Support alloc-only no_std platforms

Author: jrobsonchase

rust/flatbuffers/Cargo.toml

@@ -11,3 +11,7 @@ categories = ["encoding", "data-structures", "memory-management"]
 
 [dependencies]
 smallvec = "0.6"
+
+[features]
+default = ["std"]
+std = []

rust/flatbuffers/src/builder.rs

@@ -16,10 +16,13 @@
 
 extern crate smallvec;
 
-use std::cmp::max;
-use std::marker::PhantomData;
-use std::ptr::write_bytes;
-use std::slice::from_raw_parts;
+#[cfg(not(feature = "std"))]
+use alloc::{vec, vec::Vec};
+
+use core::cmp::max;
+use core::marker::PhantomData;
+use core::ptr::write_bytes;
+use core::slice::from_raw_parts;
 
 use endian_scalar::{read_scalar, emplace_scalar};
 use primitives::*;
@@ -605,7 +608,7 @@ impl<'fbb> FlatBufferBuilder<'fbb> {
     fn assert_nested(&self, fn_name: &'static str) {
         // we don't assert that self.field_locs.len() >0 because the vtable
         // could be empty (e.g. for empty tables, or for all-default values).
-        debug_assert!(self.nested, format!("incorrect FlatBufferBuilder usage: {} must be called while in a nested state", fn_name));
+        debug_assert!(self.nested, "incorrect FlatBufferBuilder usage: {} must be called while in a nested state", fn_name);
     }
     #[inline]
     fn assert_not_nested(&self, msg: &'static str) {

rust/flatbuffers/src/endian_scalar.rs

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-use std::mem::size_of;
+use core::mem::size_of;
 
 /// Trait for values that must be stored in little-endian byte order, but
 /// might be represented in memory as big-endian. Every type that implements

rust/flatbuffers/src/follow.rs

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-use std::marker::PhantomData;
+use core::marker::PhantomData;
 
 /// Follow is a trait that allows us to access FlatBuffers in a declarative,
 /// type safe, and fast way. They compile down to almost no code (after

rust/flatbuffers/src/lib.rs

@@ -28,6 +28,14 @@
 //! At this time, to generate Rust code, you will need the latest `master` version of `flatc`, available from here: https://github.com/google/flatbuffers
 //! (On OSX, you can install FlatBuffers from `HEAD` with the Homebrew package manager.)
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(feature = "std")]
+extern crate core;
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
 mod builder;
 mod endian_scalar;
 mod follow;

rust/flatbuffers/src/primitives.rs

@@ -14,9 +14,9 @@
  * limitations under the License.
  */
 
-use std::marker::PhantomData;
-use std::mem::size_of;
-use std::ops::Deref;
+use core::marker::PhantomData;
+use core::mem::size_of;
+use core::ops::Deref;
 
 use endian_scalar::{emplace_scalar, read_scalar, read_scalar_at};
 use follow::Follow;

rust/flatbuffers/src/push.rs

@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
-use std::cmp::max;
-use std::mem::{align_of, size_of};
+use core::cmp::max;
+use core::mem::{align_of, size_of};
 
 use endian_scalar::emplace_scalar;
 

rust/flatbuffers/src/vector.rs

@@ -14,10 +14,10 @@
  * limitations under the License.
  */
 
-use std::marker::PhantomData;
-use std::mem::size_of;
-use std::slice::from_raw_parts;
-use std::str::from_utf8_unchecked;
+use core::marker::PhantomData;
+use core::mem::size_of;
+use core::slice::from_raw_parts;
+use core::str::from_utf8_unchecked;
 
 #[cfg(target_endian = "little")]
 use endian_scalar::EndianScalar;

rust/flatbuffers/src/vtable_writer.rs

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-use std::ptr::write_bytes;
+use core::ptr::write_bytes;
 
 use endian_scalar::{emplace_scalar, read_scalar};
 use primitives::*;