Add no-allocator crate

In order to test that `bech32` can be built in a `no_std` environment
without an allocator add a crate `no-allocator` to the `embedded`
directory. Add a CI job to build the crate.

Author: tcharding

.github/workflows/rust.yml

@@ -85,3 +85,19 @@ jobs:
           RUSTFLAGS: "-C link-arg=-Tlink.x"
           CARGO_TARGET_THUMBV7M_NONE_EABI_RUNNER: "qemu-system-arm -cpu cortex-m3 -machine mps2-an385 -nographic -semihosting-config enable=on,target=native -kernel"
         run: cd embedded/with-allocator && cargo run --target thumbv7m-none-eabi
+
+  EmbeddedNoAlloc:
+    name: no_std no alloc
+    runs-on: ubuntu-latest
+    strategy:
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: rustc
+          args: -- -C link-arg=-nostartfiles

.gitignore

@@ -2,5 +2,7 @@
 *.o
 /Cargo.lock
 
+/embedded/no-allocator/Cargo.lock
+/embedded/no-allocator/.cargo
 /embedded/with-allocator/Cargo.lock
 /embedded/with-allocator/.cargo

embedded/no-allocator/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+authors = ["Tobin C. Harding <[email protected]>"]
+edition = "2018"
+readme = "README.md"
+name = "no-allocator"
+version = "0.1.0"
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"
+
+[dependencies]
+bech32 = { path = "../../", default_features = false }

embedded/no-allocator/README.md

@@ -0,0 +1,10 @@
+# no_std test crate without an allocator
+
+This crate is based on the blog post found at:
+
+ https://blog.dbrgn.ch/2019/12/24/testing-for-no-std-compatibility/
+
+Its purpose is to test that the `rust-bech32` library can be built in a `no_std` environment without
+a global allocator.
+
+Build with: `cargo rustc -- -C link-arg=-nostartfiles`.

embedded/no-allocator/src/main.rs

@@ -0,0 +1,26 @@
+//! Test `no_std` build of `bech32`.
+//!
+//! Build with: `cargo rustc -- -C link-arg=-nostartfiles`.
+//!
+
+#![no_std]
+#![no_main]
+
+use core::panic::PanicInfo;
+
+// Note: `#[global_allocator]` is NOT set.
+
+#[allow(unused_imports)]
+use bech32;
+
+/// This function is called on panic, defining this ensures build will fail if `std` is enabled
+/// because `panic` will be defined twice.
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+    loop {}
+}
+
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    loop {}
+}