introduce explicit "no_std" to avoid compiler errors on targets without "std"

.github/workflows/ci.yml

@@ -12,6 +12,26 @@ jobs:
       - run: ./examples/run_examples.sh
       - run: ./examples/example_crates/run_example_crates.sh
 
+  multi-targets-no-std:
+    name: multi-targets no_std
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target:
+          - x86_64-unknown-linux-gnu
+          - x86_64-unknown-none
+          - aarch64-unknown-linux-gnu
+          - aarch64-unknown-none-softfloat
+          - riscv64gc-unknown-none-elf
+          - riscv64imac-unknown-none-elf
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: ${{ matrix.target }}
+          components: rustc, cargo
+      - run: cargo build --target ${{ matrix.target }} --no-default-features
+
   rustfmt-check:
     name: rustfmt check
     runs-on: ubuntu-latest

examples/example_crates/no_std/Cargo.toml

@@ -9,3 +9,8 @@ version = "0.1.0"
 
 [dependencies]
 enumerable = { path = "../../../", default-features = false }
+
+[profile]
+dev.panic = "abort"
+release.panic = "abort"
+

examples/example_crates/no_std/src/main.rs

@@ -1,6 +1,6 @@
 //! This example tests the `Enumerable` derive macro in a `no_std` environment.
-
-#![no_std]
+//! 
+//! This example itself is not `no_std`, but it uses the `enumerable` crate with `default-features = false`.
 
 use enumerable::Enumerable;
 

src/lib.rs

@@ -1,3 +1,4 @@
+#![cfg_attr(not(feature = "std"), no_std)]
 #![doc = include_str!("./CRATE_DOC.md")]
 
 /// `Enumerable` is a trait for types that can have their possible values enumerated.