add claim_mut

tests/cfail/claim_mut.rs

@@ -0,0 +1,34 @@
+#![feature(const_fn)]
+
+extern crate cortex_m_srp;
+
+use cortex_m_srp::{C2, P2, Resource};
+
+static R1: Resource<i32, C2> = Resource::new(0);
+
+fn j1(mut prio: P2) {
+    // OK only one `&mut-` reference to the data
+    let r1: &mut i32 = R1.claim_mut(&mut prio);
+}
+
+fn j2(prio: P2) {
+    // OK two `&-` references to the same data
+    let r1: &i32 = R1.claim(&prio);
+    let another_r1: &i32 = R1.claim(&prio);
+}
+
+fn j3(mut prio: P2) {
+    // CAN'T have a `&-` reference and a `&mut-` reference to the same data
+    let r1: &i32 = R1.claim(&prio);
+    let another_r1: &mut i32 = R1.claim_mut(&mut prio);
+    //~^ error
+}
+
+fn j4(mut prio: P2) {
+    // CAN'T have two `&mut-` references to the same data
+    let r1: &mut i32 = R1.claim_mut(&mut prio);
+    let another_r1: &mut i32 = R1.claim_mut(&mut prio);
+    //~^ error
+}
+
+fn main() {}