Make flatc generate Rust files not requiring std (#7273)

* Set an explicit 2018 edition for Rust tests

* Replace all `std` usage with `core` and `alloc` in Rust code generator

* Update the generated files

* Make Rust tests actually use no_std when the corresponding feature is enabled

tests/monster_test_serialize/my_game/example/ability_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -15,8 +19,8 @@ impl Default for Ability {
     Self([0; 8])
   }
 }
-impl std::fmt::Debug for Ability {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for Ability {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     f.debug_struct("Ability")
       .field("id", &self.id())
       .field("distance", &self.distance())
@@ -45,7 +49,7 @@ impl<'b> flatbuffers::Push for Ability {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(self as *const Ability as *const u8, Self::size())
+            ::core::slice::from_raw_parts(self as *const Ability as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -56,7 +60,7 @@ impl<'b> flatbuffers::Push for &'b Ability {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(*self as *const Ability as *const u8, Self::size())
+            ::core::slice::from_raw_parts(*self as *const Ability as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -129,7 +133,7 @@ impl<'a> Ability {
   }
 
   #[inline]
-  pub fn key_compare_with_value(&self, val: u32) -> ::std::cmp::Ordering {
+  pub fn key_compare_with_value(&self, val: u32) -> ::core::cmp::Ordering {
     let key = self.id();
     key.cmp(&val)
   }

tests/monster_test_serialize/my_game/example/any_ambiguous_aliases_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -48,8 +52,8 @@ impl AnyAmbiguousAliases {
     }
   }
 }
-impl std::fmt::Debug for AnyAmbiguousAliases {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for AnyAmbiguousAliases {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     if let Some(name) = self.variant_name() {
       f.write_str(name)
     } else {
@@ -146,7 +150,7 @@ impl AnyAmbiguousAliasesT {
   /// If the union variant matches, return the owned MonsterT, setting the union to NONE.
   pub fn take_m1(&mut self) -> Option<Box<MonsterT>> {
     if let Self::M1(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::M1(w) = v {
         Some(w)
       } else {
@@ -167,7 +171,7 @@ impl AnyAmbiguousAliasesT {
   /// If the union variant matches, return the owned MonsterT, setting the union to NONE.
   pub fn take_m2(&mut self) -> Option<Box<MonsterT>> {
     if let Self::M2(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::M2(w) = v {
         Some(w)
       } else {
@@ -188,7 +192,7 @@ impl AnyAmbiguousAliasesT {
   /// If the union variant matches, return the owned MonsterT, setting the union to NONE.
   pub fn take_m3(&mut self) -> Option<Box<MonsterT>> {
     if let Self::M3(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::M3(w) = v {
         Some(w)
       } else {

tests/monster_test_serialize/my_game/example/any_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -48,8 +52,8 @@ impl Any {
     }
   }
 }
-impl std::fmt::Debug for Any {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for Any {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     if let Some(name) = self.variant_name() {
       f.write_str(name)
     } else {
@@ -146,7 +150,7 @@ impl AnyT {
   /// If the union variant matches, return the owned MonsterT, setting the union to NONE.
   pub fn take_monster(&mut self) -> Option<Box<MonsterT>> {
     if let Self::Monster(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::Monster(w) = v {
         Some(w)
       } else {
@@ -167,7 +171,7 @@ impl AnyT {
   /// If the union variant matches, return the owned TestSimpleTableWithEnumT, setting the union to NONE.
   pub fn take_test_simple_table_with_enum(&mut self) -> Option<Box<TestSimpleTableWithEnumT>> {
     if let Self::TestSimpleTableWithEnum(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::TestSimpleTableWithEnum(w) = v {
         Some(w)
       } else {
@@ -188,7 +192,7 @@ impl AnyT {
   /// If the union variant matches, return the owned super::example_2::MonsterT, setting the union to NONE.
   pub fn take_my_game_example_2_monster(&mut self) -> Option<Box<super::example_2::MonsterT>> {
     if let Self::MyGameExample2Monster(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::MyGameExample2Monster(w) = v {
         Some(w)
       } else {

tests/monster_test_serialize/my_game/example/any_unique_aliases_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -48,8 +52,8 @@ impl AnyUniqueAliases {
     }
   }
 }
-impl std::fmt::Debug for AnyUniqueAliases {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for AnyUniqueAliases {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     if let Some(name) = self.variant_name() {
       f.write_str(name)
     } else {
@@ -146,7 +150,7 @@ impl AnyUniqueAliasesT {
   /// If the union variant matches, return the owned MonsterT, setting the union to NONE.
   pub fn take_m(&mut self) -> Option<Box<MonsterT>> {
     if let Self::M(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::M(w) = v {
         Some(w)
       } else {
@@ -167,7 +171,7 @@ impl AnyUniqueAliasesT {
   /// If the union variant matches, return the owned TestSimpleTableWithEnumT, setting the union to NONE.
   pub fn take_ts(&mut self) -> Option<Box<TestSimpleTableWithEnumT>> {
     if let Self::TS(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::TS(w) = v {
         Some(w)
       } else {
@@ -188,7 +192,7 @@ impl AnyUniqueAliasesT {
   /// If the union variant matches, return the owned super::example_2::MonsterT, setting the union to NONE.
   pub fn take_m2(&mut self) -> Option<Box<super::example_2::MonsterT>> {
     if let Self::M2(_) = self {
-      let v = std::mem::replace(self, Self::NONE);
+      let v = core::mem::replace(self, Self::NONE);
       if let Self::M2(w) = v {
         Some(w)
       } else {

tests/monster_test_serialize/my_game/example/color_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};

tests/monster_test_serialize/my_game/example/long_enum_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};

tests/monster_test_serialize/my_game/example/monster_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -381,7 +385,7 @@ impl<'a> Monster<'a> {
   }
 
   #[inline]
-  pub fn key_compare_with_value(&self, val: & str) -> ::std::cmp::Ordering {
+  pub fn key_compare_with_value(&self, val: & str) -> ::core::cmp::Ordering {
     let key = self.name();
     key.cmp(val)
   }
@@ -1335,8 +1339,8 @@ impl<'a: 'b, 'b> MonsterBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for Monster<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for Monster<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("Monster");
       ds.field("pos", &self.pos());
       ds.field("mana", &self.mana());

tests/monster_test_serialize/my_game/example/race_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -48,8 +52,8 @@ impl Race {
     }
   }
 }
-impl std::fmt::Debug for Race {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for Race {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     if let Some(name) = self.variant_name() {
       f.write_str(name)
     } else {

tests/monster_test_serialize/my_game/example/referrable_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -59,7 +63,7 @@ impl<'a> Referrable<'a> {
   }
 
   #[inline]
-  pub fn key_compare_with_value(&self, val: u64) -> ::std::cmp::Ordering {
+  pub fn key_compare_with_value(&self, val: u64) -> ::core::cmp::Ordering {
     let key = self.id();
     key.cmp(&val)
   }
@@ -124,8 +128,8 @@ impl<'a: 'b, 'b> ReferrableBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for Referrable<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for Referrable<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("Referrable");
       ds.field("id", &self.id());
       ds.finish()

tests/monster_test_serialize/my_game/example/stat_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -77,7 +81,7 @@ impl<'a> Stat<'a> {
   }
 
   #[inline]
-  pub fn key_compare_with_value(&self, val: u16) -> ::std::cmp::Ordering {
+  pub fn key_compare_with_value(&self, val: u16) -> ::core::cmp::Ordering {
     let key = self.count();
     key.cmp(&val)
   }
@@ -162,8 +166,8 @@ impl<'a: 'b, 'b> StatBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for Stat<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for Stat<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("Stat");
       ds.field("id", &self.id());
       ds.field("val", &self.val());

tests/monster_test_serialize/my_game/example/struct_of_structs_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -15,8 +19,8 @@ impl Default for StructOfStructs {
     Self([0; 20])
   }
 }
-impl std::fmt::Debug for StructOfStructs {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for StructOfStructs {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     f.debug_struct("StructOfStructs")
       .field("a", &self.a())
       .field("b", &self.b())
@@ -46,7 +50,7 @@ impl<'b> flatbuffers::Push for StructOfStructs {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(self as *const StructOfStructs as *const u8, Self::size())
+            ::core::slice::from_raw_parts(self as *const StructOfStructs as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -57,7 +61,7 @@ impl<'b> flatbuffers::Push for &'b StructOfStructs {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(*self as *const StructOfStructs as *const u8, Self::size())
+            ::core::slice::from_raw_parts(*self as *const StructOfStructs as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }

tests/monster_test_serialize/my_game/example/struct_of_structs_of_structs_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -15,8 +19,8 @@ impl Default for StructOfStructsOfStructs {
     Self([0; 20])
   }
 }
-impl std::fmt::Debug for StructOfStructsOfStructs {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for StructOfStructsOfStructs {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     f.debug_struct("StructOfStructsOfStructs")
       .field("a", &self.a())
       .finish()
@@ -44,7 +48,7 @@ impl<'b> flatbuffers::Push for StructOfStructsOfStructs {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(self as *const StructOfStructsOfStructs as *const u8, Self::size())
+            ::core::slice::from_raw_parts(self as *const StructOfStructsOfStructs as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -55,7 +59,7 @@ impl<'b> flatbuffers::Push for &'b StructOfStructsOfStructs {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(*self as *const StructOfStructsOfStructs as *const u8, Self::size())
+            ::core::slice::from_raw_parts(*self as *const StructOfStructsOfStructs as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }

tests/monster_test_serialize/my_game/example/test_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -15,8 +19,8 @@ impl Default for Test {
     Self([0; 4])
   }
 }
-impl std::fmt::Debug for Test {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for Test {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     f.debug_struct("Test")
       .field("a", &self.a())
       .field("b", &self.b())
@@ -45,7 +49,7 @@ impl<'b> flatbuffers::Push for Test {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(self as *const Test as *const u8, Self::size())
+            ::core::slice::from_raw_parts(self as *const Test as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -56,7 +60,7 @@ impl<'b> flatbuffers::Push for &'b Test {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(*self as *const Test as *const u8, Self::size())
+            ::core::slice::from_raw_parts(*self as *const Test as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }

tests/monster_test_serialize/my_game/example/test_simple_table_with_enum_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -114,8 +118,8 @@ impl<'a: 'b, 'b> TestSimpleTableWithEnumBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for TestSimpleTableWithEnum<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for TestSimpleTableWithEnum<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("TestSimpleTableWithEnum");
       ds.field("color", &self.color());
       ds.finish()

tests/monster_test_serialize/my_game/example/type_aliases_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -302,8 +306,8 @@ impl<'a: 'b, 'b> TypeAliasesBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for TypeAliases<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for TypeAliases<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("TypeAliases");
       ds.field("i8_", &self.i8_());
       ds.field("u8_", &self.u8_());

tests/monster_test_serialize/my_game/example/vec_3_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -15,8 +19,8 @@ impl Default for Vec3 {
     Self([0; 32])
   }
 }
-impl std::fmt::Debug for Vec3 {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for Vec3 {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     f.debug_struct("Vec3")
       .field("x", &self.x())
       .field("y", &self.y())
@@ -49,7 +53,7 @@ impl<'b> flatbuffers::Push for Vec3 {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(self as *const Vec3 as *const u8, Self::size())
+            ::core::slice::from_raw_parts(self as *const Vec3 as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -60,7 +64,7 @@ impl<'b> flatbuffers::Push for &'b Vec3 {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(*self as *const Vec3 as *const u8, Self::size())
+            ::core::slice::from_raw_parts(*self as *const Vec3 as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }

tests/monster_test_serialize/my_game/example_2/monster_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -97,8 +101,8 @@ impl<'a: 'b, 'b> MonsterBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for Monster<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for Monster<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("Monster");
       ds.finish()
   }

tests/monster_test_serialize/my_game/in_parent_namespace_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -97,8 +101,8 @@ impl<'a: 'b, 'b> InParentNamespaceBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for InParentNamespace<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for InParentNamespace<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("InParentNamespace");
       ds.finish()
   }

tests/monster_test_serialize/my_game/other_name_space/from_include_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -36,8 +40,8 @@ impl FromInclude {
     }
   }
 }
-impl std::fmt::Debug for FromInclude {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for FromInclude {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     if let Some(name) = self.variant_name() {
       f.write_str(name)
     } else {

tests/monster_test_serialize/my_game/other_name_space/table_b_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -120,8 +124,8 @@ impl<'a: 'b, 'b> TableBBuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for TableB<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for TableB<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("TableB");
       ds.field("a", &self.a());
       ds.finish()

tests/monster_test_serialize/my_game/other_name_space/unused_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -15,8 +19,8 @@ impl Default for Unused {
     Self([0; 4])
   }
 }
-impl std::fmt::Debug for Unused {
-  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Debug for Unused {
+  fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
     f.debug_struct("Unused")
       .field("a", &self.a())
       .finish()
@@ -44,7 +48,7 @@ impl<'b> flatbuffers::Push for Unused {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(self as *const Unused as *const u8, Self::size())
+            ::core::slice::from_raw_parts(self as *const Unused as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }
@@ -55,7 +59,7 @@ impl<'b> flatbuffers::Push for &'b Unused {
     #[inline]
     fn push(&self, dst: &mut [u8], _rest: &[u8]) {
         let src = unsafe {
-            ::std::slice::from_raw_parts(*self as *const Unused as *const u8, Self::size())
+            ::core::slice::from_raw_parts(*self as *const Unused as *const u8, Self::size())
         };
         dst.copy_from_slice(src);
     }

tests/monster_test_serialize/table_a_generated.rs

@@ -1,7 +1,11 @@
 // automatically generated by the FlatBuffers compiler, do not modify
+extern crate alloc;
 extern crate flatbuffers;
-use std::mem;
-use std::cmp::Ordering;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::mem;
+use core::cmp::Ordering;
 extern crate serde;
 use self::serde::ser::{Serialize, Serializer, SerializeStruct};
 use self::flatbuffers::{EndianScalar, Follow};
@@ -120,8 +124,8 @@ impl<'a: 'b, 'b> TableABuilder<'a, 'b> {
   }
 }
 
-impl std::fmt::Debug for TableA<'_> {
-  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl core::fmt::Debug for TableA<'_> {
+  fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
     let mut ds = f.debug_struct("TableA");
       ds.field("b", &self.b());
       ds.finish()