#![no_std], embedded support (#246)

.github/workflows/build.yaml

@@ -53,6 +53,49 @@ jobs:
           command: check
           args: --features serde,deprecated,panicking-api,rand
 
+  check-embedded:
+    name: Type checking (embedded)
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust: [1.34.0, 1.36.0, stable]
+
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Cache target
+        uses: actions/cache@v1
+        env:
+          cache-name: target
+        with:
+          path: ./target
+          key: ubuntu-latest-typecheck-target-${{ matrix.rust }}-thumbv7em-none-eabihf
+
+      - name: Install toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust }}
+          target: thumbv7em-none-eabihf
+          override: true
+
+      # ensure `#![no_std]` support
+      - name: Run `cargo check --no-default-features`
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --no-default-features --target thumbv7em-none-eabihf
+        if: matrix.rust != '1.34.0' # alloc is unstable in 1.34
+
+      # `#![no_std]` with serde, rand
+      - name: Run `cargo check --no-default-features --features serde,rand`
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --no-default-features --features serde,rand --target thumbv7em-none-eabihf
+        if: matrix.rust != '1.34.0' # alloc is unstable in 1.34
+
   test:
     name: Test suite
     runs-on: ${{ matrix.os }}

Cargo.toml

@@ -32,7 +32,7 @@ cfg-if = "0.1.10"
 rand = { version = "0.7", optional = true, default-features = false }
 rustversion = "1"
 serde = { version = "1", optional = true, default-features = false, features = ["derive"] }
-standback = { version = "0.2", default-features = false }
+standback = { version = "0.2.3", default-features = false }
 time-macros = { version = "0.1", path = "time-macros" }
 
 [workspace]

build.rs

@@ -14,12 +14,6 @@ fn features(features: &[(&str, &str)]) {
     }
 }
 
-fn no_std() {
-    if env::var("CARGO_FEATURE_STD").is_err() {
-        println!("cargo:rustc-cfg=no_std");
-    }
-}
-
 #[rustversion::since(1.40.0)]
 fn non_exhaustive() {
     println!("cargo:rustc-cfg=supports_non_exhaustive");
@@ -38,6 +32,5 @@ fn main() {
         ("SERDE", "serde"),
         ("__DOC", "docs"),
     ]);
-    no_std();
     non_exhaustive();
 }

src/format/format.rs

@@ -1,6 +1,6 @@
 //! The `Format` struct and its implementations.
 
-#[cfg(no_std)]
+#[cfg(not(std))]
 use crate::internal_prelude::*;
 
 /// Various well-known formats, along with the possibility for a custom format

src/format/parse_items.rs

@@ -1,7 +1,7 @@
 //! Parse formats used in the `format` and `parse` methods.
 
 use crate::format::{FormatItem, Padding, Specifier};
-#[cfg(no_std)]
+#[cfg(not(std))]
 use crate::internal_prelude::*;
 
 /// Parse the formatting string. Panics if not valid.

src/lib.rs

@@ -141,7 +141,7 @@
 //! | `0`              | Pad with zeros  | `%0d` => `05` |
 
 #![cfg_attr(docs, feature(doc_cfg))]
-#![cfg_attr(no_std, no_std)]
+#![cfg_attr(not(std), no_std)]
 #![deny(
     unsafe_code, // Used when interacting with system APIs
     anonymous_parameters,
@@ -203,7 +203,7 @@ compile_error!("The `__doc` feature requires a nightly compiler, and is for inte
 #[rustversion::before(1.34.0)]
 compile_error!("The time crate has a minimum supported rust version of 1.34.0.");
 
-#[cfg(no_std)]
+#[cfg(not(std))]
 #[rustversion::before(1.36.0)]
 compile_error!(
     "Using the time crate without the standard library enabled requires a global allocator. This \
@@ -218,7 +218,7 @@ macro_rules! format_conditional {
     };
 
     ($first_conditional:ident, $($conditional:ident),*) => {{
-        #[cfg(no_std)]
+        #[cfg(not(std))]
         let mut s = alloc::string::String::new();
         #[cfg(std)]
         let mut s = String::new();
@@ -457,7 +457,7 @@ pub mod prelude {
 mod internal_prelude {
     #![allow(unused_imports)]
 
-    #[cfg(no_std)]
+    #[cfg(not(std))]
     extern crate alloc;
 
     #[cfg(std)]
@@ -469,7 +469,7 @@ mod internal_prelude {
         PrimitiveDateTime, Time, UtcOffset,
         Weekday::{self, Friday, Monday, Saturday, Sunday, Thursday, Tuesday, Wednesday},
     };
-    #[cfg(no_std)]
+    #[cfg(not(std))]
     pub(crate) use alloc::{
         borrow::ToOwned,
         boxed::Box,

time-macros/src/lib.rs

@@ -1,3 +1,5 @@
+#![no_std]
+
 use proc_macro_hack::proc_macro_hack;
 
 #[proc_macro_hack]