Rust fix compilation for no_std targets #2 (#7553)

* Fix nightly no_std

* Fix nightly no_std

tests/RustTest.bat

@@ -21,3 +21,10 @@ cargo run --bin=flatbuffers_alloc_check || exit /b 1
 cargo run --bin=flexbuffers_alloc_check || exit /b 1
 cargo run --bin=monster_example || exit /b 1
 cd ..
+
+cd rust_no_std_compilation_test
+rustup install nightly
+rustup component add rust-src --toolchain nightly
+rustup target add thumbv7m-none-eabi
+cargo build || exit /b 1
+cd ..

tests/RustTest.sh

@@ -35,11 +35,18 @@ cd ./rust_serialize_test
 cargo run $TARGET_FLAG -- --quiet
 check_test_result "Rust serde tests"
 
+cd ../rust_no_std_compilation_test
+rustup install nightly
+rustup component add rust-src --toolchain nightly
+rustup target add thumbv7m-none-eabi
+cargo +nightly build
+check_test_result "Rust flatbuffers test no_std compilation"
+
 cd ../rust_usage_test
 cargo test $TARGET_FLAG -- --quiet
 check_test_result "Rust tests"
 
-cargo test $TARGET_FLAG --no-default-features --features no_std -- --quiet
+cargo test $TARGET_FLAG --no-default-features -- --quiet
 check_test_result "Rust tests (no_std)"
 
 cargo run $TARGET_FLAG --bin=flatbuffers_alloc_check

tests/rust_no_std_compilation_test/.cargo/config.toml

@@ -0,0 +1,5 @@
+[build]
+target = "thumbv7m-none-eabi"
+
+[unstable]
+build-std = ["core", "alloc"]

tests/rust_no_std_compilation_test/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "rust_test_no_std_compilation"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+flatbuffers = { path = "../../rust/flatbuffers", default-features = false }
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"

tests/rust_no_std_compilation_test/src/main.rs

@@ -0,0 +1,34 @@
+#![no_std]
+#![no_main]
+#![feature(default_alloc_error_handler)]
+
+// Include flatbuffers purely to check that it compiles in a no_std binary
+#[allow(unused_imports)]
+use flatbuffers;
+
+// The rest is just no_std boilerplate
+
+use core::alloc::{GlobalAlloc, Layout};
+
+struct NullAllocator;
+unsafe impl GlobalAlloc for NullAllocator {
+    unsafe fn alloc(&self, _lt: Layout) -> *mut u8 {
+        core::ptr::null_mut()
+    }
+    unsafe fn dealloc(&self, _ptr: *mut u8, _lt: Layout) {
+        panic!("won't deallocate: we never allocated!");
+    }
+}
+
+#[global_allocator]
+static A: NullAllocator = NullAllocator;
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[no_mangle]
+pub extern "C" fn main(_argc: i32, _argv: *const *const u8) -> i32 {
+    0
+}

tests/rust_usage_test/Cargo.toml

@@ -16,7 +16,7 @@ libc_alloc = { version = "1.0.3", optional = true }
 
 [features]
 default = ["flatbuffers/default"]
-no_std = ["flatbuffers/no_std", "libc_alloc"]
+no_std = ["libc_alloc"]
 
 [[bin]]
 name = "monster_example"