add a "const-fn" feature

Author: japaric

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [v0.5.1] - 2018-05-13
+
+### Added
+
+- An opt-in `"const-fn"` feature that makes `Mutex.new` constructor into a `const fn`. This feature
+  requires a nightly toolchain.
+
 ## [v0.5.0] - 2018-05-11
 
 ### Added
@@ -44,6 +51,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - [breaking-change] removed several fields from `cpuid::RegisterBlock` on ARMv6-M. These registers
   are not available on that sub-architecture.
 
+- [breaking-change] The `Mutex.new` constructor is not a `const fn` by default. To make it a `const
+  fn` you have to opt into the `"const-fn"` feature, which was added in v0.5.1, and switch to a
+  nightly compiler.
+
 ### Removed
 
 - [breaking-change] The `exception` module has been removed. A replacement for `Exception::active`

Cargo.toml

@@ -7,7 +7,7 @@ keywords = ["arm", "cortex-m", "register", "peripheral"]
 license = "MIT OR Apache-2.0"
 name = "cortex-m"
 repository = "https://github.com/japaric/cortex-m"
-version = "0.5.0"
+version = "0.5.1"
 
 [build-dependencies]
 cc = "1.0.10"
@@ -19,4 +19,5 @@ volatile-register = "0.2.0"
 
 [features]
 cm7-r0p1 = []
-inline-asm = []
+const-fn = ["bare-metal/const-fn"]
+inline-asm = []

ci/script.sh

@@ -4,15 +4,15 @@ main() {
     cargo check --target $TARGET
 
     if [ $TRAVIS_RUST_VERSION = nightly ]; then
-        cargo check --target $TARGET --features inline-asm
+        cargo check --target $TARGET --features 'const-fn inline-asm'
     fi
 
     case $TARGET in
         thumbv7em-none-eabi*)
             cargo check --target $TARGET --features cm7-r0p1
 
             if [ $TRAVIS_RUST_VERSION = nightly ]; then
-                cargo check --target $TARGET --features 'cm7-r0p1 inline-asm'
+                cargo check --target $TARGET --features 'cm7-r0p1 const-fn inline-asm'
             fi
             ;;
 

src/lib.rs

@@ -30,6 +30,12 @@
 //! API docs for details.
 //!
 //! The disadvantage is that `inline-asm` requires a nightly toolchain.
+//!
+//! ## `const-fn`
+//!
+//! Enabling this feature turns the `Mutex.new` constructor into a `const fn`.
+//!
+//! This feature requires a nightly toolchain.
 
 #![cfg_attr(feature = "inline-asm", feature(asm))]
 #![deny(missing_docs)]