clone, Copy, Debug, PartialEq)]
+#[derive(Clone, Copy, PartialEq)]
 pub struct Vec3 {
   x_: f32,
   y_: f32,
   z_: f32,
 } // pub struct Vec3
+impl std::fmt::Debug for Vec3 {
+  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+    f.debug_struct("Vec3")
+      .field("x", &self.x())
+      .field("y", &self.y())
+      .field("z", &self.z())
+      .finish()
+  }
+}
+
 impl flatbuffers::SafeSliceAccess for Vec3 {}
 impl<'a> flatbuffers::Follow<'a> for Vec3 {
   type Inner = &'a Vec3;
@@ -238,7 +248,7 @@ impl Vec3 {
 }
 
 pub enum MonsterOffset {}
-#[derive(Copy, Clone, Debug, PartialEq)]
+#[derive(Copy, Clone, PartialEq)]
 
 pub struct Monster<'a> {
   pub _tab: flatbuffers::Table<'a>,
@@ -429,8 +439,36 @@ impl<'a: 'b, 'b> MonsterBuilder<'a, 'b> {
   }
 }
 
+impl std::fmt::Debug for Monster<'_> {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    let mut ds = f.debug_struct("Monster");
+      ds.field("pos", &self.pos());
+      ds.field("mana", &self.mana());
+      ds.field("hp", &self.hp());
+      ds.field("name", &self.name());
+      ds.field("inventory", &self.inventory());
+      ds.field("color", &self.color());
+      ds.field("weapons", &self.weapons());
+      ds.field("equipped_type", &self.equipped_type());
+      match self.equipped_type() {
+        Equipment::Weapon => {
+          if let Some(x) = self.equipped_as_weapon() {
+            ds.field("equipped", &x)
+          } else {
+            ds.field("equipped", &"InvalidFlatbuffer: Union discriminant does not match value.")
+          }
+        },
+        _ => { 
+          let x: Option<()> = None;
+          ds.field("equipped", &x)
+        },
+      };
+      ds.field("path", &self.path());
+      ds.finish()
+  }
+}
 pub enum WeaponOffset {}
-#[derive(Copy, Clone, Debug, PartialEq)]
+#[derive(Copy, Clone, PartialEq)]
 
 pub struct Weapon<'a> {
   pub _tab: flatbuffers::Table<'a>,
@@ -515,6 +553,14 @@ impl<'a: 'b, 'b> WeaponBuilder<'a, 'b> {
   }
 }
 
+impl std::fmt::Debug for Weapon<'_> {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    let mut ds = f.debug_struct("Weapon");
+      ds.field("name", &self.name());
+      ds.field("damage", &self.damage());
+      ds.finish()
+  }
+}
 #[inline]
 pub fn get_root_as_monster<'a>(buf: &'a [u8]) -> Monster<'a> {
   flatbuffers::get_root::<Monster<'a>>(buf)

samples/sample_binary.rs

@@ -152,6 +152,7 @@ fn main() {
   //assert_eq!(monster.path().unwrap()[1].x(), 4.0);
 
   println!("The FlatBuffer was successfully created and accessed!");
+  dbg!(monster);
 }
 
 #[cfg(test)]